AN INTENSIVE STUDY OF THE SPREAD OF INFLUENZA IN SMALL GROUPS OF CLOSELY
ASSOCIATED INDIVIDUALS.
We have been discussing the disease under consideration chiefly from the
viewpoint of the statistician. The statistician, possessing a wealth of
information of a general nature, and from all parts of the world, and
armed with fascinating complex mathematical instruments, is able to
dissect the information at his disposal, and to reconstruct therefrom
both facts and apparent facts of absorbing interest. To him we are
indebted for the bulk of our knowledge of the distribution and spread of
the influenza through metropolises, through countries, and through
continents.
Like the aviator flying over enemy territory he acquires a breadth of
vision and a general perspective which is to a great extent denied to
those remaining on the ground. But also like the aviator, from the very
fact of his high position he loses the ability to recognize detail. The
small subdivisions in the enemy lines are slightly blurred and he can
distinguish the front line trenches in which most of the action is
occurring no more clearly than the reserve and support trenches. An Army
depending entirely upon its aeroplane reconaissance would find itself
helpless in combating the enemy. The aeroplane is useful, yes, it could
not be dispensed with, but never an opportunity is lost for scouting
parties to explore the enemy front lines; it is these latter who bring
back information as to the local strength and distribution of the enemy,
as to what particular divisions are in action, as to the strength of the
entrenchments, the enemy distribution within the trenches, and finally
what is most important, information as to the weak points in the enemy’s
lines, places at which we may concentrate our attack with the hope of
driving the enemy from its stronghold. Occasionally a raiding party will
return with a prisoner. He will be examined thoroughly and may yield
some valuable information. All such prisoners are not dressed alike. We
recognize that some belong to one regiment and some to another. After we
have extracted what information we can from the prisoner he is
incarcerated, if we may extend our metaphor, in a test tube, and there
he remains for future reference. We do not believe that these individual
private soldiers are the cause of the war, but we do know that they are
doing their share of the killing—that they are doing most of the
killing.
It is characteristic of human enthusiasm and hopefulness that each
raiding party prays that it may bring back with it a general officer, a
field marshall, the one who is chiefly responsible for the enemy
offensive. In our own little battle with our invisible host we have long
since discovered that field marshalls here as elsewhere are difficult to
discover by raiding parties. But the raids are and should be made just
the same. They almost invariably bring back some new item of
information, and it is the experience of many wars that even though the
commanding general be never captured, repeated small or large attacks
following preliminary reconaissance, if diligently and valiantly
prosecuted under good leadership may win the war.
In studying the life and habits of the influenza virus and its army of
secondary invaders, and the results thereof in small groups composed of
individuals as the unit, instead of large groups with communities as a
unit, we will be able to discover a certain number of additional facts,
some of which may have considerable value.
In the study by the author of six selected districts in Boston a special
study was made of the occurrence and manner of spread of the influenza
in the household or family as a unit. The 10,000 individuals canvassed
were distributed through 2,117 families. Of these two thousand odd
families, 45.44 per cent. were visited with one or more cases of the
disease in the 1918–19 epidemic, and 27.25 per cent. in the winter of
1920. Of these, 14.31 per cent. had cases in both epidemics. In either
one or both of the two epidemics under consideration, 58.38 per cent. of
all families had influenza (see Table III).
TABLE III.
_Per cent. of families invaded by influenza._
═══════════════╤═════════════╤═════════════╤═════════════╤═════════════
Boston District│ 1918–19. │ 1920. │ 1918–19 and │ Total.
No. │ │ │ 1920. │
───────────────┼─────────────┼─────────────┼─────────────┼─────────────
1 │ 49.59│ 32.79│ 20.05│ 62.33
2 │ 36.04│ 17.36│ 7.25│ 46.15
3 │ 45.89│ 26.43│ 14.71│ 57.61
4 │ 48.48│ 32.20│ 14.39│ 66.29
5 │ 52.48│ 34.11│ 19.53│ 67.06
6 │ 43.16│ 24.21│ 11.23│ 56.14
All Districts │ 45.44│ 27.25│ 14.31│ 58.38
───────────────┴─────────────┴─────────────┴─────────────┴─────────────
Explanatory note: 45.44 per cent. of all families were invaded in 1918.
27.25 per cent. of all families were invaded in 1920.
14.31 per cent. of all families were invaded in both
epidemics.
58.38 per cent. of all families were invaded in one
or the other or both.
41.62 per cent. of all families remained free from
influenza throughout both epidemics.
In this discussion of family incidence, as in our work on the incidence
among individuals, the question naturally arises as to the reliability
of our information and the accuracy of our results. We have shown the
close correspondence between our own results and those of Frost, done on
a vastly larger number of individuals. The information for families was
obtained from the same sources and from the same individuals. The
thoroughness with which the inspectors did their work is indicated by
the fact that in addition to the 2,117 families on which we base our
results, only the records of 194 families have been discarded for
various reasons. In discarding the family records we also discarded the
individual records and such are, therefore, for individuals above our
total of 10,000. One hundred and fifty-four of these were for families
whose homes were in the districts surveyed, but who were not at home at
the time of the first survey. These were omitted during the second
survey, irrespective of whether individuals were at home. In this group
are also included a few in which children were at home, but were unable
to give reliable information. Fifteen of the 194 families gave
insufficient information, and 25 refused to co-operate. The small number
in this last group speaks well for the efficiency and methods of the
inspectors. All families accepted for tabulation co-operated to the best
of their ability, and we believe that the records are as accurate as
this type of work may be made.
Dr. Niven, in the work referred to by Carnwath, made an inquiry covering
1,021 houses, with a population of 4,721. Five hundred and three
households or almost exactly one-half, were invaded in either the summer
1918, or the autumn-winter 1918 epidemic. This proportion of families is
quite similar to our own, but it must be pointed out that Niven was not
studying the same two epidemics that we are discussing. Two hundred and
sixty-six of his total households, or 26.05 per cent. were invaded in
the autumn epidemic.
Previous to the present time the author has been unable to find records
of investigators having used this method of studying influenza to any
appreciable extent. Certainly there has been nothing done on the subject
previous to the last pandemic. Since then Frost has studied, as
indicated in his report, family incidence to the extent of determining
the relationship to overcrowding and to economic status, and Niven has
studied family incidence with special reference to immunity.
Thomas Sydenham, speaking of the epidemic of 1675, says that: “No one
escaped them whatever might be his age or temperament, and they ran
through whole families at once.”
According to Waldschmidt, during the epidemic of 1712, in Kiel, ten or
more persons were frequently taken ill in one house.
In 1732, Huxam tells us that, “not a house was free from it, the
beggar’s hut and the nobleman’s palace were alike subject to its attack,
scarce a person escaping either in town or country, old and young,
strong and infirm, shared the same fate.”
Metzger says that the influenza was so universal in March, 1782, that in
very many houses all of the inmates were attacked. On the other hand,
Mertens did not believe the influenza a contagion during the same
epidemic for the reason that according to his observations now only one,
and again all, of the members of a family, were stricken.
In 1833, in Königsberg, according to Hufeland, parents, children, and
servants were frequently smitten with the disease at the same time, so
that strange help had to be obtained for the family.
Parkes taught that, “Persons in overcrowded habitations have,
particularly in some epidemics, especially suffered, and several
instances are on record of a large school or a barrack for soldiers
being first attacked, and of the disease prevailing there for some days
before it began to prevail in the town around. Sometimes, on the other
hand, schools and prisons have escaped. A low, damp, ill-ventilated and
unhealthy situation appears to predispose to it, and in some instances,
in hospital patients, it has assumed a malignant character. In other
cases again, hospital patients have escaped; for example, the old people
in the Salpêtrière in 1837, when the younger attendants were attacked.”
_Effect of overcrowding._—The family or household forms a social unit in
which human intercourse is very close, and in which the opportunities
for contact infection either direct or indirect are manifold. In
addition to all of the opportunities which each individual has for
contracting the disease outside of the family every case in the family
exposes every other member many times during the day. One of the first
questions arising in a study of the disease in the family is, therefore,
whether the size of the family in and of itself exerts any predisposing
influence on the total incidence in any one family. Are large families
more likely to have a greater percentage of cases than small families?
