VII. THE BACTERIOLOGY OF INFLUENZAL PNEUMONIA
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.)