Epidemic Respiratory Disease: The Pneumonias and Other Infections of the Repiratory Tract Accompanying Influenza and Measles

The bacteriologic studies in cases of influenza described in this report fully support Pfeiffer’s claim that B. influenzæ is invariably present in the disease. It is particularly important to note that these results were obtained in early uncomplicated cases of influenza and are not dependent upon cultures made from cases complicated by pneumonia or obtained at autopsy. In view of this fact the tendency so apparent in much of the recent literature to relegate B. influenzæ to a place of secondary or minor importance in the disease seems hardly justifiable. It would seem that this tendency is largely dependent upon three factors: first, the failure of many to find B. influenzæ either during life or at autopsy in any considerable proportion of cases; second, the frequent failure to draw a clear distinction between influenza itself and the pneumonia to which it predisposes with a consequent overemphasis upon autopsy bacteriology where a considerable variety of secondary organisms have attracted particular attention; and third, an incorrect interpretation of the undoubtedly large number of B. influenzæ carriers found among normal individuals and those with other diseases during the period of the epidemic and to less extent in interepidemic times.

Since the majority of workers who are thoroughly familiar with the technic of cultivating B. influenzæ have encountered little difficulty in finding it in a large majority of cases, it is felt that the considerable number of negative reports that have appeared can depend only upon the unfamiliarity of those who have failed to find it with the proper bacteriologic methods. This is quite apparent in many of the reports that have been published, and is not surprising in the face of the excessive demand for well-trained bacteriologists occasioned by the war.

One important feature in the successful isolation of B. influenzæ from all cases that has been brought out in the course of the work here reported, is the necessity of making simultaneous cultures from all portions of the respiratory tract, since by no single culture method was it found possible to find the organism in all cases. It has been pointed out that one of the most characteristic local phenomena of the disease is the rapidly progressing attack upon the mucous membranes of the respiratory tract. It seems quite possible that B. influenzæ in predominant numbers at least may be found in many cases only at the crest of the wave, if we may speak of it as such. By way of analogy is the well-recognized fact that the successful isolation of streptococcus from cases of erysipelas often depends upon taking cultures from the margin of the advancing lesion. While definite proof is lacking for this opinion, it would seem to receive some support from the observation that B. influenzæ rapidly disappears from the throat with the onset of convalescence in a considerable proportion of cases. It is felt that these observations, establishing the predominance of B. influenzæ in the early acute stages of the disease, are of considerable significance, especially when exactly the reverse condition was found in studying the incidence of the organism in cases of measles.

In consideration of the primary cause of influenza, attention has often been focused upon the many different bacteria found in autopsy cultures. The most prominent of these are the ill-defined diplostreptococci of the European writers, the various immunologic types of pneumococci, and S. hemolyticus. Other microorganisms less frequently found are staphylococci, M. catarrhalis, nonhemolytic streptococci, and B. mucosus capsulatus. It is not within the scope of this paper to discuss their relation to the various types of pneumonia found at autopsy, but their very multiplicity would seem sufficient prima facie evidence that they bear no etiologic relationship to influenza and must be regarded only as secondary invaders. If any further support for this opinion were necessary, it may be found in the studies upon the incidence of pneumococcus and S. hemolyticus in early cases of influenza described in this report. Both were found to occur in the same proportions in which they may be found in normal individuals at any time.

Although Pfeiffer maintained that B. influenzæ was found only in true epidemic influenza, the incorrectness of this contention has been thoroughly established by many reliable investigators and it has been shown beyond question that influenza bacilli may always be found in a small proportion of normal individuals and are not infrequently found in other respiratory diseases.

The fairly extensive study that has been made of the incidence of B. influenzæ in normal men and in cases of measles has clearly demonstrated that the proportion of carriers found in any group depends upon the prevalence of influenza in the group studied and that with the progress of the epidemic the percentage of carriers has steadily increased. When one considers that the opportunity for the dissemination of B. influenzæ by contact infection is almost unlimited during an epidemic of the proportions of that which has swept over the country, this is not at all surprising. That such a large number of normal individuals became carriers of B. influenzæ during the epidemic would seem to be sufficient evidence that actual dissemination does occur and to controvert the theory that in actual cases of influenza, conditions are established in the respiratory tract whereby B. influenzæ, always present in small numbers, is enabled to “grow out” and become the predominant organism. From a consideration of all the observations made as to the incidence of B. influenzæ in various conditions it would appear that the carrier condition is quite analogous to that found with many other bacteria, and may be divided into three groups: (a) acute carriers, those having influenza, (b) contact carriers, those who during epidemic times become temporary carriers of the organism without contracting the disease, and (c) chronic carriers, the relatively small number of normal individuals or those with chronic respiratory conditions who carry B. influenzæ over long periods of time. From the facts at hand this would seem to be the most probable explanation of the conditions found. It is certainly true that the established presence of pneumococcus, B. diphtheriæ, meningococcus and many other organisms in a varying proportion of normal individuals is not regarded as sufficient evidence to exclude them as the etiologic agents of the diseases which they cause.