We have endeavored to answer this question by grouping together all
families containing only one individual, all of those with two, three,
four, etc., and determining the percentage of individuals contracting
influenza in each of the groups. The standard for comparison is the
percentage of the total 10,000 who contracted the disease in either
year, or in both. 19.71 per cent. of all persons canvassed contracted
influenza in 1918–19. Reference to Table IV shows that of persons living
in families of one, 17.95 per cent. developed the disease; of those in
families of two, 18.46 per cent.; in families of three, 19.96 per cent.;
in families of four, 20.10 per cent.; and in families of from five to
seven, between 22 and 23 per cent. Families of over seven all showed
lower, but varying incidence of the disease. As is seen by the table,
they comprise only a small number of families.
TABLE IV.
_The incidence of influenza in families of different sizes._
(Influence of size of family).
═══════════╤═══════════╤═══════════╤═══════════════════════════════════
│ │ Total No. │
No. of │ │ of │
individuals│No. of such│individuals│ Number of these individuals who
in family. │ families. │included in│ developed influenza.
│ │ all such │
│ │ families. │
───────────┼───────────┼───────────┼───────────┬───────────┬───────────
„ │ „ │ „ │ 1918. │ 1920. │ Total.
───────────┼───────────┼───────────┼─────┬─────┼─────┬─────┼─────┬─────
„ │ „ │ „ │ No. │ Per │ No. │ Per │ No. │ Per
│ │ │ │cent.│ │cent.│ │cent.
───────────┼───────────┼───────────┼─────┼─────┼─────┼─────┼─────┼─────
1│ 39│ 39│ 7│17.95│ 3│ 7.69│ 10│24.42
2│ 260│ 520│ 96│18.46│ 55│10.58│ 151│29.04
3│ 359│ 1077│ 215│19.96│ 128│11.88│ 343│31.85
4│ 396│ 1584│ 319│20.10│ 169│10.67│ 488│30.81
5│ 375│ 1875│ 423│22.56│ 203│10.83│ 626│33.39
6│ 264│ 1584│ 361│22.79│ 151│ 9.53│ 512│32.32
7│ 179│ 1253│ 279│22.27│ 109│ 8.70│ 388│30.96
8│ 103│ 824│ 156│18.93│ 55│ 6.67│ 211│25.61
9│ 57│ 513│ 85│16.57│ 21│ 4.09│ 106│20.66
10│ 28│ 280│ 40│14.14│ 26│ 9.29│ 66│23.57
11│ 15│ 165│ 10│ 6.06│ 7│ 4.24│ 17│10.30
12│ 4│ 48│ 0│ 0.0│ 5│10.42│ 5│10.42
13│ 2│ 26│ 5│19.23│ 3│11.54│ 8│30.77
14│ 1│ 14│ 0│ 0.0│ 0│ 0.0│ 0│ 0.0
───────────┴───────────┴───────────┴─────┴─────┴─────┴─────┴─────┴─────
In 1920, 9.55 per cent. of the entire canvassed population contracted
the disease. The table shows that 7.69 per cent. of all individuals in
families of one contracted influenza, and between 10 and 12 per cent. in
families of from two to five individuals. Above the family of five the
incidence rates again are lower and varying within wide limits. The last
column shows the percentage of individuals by size of family contracting
the disease in either or both epidemics.
The average size of all families was 4.7 individuals.
If we consider only those family groups having over 1,000 individuals as
being sufficiently large to be representative, we may conclude that
families of from three to seven individuals show no progressive increase
in influenza incidence with increase in size of the family. But all the
available evidence indicates that other things being equal, the age
incidence is a very important factor. Its influence will be felt in the
subject under consideration, and it will modify the results. Thus,
families of one or two are almost invariably adults; families of three
are very frequently made up of two adults and a child or infant, while
families of from five to seven will be more likely to have a high
proportion of young adults—the age period more seriously affected.
The next question arising is whether those families, large or small,
which are living in crowded circumstances, are more likely to develop
the disease. Arbitrary standards must be chosen as indices of crowding.
We have chosen two in order that they may check each other. The first is
based upon the number of individuals sleeping in a bedroom. Families are
classified as follows: Maximum sleeping in a single bedroom, 1; maximum
sleeping in a single bedroom, 2; maximum per bedroom, 3, 4, etc.
The second standard of crowding is based upon the ratio of the number of
individuals in the family and the number of rooms occupied. One person
living in one room is not crowded; two in two rooms, three in three
rooms, four in four rooms, eight in eight rooms, twelve in twelve rooms,
are not crowded. Two people living in one room four in two rooms, six in
three rooms, twelve in six rooms, are decidedly more crowded. On the
contrary, one individual in two rooms, two in four, three in six, four
in eight, five in ten, etc. have an unusual amount of room.
The ratios ^P⁄_{R} are then throughout, ¹⁄₁, ²⁄₁, ½. These are used as
dividing lines. All families with ratios higher than ²⁄₁ are classed as
very crowded. Families with ratios above ¹⁄₁ up to and including ²⁄₁ are
classed as crowded. Families with ratios above ½ up to and including ¹⁄₁
are classed as roomy, and those with ratio of ½ or lower are classified
as very roomy.
Classifying all families in all six districts according to these last
four degrees of crowding, we find, as is shown by Table V, that there is
a progressive increase in the proportion of families with one or more
cases of the disease, with increase in the extent of crowding.
According to the standard first described we find as is shown in Table
VI that families with three, four and five individuals sleeping in a
single room show a progressive increase of incidence over those families
with but one or two per bedroom. This again is shown best in the total
for all families, but is borne out in a study of each district. These
statistics are however of little value for the study of the effect of
overcrowding, because crowded families are usually large families. With
an influenza incidence of 20 per cent. we would theoretically expect
every family of five or larger to have one or more cases. This would
amount to 100 per cent. infected families and such a state would not
only influence, but dominate the statistics regarding overcrowding.
TABLE V.
_Effect of crowding on development of influenza in families._
(A higher proportion of crowded households than roomy are invaded).
(Standard used: ratio of number individuals to number rooms).
══════════════╤══════════╤═════════════════════════════════════════════
Living │ No. of │ Proportion of these families visited by
conditions. │ such │ influenza.
│families. │
──────────────┼──────────┼──────────┬──────────┬────────────┬──────────
│ │ In │ │ In both │ Total
„ │ „ │ 1918–19. │ In 1920. │ epidemics │ families
│ │ │ │(Recurrent).│ invaded.
──────────────┼──────────┼────┬─────┼────┬─────┼─────┬──────┼────┬─────
„ │ „ │No. │ Per │No. │ Per │ No. │ Per │No. │ Per
│ │ │cent.│ │cent.│ │cent. │ │cent.
