Certain conclusions may be drawn from the literature on the bacteriology
of the respiratory lesions associated with influenza. All reports show
that a few organisms have been found more or less constantly in
influenza and influenzal pneumonia: the pneumococcus group, the
streptococci (hemolytic, non-hemolytic, pandemicus, etc.) and the
Pfeiffer bacillus. They may occur alone, together, or with less
frequently found organisms. Among the latter, the staphylococcus, the
Micrococcus catarrhalis, Bacillus pneumoniæ (Friedlander), diphtheroids,
and undetermined organisms, all have been reported (2, 48, 62, 67, 68,
92).
Another feature has been the variation of the predominating organism, or
organisms, in different localities, and in the same locality at
different times. For example, Wolbach (162) at Camp Devens,
Massachusetts, demonstrated the Pfeiffer bacillus at autopsy in
twenty-three out of twenty-eight cases. In fourteen, it was in pure
culture. Keegan (67) at Chelsea, Massachusetts, also found it in
eighty-two per cent of the lungs at necropsy, in thirty-one per cent of
which it was in pure culture. MacCallum (92), working at Camp Lee,
Virginia, found the pneumococcus, Type IV, the predominating organism
and rarely the Pfeiffer bacillus. “At the Johns Hopkins Hospital similar
methods revealed no influenza bacilli whatever.” At Camp Dix, New
Jersey, however, MacCallum found the Pfeiffer bacillus in every case. At
Camp Grant, Illinois, Hirsch and McKinney (60) state that the epidemic
was due to a virulent strain of pneumococcus and that the Pfeiffer
bacillus played no rôle. At the Puget Sound Navy Yard, Ely and
co-workers (37) did not find the Pfeiffer bacillus; they attributed the
epidemic to the hemolytic streptococcus. Goodpasture (48), working at
the same hospital as Keegan, reports that the bacteria found in
December, 1918, and January, 1919, were different from those found in
the early months of the epidemic, inasmuch as in the latter group the
hemolytic streptococcus was found in one hundred per cent of the cases
and the Pfeiffer bacillus in twelve per cent. The foreign literature
shows similar variations in the bacteriology.
The organisms associated with influenzal pneumonia are the so-called
“mouth organisms.” They are not only found in the mouths and upper air
passages of the influenza patients, but also in those of normal
individuals. This points to the fact that the bacteria of the mouth have
gained access to the lung, probably already injured by a primary agent,
in sufficient numbers to bring about a serious inflammatory process. In
this connection it is of interest to note the relatively high frequency
of the mouth organisms, pneumococcus, Types III and IV, in influenzal
pneumonia as compared to the less frequent mouth inhabitants, Types I
and II, which are responsible for two-thirds of the cases of true lobar
pneumonia (5, 45, 92, 121).
Only the eighty-two cases at the New Haven Hospital are included in the
following report. Routine post-mortem cultures were taken from blood,
lung, serous fluid wherever present, and exudates from the trachea and
bronchi in the later cases. Blood and serous fluids were cultured into
neutral infusion broth and plated on blood agar after twelve to
thirty-six hours’ incubation. Lung and bronchial cultures were streaked
on blood agar plates and for the last third of the series on Avery’s
oleate media. Cultures were examined on each successive day and were
discarded only after one week. Undoubtedly, we have failed to find B.
influenzæ in many of the earlier cases because of lack of familiarity
with the organism, of variations in its morphology (33), and of
unsuitable culture media. The organisms tabulated below include only
those determined by cultural methods; those found by direct smears or in
histopathological preparations are not considered. (See Table No. I.)