Bacteriologic examination showed that a very large proportion of the cases was due to infection with the different immunologic types of pneumococci or to a mixed infection with B. influenzæ and pneumococci. The types of pneumococci commonly found in normal mouths, namely, II atypical, III, and IV, comprised approximately 88 per cent of these, the highly parasitic Pneumococci Types I and II, but 12 per cent. A small number of cases were due to hemolytic streptococci or to mixed infection with B. influenzæ and S. hemolyticus. No certain evidence was obtained that pneumonia was due to B. influenzæ alone. This organism was present in varying numbers, however, in approximately 80 per cent of the sputums examined, and it seems fairly certain that it must have played at least a part in the development of the pneumonia in many of the cases in which it was found. Superimposed infections with other types of pneumococci than those primarily responsible for the development of pneumonia, with hemolytic streptococci and with Staphylococcus aureus occurred frequently in cases of pneumococcus or mixed pneumococcus and B. influenzæ pneumonia and undoubtedly contributed to a considerable extent in increasing the number of deaths.
Three clinical types of pneumococcus pneumonia following influenza occurred: lobar pneumonia, lobar pneumonia with purulent bronchitis, and bronchopneumonia. Lobar pneumonia was usually sudden in onset and ran the characteristic course of the primary disease. Lobar pneumonia with purulent bronchitis similarly ran the characteristic course of the primary disease but presented the unusual picture of lobar pneumonia with mucopurulent rather than rusty, tenacious sputum and numerous moist râles throughout the unconsolidated portions of the lungs. The cases of bronchopneumonia ran a very variable course from mild cases of a few days’ duration and meager signs of consolidation to rapidly progressive cases with signs of extensive pulmonary involvement. Purulent bronchitis was very frequently associated with bronchopneumonia.
Hemolytic streptococcus pneumonia following influenza presented the clinical picture of bronchopneumonia and was not readily distinguished on clinical grounds from pneumococcus bronchopneumonia except in those cases which developed a pleural exudate early in the disease. The advent of tertiary infection of the lower respiratory tract with hemolytic streptococci in cases of secondary pneumococcus pneumonia presented no symptoms sufficiently constant or certain to make clinical diagnosis easy. The development of empyema in pneumococcus bronchopneumonia usually meant streptococcus infection.
Pure B. influenzæ pneumonia, if such cases existed, presented no diagnostic features by which it could be distinguished from pneumococcus bronchopneumonia following influenza. It was impossible to determine on clinical and bacteriologic grounds alone what part the prevalent influenza bacilli played in the causation of the actual pneumonia.
Discussion
That wide variations in the conception of influenza have arisen during the recent pandemic, even a hasty review of the literature makes clear. In its essence this divergence of opinion seems to depend upon whether pneumonia is considered an essential part of influenza or a complication due either to the primary cause of influenza or to secondary infection. One extreme is expressed by Dunn[[30]] who says “the so-called complication is the disease,” the other by Fantus[[31]] who finds influenza a relatively mild disease with pneumonia a relatively infrequent and largely preventable complication.
A similar divergence of opinion prevails with respect to the bacteriology of influenza. There is fairly general agreement that the members of the pneumococcus and streptococcus groups and to a less extent other organisms are responsible for a large proportion of the secondary pneumonias, and but few observers hold that they possess any etiologic relationship to influenza. No such uniformity of opinion exists, however, with respect to the relation of B. influenzæ to influenza and to the complicating pneumonia. By some it is considered the primary cause of influenza, by others it is regarded as a secondary invader responsible for a certain proportion of the secondary pneumonias, and by still others it is not considered to bear any relation either to influenza or its complications.
A limited number of references to the extensive literature of the recent pandemic will amply serve to illustrate the various points of view that have developed.
Keegan[[32]] regards pneumonia as a complication and considers that B. influenzæ, the probable cause of influenza, is the primary cause of the pneumonia which may or may not be still further complicated by pneumococcus or streptococcus infection as a terminal event. Christian[[33]] states that epidemic influenza causes a clinically demonstrable bronchitis and bronchopneumonia in the larger proportion of cases, and lays particular emphasis upon the fact that it is quite incorrect to consider fatalities in the epidemic as due to influenza uncomplicated by bronchopneumonia. Blanton and Irons[[34]] speak of influenza as an “antecedent respiratory infection” of undetermined etiology, and believe that pneumonia when it occurs is due to autogenous infection by a variety of secondary invaders, principally of the pneumococcus and streptococcus groups. Hall, Stone, and Simpson[[35]] regard pneumonia strictly as a complication and quite distinct from influenza itself. Synnott and Clark[[36]] believe that the infection is characterized by a progressive intense exudative inflammation of the respiratory tract often terminating in an aspiration pneumonia with a variety of conditions found at autopsy and a multiplicity of secondary organisms responsible for the fatal termination. B. influenzæ was usually found but always with other organisms. Friedlander and his collaborators[[37]] speak of a fulminating fatal type of influenza with acute inflammatory pulmonary edema, but regard true bronchopneumonia as secondary, due to infection with pneumococcus or S. hemolyticus. B. influenzæ was not found more frequently than under normal conditions. Brem[[38]] and his collaborators present a clear cut clinical picture both of influenza and the secondary pneumonia to which it predisposes, regarding the latter as definitely due to secondary infection with pneumococcus, streptococcus or B. influenzæ, the virus of influenza being unknown. Ely[[39]] and his collaborators make no distinction between influenza and pneumonia, and apparently consider the epidemic due to a hemolytic streptococcus of indefinite and inconstant characters. The Camp Lewis Pneumonia Unit[[40]] states “the process [influenza], whether mild or severe, is etiologically and pathologically the same; * * *.” B. influenzæ was not found. In a report of The American Public Health Association[[41]] it is stated that deaths resulting from influenza are commonly due to pneumonias resulting from an invasion of the lungs by one or more forms of streptococci, by one or more forms of pneumococci, or by the so-called influenza bacillus. This invasion is apparently secondary to the initial attack. Wolbach[[42]] found B. influenzæ in a high proportion of cases, not infrequently in pure culture in the lung, and believes that there is a true influenzal pneumonia whether B. influenzæ is the cause of the primary disease or not. Spooner, Scott and Heath[[43]] isolated B. influenzæ in a high percentage of cases and consider it reasonable to suppose that it was the prime factor in the epidemic. Kinsella[[44]] found B. influenzæ infrequently and regards it as a secondary invader. MacCallum[[45]] regards B. influenzæ as a secondary invader and believes that it is responsible for a form of purulent bronchitis and bronchopneumonia following certain cases of influenza. Pritchett and Stillman[[46]] found B. influenzæ in 93 per cent of cases of influenza and bronchopneumonia. Hirsch and McKinney[[47]] state that B. influenzæ played no rôle in the epidemic at Camp Grant and apparently consider it due to a specially virulent pneumococcus.
No further references to the extensive literature of the recent pandemic seem necessary, since those cited above serve to illustrate the various points of view that exist. A similar diversity of opinion may be found in the reports from foreign sources.