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District I. │ │ │ │ │ │ │ │ │
V. Cr. │ 53│ 30│56.61│ 15│28.31│ 12│ 22.64│ 31│58.49
Cr. │ 195│ 107│54.87│ 59│30.26│ 43│ 22.05│ 123│63.08
R. │ 79│ 36│45.57│ 24│30.38│ 18│ 22.78│ 42│53.16
V. R. │ 16│ 7│43.75│ 1│ 6.6│ 0│ 0.0│ 8│50.00
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District II. │ │ │ │ │ │ │ │ │
V. Cr. │ 4│ 1│25.00│ 1│25.00│ 1│ 25.00│ 1│25.00
Cr. │ 137│ 70│51.09│ 31│22.63│ 2│ 8.76│ 89│64.96
R. │ 208│ 70│33.65│ 39│18.75│ 7│ 8.17│ 92│44.23
V. R. │ 103│ 20│19.42│ 7│ 6.80│ 2│ 1.94│ 25│24.27
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District III. │ │ │ │ │ │ │ │ │
V. Cr. │ 13│ 9│69.23│ 2│15.38│ 1│ 7.69│ 10│76.92
Cr. │ 213│ 99│46.48│ 65│30.52│ 40│ 18.78│ 124│58.22
R. │ 143│ 62│43.36│ 35│24.48│ 15│ 10.49│ 82│57.34
V. R. │ 21│ 8│27.59│ 2│ 6.89│ 2│ 6.89│ 8│38.09
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District IV. │ │ │ │ │ │ │ │ │
V. Cr. │ 0│ 0│ │ 0│ │ 0│ │ 0│
Cr. │ 27│ 18│66.67│ 8│29.63│ 5│ 18.52│ 21│77.77
R. │ 137│ 72│52.55│ 50│36.49│ 21│ 15.33│ 101│73.72
V. R. │ 95│ 38│40.00│ 27│28.42│ 12│ 12.63│ 53│55.79
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District V. │ │ │ │ │ │ │ │ │
V. Cr. │ 6│ 2│33.33│ 4│66.67│ 2│ 33.33│ 4│66.67
Cr. │ 110│ 67│60.91│ 37│33.64│ 25│ 22.73│ 79│71.82
R. │ 209│ 104│49.76│ 70│33.49│ 38│ 18.18│ 146│69.86
V. R. │ 14│ 3│21.42│ 3│21.42│ 0│ │ 6│42.84
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District VI. │ │ │ │ │ │ │ │ │
V. Cr. │ 0│ 0│ │ 0│ │ 0│ │ 0│
Cr. │ 2│ 1│50.00│ 0│ 0.0│ 0│ 0.0│ 1│50.00
R. │ 92│ 57│61.96│ 23│25.00│ 14│ 15.22│ 66│71.74
V. R. │ 189│ 65│34.39│ 46│24.34│ 19│ 10.05│ 92│48.68
──────────────┴──────────┴────┴─────┴────┴─────┴─────┴──────┴────┴─────
═══════════╤══════════╤═════╤═════╤═════╤═════╤═════╤═════╤══════╤═════
Living │ No. of │ No. │ Per │ No. │ Per │ No. │ Per │ │ Per
conditions.│families. │1918.│cent.│1920.│cent.│both.│cent.│Total.│cent.
│ │ │1918.│ │1920.│ │both.│ │
───────────┼──────────┼─────┼─────┼─────┼─────┼─────┼─────┼──────┼─────
Very │ 80│ 43│53.75│ 25│31.25│ 18│22.50│ 50│62.50
crowded │ │ │ │ │ │ │ │ │
Crowded │ 693│ 372│53.68│ 201│29.00│ 126│18.18│ 447│64.50
Roomy │ 865│ 394│45.55│ 244│28.21│ 125│14.45│ 513│59.31
Very Roomy │ 443│ 143│32.28│ 87│19.64│ 36│ 8.13│ 194│43.79
───────────┼──────────┼─────┼─────┼─────┼─────┼─────┼─────┼──────┼─────
All │ Total │1918 │ Per │1920 │ Per │Both │ Per │Total │ Per
│ │ │cent.│ │cent.│ │cent.│ │cent.
───────────┼──────────┼─────┼─────┼─────┼─────┼─────┼─────┼──────┼─────
│ 2081│ 952│45.75│ 557│26.77│ 305│14.66│ 1204│57.86
───────────┴──────────┴─────┴─────┴─────┴─────┴─────┴─────┴──────┴─────
TABLE VI.
_Effect of crowding._
(Standard used: maximum number sleeping in one bed room.)
══════════════╤══════════╤═════════════════════════════════════════════
Maximum No. │ No. of │ Proportion of these families with cases of
sleeping per │ such │ influenza.
room. │families. │
──────────────┼──────────┼──────────┬──────────┬────────────┬──────────
│ │ In │ │ In both │ Total
„ │ „ │ 1918–19. │ In 1920. │ epidemics. │ families
│ │ │ │ │ invaded.
──────────────┼──────────┼────┬─────┼────┬─────┼─────┬──────┼────┬─────
„ │ „ │No. │ Per │No. │ Per │ No. │ Per │No. │ Per
│ │ │cent.│ │cent.│ │cent. │ │cent.
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District I. │ │ │ │ │ │ │ │ │
1 │ 16│ 6│37.50│ 4│25.00│ 3│ 18.75│ 7│93.75
2 │ 93│ 52│55.91│ 31│33.33│ 20│ 21.51│ 63│67.74
3 │ 145│ 65│44.83│ 47│32.41│ 27│ 18.62│ 85│58.62
4 │ 79│ 43│54.43│ 25│31.65│ 17│ 21.52│ 51│64.56
5 │ 24│ 11│45.83│ 11│45.83│ 6│ 25.00│ 16│66.67
6 │ 10│ 3│30.00│ 3│30.00│ 1│ 10.00│ 5│50.00
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District II. │ │ │ │ │ │ │ │ │
1 │ 90│ 15│16.67│ 7│ 7.77│ 2│ 2.22│ 20│22.22
2 │ 211│ 68│32.23│ 36│17.06│ 14│ 6.64│ 90│42.65
3 │ 115│ 59│51.30│ 23│20.00│ 10│ 8.69│ 72│66.61
4 │ 33│ 20│60.60│ 11│33.33│ 6│ 18.18│ 25│75.76
5 │ 3│ 1│33.33│ 2│66.67│ 1│ 33.33│ 2│66.67
6 │ 0│ 0│ │ 0│ │ 0│ │ 0│
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District III. │ │ │ │ │ │ │ │ │
1 │ 26│ 10│38.46│ 3│11.54│ 2│ 7.69│ 11│42.31
2 │ 179│ 73│40.78│ 47│26.26│ 23│ 12.85│ 97│54.19
3 │ 145│ 72│49.66│ 37│25.52│ 23│ 15.86│ 86│59.31
4 │ 39│ 20│51.28│ 15│38.46│ 8│ 20.51│ 27│69.23
5 │ 8│ 5│62.50│ 2│25.00│ 1│ 12.50│ 6│75.00
6 │ 0│ 0│ │ 0│ │ 0│ │ 0│
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District IV. │ │ │ │ │ │ │ │ │
1 │ 53│ 15│28.30│ 15│28.30│ 6│ 11.32│ 24│45.28
2 │ 165│ 80│48.48│ 56│33.94│ 22│ 13.33│ 114│69.09
3 │ 42│ 29│69.05│ 15│35.71│ 10│ 23.81│ 34│80.95
4 │ 5│ 4│80.00│ 0│ 0.0│ 0│ 0.0│ 4│80.00
5 │ 0│ 0│ │ 0│ 0.0│ 0│ │ 0│
6 │ 0│ 0│ │ 0│ │ 0│ │ 0│
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District V. │ │ │ │ │ │ │ │ │
1 │ 23│ 8│34.77│ 6│26.08│ 1│ 4.35│ 13│56.52
2 │ 156│ 70│44.37│ 48│30.77│ 24│ 15.38│ 94│60.26
3 │ 130│ 81│62.31│ 44│33.84│ 27│ 20.77│ 98│75.38
4 │ 27│ 18│66.66│ 14│51.85│ 12│ 44.44│ 20│74.07
5 │ 6│ 3│50.00│ 4│66.67│ 3│ 50.00│ 4│66.67
6 │ 1│ 0│ 0.00│ 0│ 0.00│ 0│ 0.00│ 0│ 0.00
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
District VI. │ │ │ │ │ │ │ │ │
1 │ 120│ 42│35.00│ 24│20.00│ 10│ 8.33│ 56│46.67
2 │ 146│ 77│52.74│ 34│23.29│ 22│ 15.07│ 89│60.96
3 │ 10│ 5│50.00│ 5│50.00│ 1│ 10.00│ 6│60.00
4 │ 0│ 0│ │ 0│ │ 0│ │ 0│
5 │ 0│ 0│ │ 0│ │ 0│ │ 0│
6 │ 0│ 0│ │ 0│ │ 0│ │ 0│
──────────────┼──────────┼────┼─────┼────┼─────┼─────┼──────┼────┼─────
Total │ │ │ │ │ │ │ │ │
1 │ 328│ 96│29.27│ 59│17.99│ 24│ 7.32│ 131│39.94
2 │ 450│ 420│44.21│ 252│26.53│ 125│ 13.16│ 547│57.57
3 │ 587│ 311│52.98│ 171│29.13│ 98│ 16.69│ 381│64.91
4 │ 183│ 105│57.38│ 65│35.52│ 43│ 23.50│ 127│69.39
5 │ 41│ 20│48.78│ 19│46.34│ 11│ 26.83│ 28│68.29
6 │ 11│ 3│27.27│ 3│27.27│ 1│ 9.09│ 5│45.45
──────────────┴──────────┴────┴─────┴────┴─────┴─────┴──────┴────┴─────
An objection will be raised, and justly so, that we have up to this
point been studying influenza in families irrespective of how many cases
there are in each family. Until now the family with one case was
classified exactly the same as the family with eight cases. In the
following classification we have taken first all families with a maximum
of one sleeping in one room, and sub-divided these into families with no
influenza, those with one case, two cases, etc. We have likewise
classified families with maxima from two to six per bedroom. For the
sake of brevity we will consider only the last column of Table VII,
influenza incidence among the individuals of the various classes of
families for both epidemics. Study of the table will show a
correspondence in the other columns. Solitary cases were more numerous
in families with but one or two per bedroom (27 per cent.) and less
frequent in families with three, four and five per bedroom, (23 per
cent., 18 per cent., and 20 per cent., respectively). The families of
six per bedroom form such a small group that here again they should not
be considered. Multiple cases become progressively more numerous as the
number of individuals per bedroom increases (14 per cent. in families of
one per bedroom, 29 per cent. in two per bedroom, 41 per cent. in three,
51 to 52 per cent. in four, and 45 per cent. in five). Fifty-eight per
cent. of families with a maximum of one per bedroom, 43 per cent. with
two per bedroom, 35 per cent. with three, 31 per cent. with four and 35
per cent. with five had no influenza at all.
But here again, the fact that crowded families are usually large
families interferes with drawing any conclusions. A family with four per
bed room would generally be larger than one with two per bed room.
Frost observed that, considering the ratio of incidence in total white
populations irrespective of housing as 100, and after adjusting all
groups to a uniform sex and age distribution, the ratio where there were
more than 1.5 rooms per person was 77, from 1 to 1.5 rooms per person
the ratio was 94, and for individuals averaging less than one room per
person it was 117. _The attack rate showed a consistent increase as the
number of rooms per person decreased._
Woolley observed, “Housing, if one includes in the term overcrowding,
has surely been an important factor in spreading the epidemic. Whether
it has had any appreciable effect upon the incidence of complications is
a question. The epidemic has certainly gone faster and was over sooner
because of the crowding; the hospital was filled sooner than it should
have been as a result of the rapidity of spread of the disease, and
overcrowding of the hospital occurred when with a less rapid spread it
would not have occurred; but whether the number of fatalities or the
number of pneumonias was greater than they should have been with less
crowded conditions may be doubted.”
TABLE VII.
_Relationship between crowding and number of cases in the family._
(Influenza appeared more frequently in crowded households and such
families more frequently had multiple cases.)
══════════════════════════════════════════════════════════════════════
Families with maximum per bed room of one.
(58.23 per cent. of these had no influenza.)
──────────┬──────────┬─────────┬─────────┬──────────┬─────────┬───────
Cases │Total such│ Invaded │ Invaded │Invaded in│ Total │Two or
developing│families. │ in │in 1920. │ both │families │ more
in family.│ │1918–19. │ │epidemics.│invaded. │cases.
──────────┼──────────┼───┬─────┼───┬─────┼────┬─────┼───┬─────┼───────
„ │ „ │No.│ Per │No.│ Per │No. │ Per │No.│ Per │ Per
│ │ │cent.│ │cent.│ │cent.│ │cent.│ cent.
──────────┼──────────┼───┼─────┼───┼─────┼────┼─────┼───┼─────┼───────
1│ 85│ 55│17.68│ 37│11.89│ 7│ 2.25│311│27.33│
2│ 32│ 26│ 8.36│ 16│ 5.14│ 10│ 3.22│ │10.28│} 14.44
3│ 9│ 8│ 2.57│ 2│ 0.64│ 1│ 0.32│ │ 2.88│ „
4│ 4│ 3│ 0.96│ 4│ 1.28│ 3│ 0.96│ │ 1.28│ „
5│ 0│ 0│ │ │ │ │ │ │ │
6│ 0│ │ │ │ │ │ │ │ │
7│ 0│ │ │ │ │ │ │ │ │
8│ 0│ │ │ │ │ │ │ │ │
──────────┴──────────┴───┴─────┴───┴─────┴────┴─────┴───┴─────┴───────
2 per bed room.
(43.35 per cent. of these had no influenza.)
──────────┬──────────┬───┬─────┬───┬─────┬────┬─────┬───┬─────┬───────
1│ 254│169│18.27│112│12.11│ 27│ 2.92│925│27.46│
2│ 135│112│12.11│ 64│ 6.92│ 41│ 4.43│ │14.59│} 29.17
3│ 79│ 65│ 7.03│ 38│ 4.11│ 24│ 2.59│ │ 8.54│ „
4│ 40│ 35│ 3.78│ 16│ 1.73│ 11│ 1.18│ │ 4.32│ „
5│ 11│ 9│ 0.97│ 8│ 0.81│ 6│ 0.64│ │ 1.18│ „
6│ 3│ 3│ 0.32│ 0│ 0.0│ 0│ 0.0│ │ 0.32│ „
7│ 2│ 2│ 0.22│ 1│ 0.11│ 1│ 0.11│ │ 0.22│ „
8│ 0│ 0│ │ │ │ │ │ │ │
──────────┴──────────┴───┴─────┴───┴─────┴────┴─────┴───┴─────┴───────
3 per bed room.
(35.34 per cent. of these had no influenza.)
──────────┬──────────┬───┬─────┬───┬─────┬────┬─────┬───┬─────┬───────
1│ 136│104│17.84│ 50│ 8.58│ 18│ 3.08│583│23.33│
2│ 103│ 77│13.21│ 55│ 9.43│ 29│ 4.97│ │17.67│} 41.33
3│ 59│ 51│ 8.75│ 29│ 4.97│ 21│ 3.60│ │10.12│ „
4│ 43│ 40│ 6.86│ 16│ 2.76│ 13│ 2.23│ │ 7.37│ „
5│ 22│ 22│ 3.77│ 9│ 1.54│ 9│ 1.54│ │ 3.77│ „
6│ 12│ 12│ 2.06│ 5│ 0.86│ 5│ 0.86│ │ 2.06│ „
7│ 2│ 2│ 0.34│ 0│ │ 0│ │ │ 0.34│ „
8│ 0│ │ │ │ │ │ │ │ │
──────────┴──────────┴───┴─────┴───┴─────┴────┴─────┴───┴─────┴───────
4 per bed room.
(30.79 per cent. of these had no influenza.)
──────────┬──────────┬───┬─────┬───┬─────┬────┬─────┬───┬─────┬───────
1│ 31│ 24│13.64│ 10│ 5.68│ 3│ 1.70│176│17.61│
2│ 22│ 19│10.80│ 13│ 7.39│ 10│ 5.68│ │12.50│} 51.60
3│ 37│ 32│18.18│ 25│14.20│ 20│11.36│ │20.92│ „
4│ 14│ 11│ 6.25│ 6│ 3.41│ 3│ 1.70│ │ 9.09│ „
5│ 9│ 9│ 5.12│ 4│ 2.27│ 4│ 2.27│ │ 5.12│ „
6│ 4│ 3│ 1.70│ 2│ 1.19│ 1│ 0.59│ │ 2.27│ „
7│ 3│ 3│ 1.70│ 0│ │ 0│ │ │ 1.70│ „
8│ 0│ │ │ │ │ │ │ │ │
──────────┴──────────┴───┴─────┴───┴─────┴────┴─────┴───┴─────┴───────
5 per bed room.
(35 per cent. had none.)
──────────┬──────────┬───┬─────┬───┬─────┬────┬─────┬───┬─────┬───────
1│ 8│ 6│15.00│ 4│10.00│ 2│ 5.00│ 40│20.00│
2│ 6│ 5│12.50│ 4│10.00│ 3│ 7.25│ │15.00│} 45.00
3│ 3│ 2│ 5.00│ 2│ 5.00│ 1│ 2.50│ │ 7.50│ „
4│ 2│ 1│ 2.50│ 2│ 5.00│ 1│ 2.50│ │ 5.00│ „
5│ 4│ 2│ 5.00│ 3│ 7.50│ 1│ 2.50│ │10.00│ „
6│ 2│ 2│ 5.00│ 2│ 5.00│ 2│ 5.00│ │ 5.00│ „
7│ 0│ │ │ │ │ │ │ │ │ „
8│ 1│ 0│ 0.0│ 1│ 2.50│ 0│ 0.0│ │ 2.50│ „
──────────┴──────────┴───┴─────┴───┴─────┴────┴─────┴───┴─────┴───────
6 per bed room.
(50 per cent. had none.)
──────────┬──────────┬───┬─────┬───┬─────┬────┬─────┬───┬─────┬───────
1│ 2│ 1│10.00│ 1│10.00│ 0│ 0.0│ 10│20.00│
2│ 1│ 1│10.00│ 1│10.00│ 1│10.00│ │10.00│} 30.00
3│ 2│ 1│10.00│ 1│10.00│ 0│ 0.0│ │20.00│ „
4│ 0│ │ │ │ │ │ │ │ │
5│ 0│ │ │ │ │ │ │ │ │
6│ 0│ │ │ │ │ │ │ │ │
7│ 0│ │ │ │ │ │ │ │ │
8│ 0│ │ │ │ │ │ │ │ │
──────────┴──────────┴───┴─────┴───┴─────┴────┴─────┴───┴─────┴───────
The housing methods in the cantonments and even in the tent camps
resulted in a degree of congestion and close physical contact among
individuals that was attained in no civil communities with the possible
exception of some institutions. In cantonments the number of men in
individual rooms ranged from 30 to 100 and even under the best
circumstances there was very evident close crowding. An individual in
any of these large rooms contracting a contagious disease had
opportunities to spread it by contact and by droplet infection not only
to one or two others, as in the case of the average family, but to a
large group of the men in the same room. A vicious circle was thus
formed which tended to propagate the disease throughout any camp with
utmost rapidity. Brewer has compared the influenza incidence rate in the
principal white organizations at Camp Humphreys with the floor space
allowed each man in the respective organizations, and concludes that,
“It is not proper or just to attribute the differences shown, alone to
the amount of floor space allowed each organization, but it certainly
points very strongly to the fact that the incidence of the disease
varied with the density of the population, although not with
mathematical regularity.” Brewer cites regiments which although housed
alike showed definite variation in the influenza incidence. This merely
shows that other factors also play a part. Thus, in one instance, the
difference in the two regiments was in length of service. Brewer also
found that among the white troops the incidence of pneumonia appears to
vary with the density of the population.
V. C. Vaughan has reported on the relationship between incidence in
tents and in barracks at Camp Custer. From this one observation it would
appear that the incidence is little changed under the two conditions.
“During September and October, 1918, a study was made on the
relationship, if any, of influenza to methods of living. Of the command,
3,633 were in tents. The morbidity per thousand in these was 129. There
were in barracks 36,055. The morbidity per thousand among those was 275.
At first glance the lower morbidity of those in tents is striking, but
going further into the matter it was found that the entire morbidity of
the Quartermaster Corps was very low. Of the Depot Brigade 2,881 were in
tents, with a morbidity of 128 per thousand, while 3,824 were in
barracks, with a morbidity of 134 per thousand.”
Howard and Love offer three reasons why during the last four months of
1918 the deaths from influenza and pneumonia in the Army in the United
States ran at a rate nearly three times as high as that among our troops
in France: First, that the troops in the United States were recent
recruits and therefore more susceptible to disease; second, that
probably many of the troops in France who had seen much longer service
had had the disease in mild form in the early spring; and, third, that
the method of housing was entirely different in France. There the men
were spread over a wide territory and whenever in rest area they were
billeted in houses rather than crowded into barracks. Furthermore, they
were living much more in the open. It was found that in commands of the
Service of Supply, where troops were housed in barracks with a large
number of men to a single room, the epidemic ran much the same course
with high mortality, as it did in the cantonments in the United States.
The percentage of infection and the fatalities from influenza and
pneumonia in France were much greater among troops of the S. O. S. than
among troops at the front.
_Domestic cleanliness._—We have studied the relationship between
influenza incidence and the cleanliness of the household by the same
method used in studying overcrowding. In Table VIII we have classified
according to cleanliness and according to the number of cases developing
in each family. We have had four subdivisions, “very clean,” “clean,”
“dirty,” and “very dirty.” There is greater opportunity for erroneous
results in this table than in the one preceding because the standards of
cleanliness are difficult to define. As a matter of fact we are guided
entirely by the inspector’s own impression of each household, as she
examined it during her visits. The following is an excerpt from the
instructions given each inspector on this subject:
“A few words on this subject may describe much. State of cleanliness
of the individual, slovenly condition, dust and dirt, foulness of air
noticed on first entering, condition of children, of kitchen sink,
etc., should be noticed, and good or bad features recorded. In the
poorer districts not a few families will be found in which the
cleanliness, considering the surroundings, is quite laudable. Of
particular importance are amount of daylight, ventilation, care of
bathroom and toilet, garbage, whether windows are kept open at night.”
On the basis of these returns we have classified the families as
indicated, but each inspector was governed to a certain extent by the
average cleanliness of her district, and it is difficult to compare the
cleanest tenement with any of the districts of well-to-do individuals.
We will therefore probably find it more profitable and more nearly
accurate to combine the groups and classify them only as “clean” and
“dirty.”
TABLE VIII.
_Relationship between cleanliness and number of cases in family._
(Clean families were invaded less frequently and had solitary cases more
often than did dirty households.)
══════════════════════════════════════════════════════════════════════════
Very clean.
(47.62 per cent. had none.)
─────────┬─────────┬────┬─────┬────┬─────┬─────┬─────┬──────┬─────────────
Cases in │ Total │’18.│ Per │’20.│ Per │Both.│ Per │Total.│ Per cent.
families.│families.│ │cent.│ │cent.│ │cent.│ │
─────────┼─────────┼────┼─────┼────┼─────┼─────┼─────┼──────┼─────┬───────
1│ 124│ 72│15.65│ 50│10.87│ 8│ 1.74│ 460│26.96│
2│ 53│ 41│ 8.91│ 27│ 5.87│ 15│ 3.25│ │11.52│} 25.42
3│ 37│ 33│ 7.17│ 13│ 2.82│ 9│ 1.95│ │ 8.04│ „
4│ 18│ 16│ 3.48│ 8│ 1.74│ 6│ 1.30│ │ 3.91│ „
5│ 4│ 3│ 0.65│ 2│ 0.43│ 1│ 0.21│ │ 0.87│ „
6│ 3│ 3│ 0.65│ 0│ 0.0│ 0│ 0.0│ │ 0.65│ „
7│ 2│ 2│ 0.43│ 1│ 0.21│ 1│ 0.21│ │ 0.43│ „
8│ 0│ 0│ │ 0│ │ 0│ │ │ │
─────────┴─────────┴────┴─────┴────┴─────┴─────┴─────┴──────┴─────┴───────
Clean.
(41.52 per cent. had none.)
─────────┬─────────┬────┬─────┬────┬─────┬─────┬─────┬──────┬─────────────
Cases. │Families.│’18.│ Per │’20.│ Per │Both.│ Per │Total.│ Per cent.
│ │ │cent.│ │cent.│ │cent.│ │
─────────┼─────────┼────┼─────┼────┼─────┼─────┼─────┼──────┼─────┬───────
1│ 301│ 212│18.45│ 120│10.44│ 31│ 2.70│ 1149│26.19│
2│ 177│ 143│12.45│ 91│ 7.92│ 57│ 4.96│ │15.40│} 32.29
3│ 101│ 83│ 7.22│ 52│ 4.53│ 34│ 2.96│ │ 8.79│ „
4│ 52│ 47│ 4.09│ 20│ 1.74│ 15│ 1.26│ │ 4.53│ „
5│ 30│ 29│ 2.52│ 17│ 1.48│ 16│ 1.22│ │ 2.61│ „
6│ 8│ 7│ 0.61│ 3│ 0.26│ 2│ 0.17│ │ 0.70│ „
7│ 3│ 3│ 0.26│ 0│ 0.0│ 0│ 0.0│ │ 0.26│ „
8│ 0│ 0│ │ 0│ │ 0│ │ │ │
─────────┴─────────┴────┴─────┴────┴─────┴─────┴─────┴──────┴─────┴───────
Dirty.
(36.89 per cent. had none.)
─────────┬─────────┬────┬─────┬────┬─────┬─────┬─────┬──────┬─────────────
Cases in │ Total │’18.│ Per │’20.│ Per │Both.│ Per │Total.│ Per cent.
families.│families.│ │cent.│ │cent.│ │cent.│ │
─────────┼─────────┼────┼─────┼────┼─────┼─────┼─────┼──────┼─────┬───────
1│ 79│ 59│17.40│ 36│10.62│ 16│ 4.72│ 339│23.30│
2│ 58│ 48│14.16│ 29│ 8.55│ 19│ 5.61│ │17.11│} 39.81
3│ 37│ 31│ 9.14│ 22│ 6.49│ 17│ 5.01│ │10.91│ „
4│ 26│ 22│ 6.49│ 12│ 3.54│ 8│ 2.36│ │ 7.67│ „
5│ 6│ 5│ 1.79│ 4│ 1.18│ 3│ 0.94│ │ 1.77│ „
6│ 7│ 7│ 2.06│ 4│ 1.18│ 4│ 1.18│ │ 2.06│ „
7│ 0│ 0│ │ 0│ │ 0│ │ │ │ „
8│ 1│ 0│ 0.0│ 1│ 0.29│ 0│ 0.0│ │ 0.29│ „
─────────┴─────────┴────┴─────┴────┴─────┴─────┴─────┴──────┴─────┴───────
Very dirty.
(39.26 per cent. had none.)
─────────┬─────────┬────┬─────┬────┬─────┬─────┬─────┬──────┬─────┬───────
1│ 22│ 16│14.95│ 8│ 7.47│ 2│ 1.85│ 107│20.56│
2│ 11│ 8│ 7.47│ 6│ 5.10│ 3│ 2.80│ │10.28│} 40.18
3│ 14│ 12│11.21│ 10│ 9.35│ 7│ 6.54│ │13.08│ „
4│ 7│ 5│ 4.67│ 4│ 3.73│ 2│ 1.85│ │ 6.54│ „
5│ 6│ 6│ 5.10│ 1│ 0.93│ 0│ 0.0│ │ 5.61│ „
6│ 3│ 3│ 2.80│ 2│ 1.85│ 2│ 1.85│ │ 2.80│ „
7│ 2│ 2│ 1.85│ 0│ 0.0│ 0│ 0.0│ │ 1.87│ „
8│ 0│ 0│ │ 0│ │ 0│ │ │ │
─────────┴─────────┴────┴─────┴────┴─────┴─────┴─────┴──────┴─────┴───────
But even without combining in this way, the table shows us that for both
years 27 per cent. of the very clean families, 26 per cent. of the
clean, 23 per cent. of the dirty and 21 per cent. of the very dirty, had
but one case, while 25 per cent. of the very clean, 32 per cent. of the
clean, 40 per cent. of the dirty, and 40 per cent. of the very dirty,
had multiple cases.
The cleaner the family the less is the likelihood of multiple cases.
It is rather difficult to find concrete examples of the influence of
domestic habits and environment in the 1918 pandemic. The remarkably
high incidence among the natives of India and among the American Indians
might by some be attributed to unfavorable environment. Lynch and
Cumming obtained records from a large number of institutions and from
business concerns having their own records, and discovered that the
influenza incidence was higher in those institutions where dish washing
was done manually than in those in which mechanical washing was
performed. They appear to conclude that the difference in the two
methods of washing dishes was the cause for the greater incidence in
influenza, thus bearing out their theory of the propagation of influenza
chiefly through eating utensils. On the contrary it is possible that the
presence of the mechanical washer is an indication of advanced methods,
greater care in the kitchen, and better hygiene probably not only in the
kitchen and dining room, but throughout the institution.
_Economic status._—Although in our survey information has been obtained
regarding the economic status of the various families we would not
stress this phase of our subject. Obviously the amount of money an
individual has in his bank will not directly influence the amount of
influenza he will have in his home. As nearly an accurate classification
by wealth is by the separation into the districts, Districts I and III
being very poor, District II poor, Districts IV and V moderate, and VI
well-to-do. From Chart XXVI we see no definite relationship between
influenza incidence and economic status.
Dr. Niven has had similar experiences. He remarks that the disease does
not appear to have affected especially any class or section of the
community. Rich and poor suffered alike. Inquiry in some towns shows
that the epidemic not infrequently started in the well-to-do districts
and only later involved the poorer and less prosperous areas.
We cannot state with any degree of accuracy in what section of Boston
the 1920 recurrence first began. The sections studied are for relatively
small portions of the city, and it is possible or probable that the
original increase was in some area outside of our districts. In the
districts studied the earliest increase in reported cases was from the
section of the city known as Dorchester (Districts IV and V), where
there was some increase in December, 1919. The latest definite increase
was in the Irish district of South Boston. Geographically these two
areas are quite near. The relative insusceptibility of the Irish
population is probably a much more important factor in the difference.
Frost found after classifying the white population canvassed in Little
Rock and San Antonio according to economic status, and adjusting the
incidence rate in each group to a uniform sex and age distribution, that
the ratios of incidence in each economic group to incidence in total
white population did show an increase with increasing poverty.
“Notwithstanding that the classification according to economic status is
a very loose one, based solely on the judgment of inspectors with widely
different standards, a considerably higher incidence is shown in the
lower as compared to the higher economic group.”
Parsons, in 1891, discussed the influence of poverty, but believed that
it is the concomitants of poverty which were the cause of the higher
incidence among the poor.
“Sanitary conditions do not seem to have had any influence in
determining the occurrence of influenza, and what share they have had in
determining its extent or fatality cannot yet be decided. On the
occasion of the last great epidemic, Dr. Peacock concluded, ‘The more
common predisponents to disease, _e.g._, defective drainage, want of
cleanliness, overcrowding, impure air, deficient clothing, innutritious
or too scanty food, powerfully conduce to the prevalence and fatality of
influenza.’ And Dr. Farr showed that in the last six weeks of 1847,
while in the least unhealthy districts of London the annual rate of
mortality was raised from a mean rate of twenty per 1,000 to
thirty-eight, in the unhealthiest districts it was raised from a mean
rate of twenty-seven to sixty-one.
“That overcrowding and impure air must have a powerful influence in
aiding the development of the epidemic follows from what we have seen of
its greater prevalence among persons associated together in a confined
space; and though rich and poor have alike been sufferers from the
epidemic, and even royal personages have been fatally attacked by it, it
cannot be doubted that poverty must have in many cases conduced to a
fatal issue in persons, who, if placed under more favorable
circumstances, might have recovered, seeing that it often involves not
only inferior conditions of lodgment, but also want of appropriate food,
of sufficient warmth and clothing, and of ability to take the needed
rest.”
_Distribution of the disease through the household._—During the autumn
and winter epidemic of 1918 there was considerable discussion, and
particularly were there popular newspaper reports of entire families
being taken ill with influenza, sometimes all on the same day. This was
less true of 1920. But few of us are personally acquainted with such
instances and at best they must have been relatively rare.
Among 1,236 families with influenza in either epidemic we found only 94
or 7.6 per cent. in which the entire family contracted the disease. No
family consisting of over seven individuals was reported as having all
the members of the family sick in either epidemic. Over two-thirds of
the families with even numbers of individuals (464 out of 605) suffered
the illness of less than half of the household. One quarter of all
families of more than one (539 out of 2,107) had but one case per
family. Over a third of all families of over two individuals (745 out of
2,006) had two or less cases per household. _As a rule there were at
least one and usually several individuals in each household who did not
contract influenza._
That as a rule the disease did not appear explosively in a family; but
that cases developed successively, is indicated by the fact that out of
577 families contracting influenza in the epidemic of 1920 the cases
were all of simultaneous development in but fifteen. In thirteen of
these, two individuals fell ill on the same day and no subsequent cases
developed. In the other two families three individuals came down on the
first day and no other cases developed. In addition there were, out of
the 577 families, fourteen in which there were two or more cases
developing on the first day of the invasion, but which were followed on
subsequent days by later cases in the same family. Again, there were
eleven families in which two or more cases occurred simultaneously at an
interval of one or more days after the development of a single prior
case.
We may say that _as a rule in the 1920 epidemic, cases of influenza
developed in families successively and not simultaneously_. In only 29,
or 5 per cent. of the families contracting the disease in 1920, did more
than one case develop on the first day of the appearance of the disease
in the family.
A certain difficulty in determining the date of onset is that we must
rely upon the patient’s statement. One individual may have been sick for
hours or days before a second member coming down with the disease called
forth recognition of the fact that they both had it.
Unfortunately we are not able to give similar statistics for the 1918–19
epidemic. Our investigation occurred so long after the epidemic that
specific dates of onset of the disease would have been entirely
unreliable. The nearest date we have attempted to obtain was the month
of the attack.
Dr. A. L. Mason states that 63 cases came under his observation in the
epidemic of 1889 as occurring in groups in families. In but six
instances were two persons attacked on the same day. The average
interval between cases in the same household was four days. Sometimes a
week or more elapsed. Whole families were never stricken at once.
Parsons in 1891 concluded from the results of questionaires sent to
physicians that in the first spread, 1889–90, there was an interval
between cases in individual households just as we have described. Among
the replies to his questionaires nine described intervals of one day and
under, six described intervals of two days, three of three days, three
of four days, and four replies described intervals of more than four
days.
Leichtenstern observed likewise: “In large families the contagious
character of influenza is evidenced by the fact that the other members
of the family become sick one after the other following the first case.
This rule of succession is most easily seen in the early or late period
of an epidemic and is less noticeable at the height, where the
opportunity for all the members of the family to acquire the influenza
outside the home is enormous. This latter fact explains why, when all
sicken at once, the disease appears to be miasmatic in origin. There are
many examples where other members of a family living with a sick
individual remained unaffected. Parsons reports such cases, and this was
so frequently the case that some British physicians state that it is the
rule that there is but one case in a family or that the cases are widely
separated in time. This was only partly true during the period of the
pandemic and was very frequent in the epidemic following it. In this
respect influenza acts like the common contagious diseases, diphtheria,
scarlet fever, measles, etc., while the difference lies in the short
incubation period and the very high contagiousness of the disease.”
That West, in England, had observed the same phenomenon is indicated by
the following quotation: “How is it, for instance, that one member of a
household may be picked out and the others escape, though they are
susceptible, as is shown by their acquiring the disease shortly after in
some other way?”
Again Leichtenstern wrote: “It is noteworthy that influenza on ships
usually did not occur explosively, but spread gradually, and on ships
usually lasted several weeks, as on the Bellerophon, from the 27th of
March to the 30th of April; on the Canada from the 11th of April to the
24th of May; on the Comus from the 10th of April to the 3d of May.
“The German Marine Report states, ‘Everywhere on the ships the disease
began not suddenly but gradually.’ The frigate Schwalbe first had a
large number of cases only on the 6th day after the beginning of the
epidemic. There are, however, some exceptions, where the disease has
begun suddenly with the greatest violence on ships as on land. Such was
true of the frigate Stag which on the 3d of April, 1833, neared the
influenza infected coast of Devonshire, and as it came under the land
wind the epidemic suddenly broke out with great violence. Within two
hours forty men took sick. Within six hours the number had increased to
sixty. Within twenty-four hours 160 men were sick. As Parkes has
remarked the evidence is insufficient that there had been no
communication with the coast. There have been other examples of sudden
outbreaks on ships, as on a Dutch frigate in the harbor of Mangkassar,
where 144 men out of 340 took sick in a few days (1856); on the Canopus
(1837) in the harbor of Plymouth, where on the 15th of February
three-fourths of the men took sick with influenza.”
Garvie, in reporting his personal experiences with influenza in 1918 in
an industrial area in England, experiences not based on statistical
study, concludes that there are two types of cases, the sporadic case
which occurs mainly among the wage-earning members of the family and has
little tendency to affect other members of the household, and second,
the type of case where a large number of individuals in the household
are affected. He called this the “household wave.” If we interpret him
aright he really means that there are either single or multiple cases,
and that the single cases are more apt to occur in the wage-earner, the
individual who is more exposed on the outside of the household. He also
believes that the household wave is more severe in character than the
so-called sporadic case, and is accompanied by a greater number of
complications.
Armstrong, in his survey in Framingham, examined influenza
convalescents. He found that of these 10 per cent. were in families in
which no other cases had developed, and 87 per cent. were in families
where one or more additional cases had occurred. In three per cent.
information was lacking.
It is important in studying the literature on this subject to
distinguish between definitely established fact and less definite
description. Thus one is still left in some doubt when one reads in a
London letter in the Journal of the American Medical Association for
1915 concerning the epidemic in London at that time that, “whenever it
has seized an individual it has usually run through the entire
household. Whole offices have succumbed.”
_The first case in the family._—Chart XXVII shows clearly that in both
epidemics in our experience the wage-earner was much more frequently the
first case in a family than was any other occupation. The individuals
whose occupations kept them at home were second. Infants, as was to be
expected, were recorded as being “first case” in the smallest number of
instances.
In 1889 the distribution was practically the same. Parsons found that
out of 125 households the first case was a bread-winner in 96; a
housekeeper in nine; a child at school in thirteen; a child not at
school in two families. In the last five families the first case was in
adults, occupation not given. This order is identical with our own.
Neither our own observations nor those of Parsons consider the relative
proportions of wage earners in the population as a whole. The results
are nevertheless suggestive.
H. F. Vaughan reached comparable results for the 1920 epidemic in
Detroit. During the first few weeks the age groups from 20 to 29 showed
a relatively much more frequent influenza incidence than did children up
to ten years. In later weeks of the epidemic there was a relative
increase in the incidence among children and decrease among young
adults. He concluded that the disease first attacks the young adult and
from this group it extends into the home.
In the Local Government Board Report for 1891, H. H. Murphy
distinguishes three groups or ways in which the disease may be brought
into the family. The examples will be found to be characteristic for any
epidemic and for any country:
_Group A._—Cases of single exposure.
“Household 1.—Mr. Q. goes to London daily. Was ill with influenza on
December 25th. No other case in this house till January 15th.
“Household 2.—Mrs. A. called on Mr. Q. on December 31st, and had a few
minutes’ conversation with him. She was taken ill on January 3d. There
was a Christmas family gathering at this house, and this is how the
other members were affected: Mr. B., January 6th; Miss C., Mrs. D., and
Master D., January 8th; Mr. J., January 10th; Mr. H., January 11th.
CHART XXVII.
[Illustration: Occupational distribution of first cases in each
household]
“Household 3.—Miss M. went to a party January 3d. She had a few minutes’
conversation with a young lady who said she was suffering from
influenza. Miss M. had a characteristic attack on the 6th of January.
“Household 4.—Mr. G. goes to London daily; taken ill January 5th. Mrs.
N. visited him for a short time on January 5th, and was taken ill
January 10th.”
_Group B._—Where disease was brought from a distance into a previously
healthy household.
“Household 8.—Mrs. R. G., living in the north of London, came here on a
visit December 17th. On the 19th she was taken ill with influenza, the
first case that I knew of in this neighborhood. Mr. C. G., on the 23d,
servant on the 26th, Mrs. G. 31st, and Mr. G. January 9th.
“Household 9.—Mr. I. lives at his business place in London, taken ill
December 20th with influenza. His family reside here. Boy C. visited his
father for a few days, and came back ill on January 4th. The other
members of the family were attacked as follows: Baby, 8th; Mrs. and boy,
12th; boy, 18th, girl, 22d; girl 25th.
“Household 10.—Master K. stayed a few days with some friends in London.
They had been ill with influenza. Returning home on December 31st he was
taken ill. Four brothers and sisters ill on the 2d January, Mr. K. on
3d, child and two servants on the 5th, Mrs. K. on the 7th.”
_Group C._—Where the source of infection could not be determined or was
local.
“Household 28.—Mrs. D. (who thinks she got it shopping) was taken ill 2d
January, her daughter on the 5th, and Mr. D. on 6th.
“Household 29.—Mrs. L. (who thinks she got it shopping), aged 80, had
influenza badly in 1847; similar symptoms, but much milder, on January
6, 1890; Miss L. was attacked on the 10th, and servant on the 17th.
_Note._—A former attack did not confer immunity after forty-three years.
“Household 30.—Mrs. B. (who thinks she got it out at work) taken ill 9th
January, and her child on the 11th.”
In Murphy’s complete list, one of the most frequent remarks is, Mr.
Blank goes to London daily. Or, Miss Blank, absent on a visit, was taken
ill with influenza and returned home.
Again, in 1890, Dr. Bruce Low studied the development of influenza at
East Keal, a town of 300 inhabitants. We quote in part his description:
“The following is believed to have been the commencement of the
outbreak, and for these facts I am indebted to Dr. Francis Walker,
Medical Officer of Health, Spilsby, R. S. D. Mrs. N., residing at East
Keal Hall, went to London (Forest Hill) on a visit on November 11th. She
visited Barnum’s Show on November 13th. She became ill on the night of
the 14th. Her symptoms were those of a cold, attended with sore throat.
No one else so far as she knew was ill in this way in the house before
her. She left Forest Hill on November 16th, still feeling very unwell,
and went to stay with friends at Kensington. She was too ill to return
home till November 23d, at which time she was still feeling very weak.
She heard from Forest Hill that, directly after she left one of the
inmates of the house where she had been visiting fell ill with symptoms
similar to her own. Within a few days, probably about the 27th of
November (the exact date is not fixed), of her return home, her son,
aged four, became unwell with what appeared to be an ordinary cold, but
the child had epistaxis; he soon recovered, but during the next
fortnight the four servants in the house were ill with what were said to
be ‘colds,’ one of them also had epistaxis. On January 2d another son,
aged six, was ill with ‘cold’ for a few days; he went out and had a
relapse, which compelled him to stay in the house for another week.
“On January 3d, Mrs. N. again fell ill with ‘a bad cold,’ attended with
headache, backache and epistaxis. She was in bed two days and felt
miserable and prostrate for more than a week after. On January 5th, Mr.
N., her husband, had headache, backache, and general soreness ‘all
over.’ On January 10th, the boy, aged four, who was first attacked after
his mother’s return from London, again became ill, his symptoms being
the same as before. The only other remaining member of the family who
had managed to escape an attack of ‘cold’ up to this date, was said to
have felt ill the day the boy had his second attack; but the illness of
this individual was slight, and only caused suffering for one night.
Thus between the return of the mother on November 23d and January 10th
all the inmates of this house, nine in number, had an attack of illness,
evidently of the same nature. A boy who works in Mr. N.’s yard was taken
ill with influenza about the end of November. He lives in the village.
After his illness his four brothers also were ill. Dr. Walker says that
‘about the end of November’ cases of like illness were beginning to crop
up in East Keal. Mrs. W., the wife of the village grocer and baker, who
waited on customers in the shop and never left the shop or house, was
taken ill on the afternoon of November 30th. Next morning, December 1st,
her husband and six children were all attacked in the same way with what
is now recognized to have been marked influenza. The only inmate of the
house who escaped was a youth employed to deliver bread and groceries in
a cart in the neighboring village.”
Leichtenstern relates that a physician traveling from Berlin on the 10th
of December became sick in his home town, Elgesburg, on the 8th of
December, but he made several visits and a few days later those people
seen by him fell sick, while otherwise there were no cases of influenza
in the town or its neighborhood. These cases would probably have fallen
in Group C., of Murphy’s classification.
_Intimacy of family contact._—We have been able to discover in a
representative number of families in which influenza has occurred, not
only what individuals slept in the various rooms of the household, but
also what individuals slept in the same bed with influenza cases. We
can, therefore, study for the 1920 epidemic three degrees of contact;
contact by sleeping with a case of influenza; by sleeping in the same
room but a different bed; and general contact by being in the family,
but sleeping in another room. For brevity we designate these,
“_sleeping_,” “_room_” and “_family_” _contact_. We have established
similar information for 1918, after eliminating families in which deaths
or births or other additions or losses had occurred during or subsequent
to the 1918 pandemic, in which there has been a change of address, in
which the cases are so widely separated that we have designated them
_unrelated_, and finally, those families in which the information has
been insufficient. With the remaining we have assumed that the
distribution within the household has been the same in both epidemics.
Statistics are available on 1,734 individuals who in 1918 were exposed
to a prior case in the family. Of these, 462 developed influenza and
1,272 did not. 26.6 per cent. of exposed individuals in families
contracted influenza, without respect to the degree of exposure.
═════════════════╤═════════════════╤═════════════════╤═════════════════
Intimacy of │ Number so │Number infected. │ Per cent.
contact. │ exposed. │ │ infected.
─────────────────┼─────────────────┼─────────────────┼─────────────────
“Sleeping” │ 360│ 166│ 45.2
“Room” │ 303│ 59│ 19.5
“Family” │ 1,064│ 273│ 22.3
─────────────────┴─────────────────┴─────────────────┴─────────────────
45.2 per cent. of individuals sleeping with cases of influenza in 1918
contracted the disease; 19.5 per cent. of those sleeping in the same
room, but different beds did so; 22.3 per cent. of those living in the
same family, but sleeping in other rooms contracted the disease.
_Sleeping contact is more productive of influenza than are the less
intimate forms._
Throughout this study the fact that there are multiple possible sources
of infection both outside and often within the family complicates the
picture.
The results for 1920 are similar. Here, 30.0 per cent. of all
individuals sleeping with cases of influenza contracted the disease,
17.7 per cent. of room exposures contracted it, while but 11.5 per cent.
of family exposures were attacked.
Four hundred and sixty-three or 29.1 per cent. of the total of 2,193
individuals exposed in 1920 had had the disease in the 1918 pandemic.
Did they show by reason of any immunity a lower attack rate for the same
degree of exposure than other individuals in 1920?
═══════════════════════╤═══════════════════════╤═══════════════════════
│ Per cent. of exposed │Per cent. of those who
Type of exposure in │individuals who had had│had not had a previous
1920. │ influenza in 1918–19 │ attack, and who on
│ and who contracted it │ exposure contracted
│ again, per cent. │ influenza, per cent.
───────────────────────┼───────────────────────┼───────────────────────
“Sleeping” │ 27.0│ 31.0
“Room” │ 18.3│ 17.6
“Family” │ 12.0│ 11.2
───────────────────────┴───────────────────────┴───────────────────────
_On the whole there is no evidence of protection afforded by a previous
attack._—Individuals who had had the disease before succumbed to a
second attack in the same proportion as those who had not previously had
influenza.
_Recurrent cases._—In certain families there were individuals who had
had influenza during both the 1918 and 1920 epidemics. Were these
recurrent cases the first ones to occur in the family, or did they, as a
rule, follow other cases in the same household? We have records of 236
recurrent cases in which we know the order of occurrence of the various
cases in the family. Out of this total number 57 were the initial cases
in the household. One hundred and nineteen were the only cases occurring
in the family. Therefore 176 or 74 per cent. of the total number of
recurrent cases were either the first or the only cases in the family.
Sixteen recurrent cases followed between other cases and 44 occurred as
the last of a series of two or more in the household.