1. Consideration of all the evidence available makes it seem highly probable that B. influenzæ is the specific etiologic agent of epidemic influenza, because (a) it is always present in early uncomplicated cases of influenza; (b) it is predominantly so during the acute stage of the disease in cases going on to rapid recovery without development of complications; (c) its presence in varying numbers in normal individuals and in other diseases of the respiratory tract is not valid evidence against its etiologic relationship to influenza, but on the contrary is quite in harmony with what should be expected from our knowledge of other bacteria known to be the etiologic agents of various respiratory diseases; (d) its rapidly increasing prevalence in normal individuals simultaneously with the progress of the epidemic indicates that actual dissemination of B. influenzæ readily occurs and is very widespread during pandemic times; (e) cultures of B. influenzæ freshly isolated from early acute cases of influenza are pathogenic for animals, and may produce in monkeys a disease closely resembling influenza.
2. Final proof of the exact relationship of B. influenzæ to influenza must depend upon (a) more definite knowledge of the immunology both of the organism and of the disease, and (b) knowledge of the pathologic lesions of influenza and the production of these lesions in animals by inoculation with B. influenzæ.
CHAPTER II
CLINICAL FEATURES AND BACTERIOLOGY OF INFLUENZA AND ITS ASSOCIATED PURULENT BRONCHITIS AND PNEUMONIA
Francis G. Blake, M.D., and Thomas M. Rivers, M.D.
The material presented in this section of the report consists of clinical and bacteriologic observations made during the course of an investigation of influenza and its associated bronchitis and pneumonia at Camp Pike, Ark., between September 6 and December 15, 1918, comprising part of a correlated study of the epidemiology, bacteriology, pathology, and clinical features of these diseases. The bacteriologic studies are in the main limited to those made during life, those made at necropsy being reported in another section of this report.
Methods.—All cases upon which the clinical and bacteriologic data presented are based, were examined by the authors and our own clinical histories and physical examinations were recorded. This was considered of special importance, since in studying a group of diseases in which secondary infection of the respiratory tract might supervene at any time, it was essential to determine as far as possible the exact clinical condition of the patient at the time when bacteriologic examinations were made. The bacteriologic methods employed were the direct culture of nose and throat swabbings and of selected and washed specimens of sputum on the surface of 5 per cent defibrinated horse blood agar plates, the intraperitoneal inoculation of white mice with specimens of sputum according to the method described by Blake[[28]] for the determination of pneumococcus types, and in some cases the method of Avery.[[29]] B. influenzæ pneumococci and hemolytic streptococci were identified by the methods described elsewhere. Note was made in most instances of the presence of other organisms such as members of the Gram-negative diplococcus group, staphylococci, diphtheroids, and members of the streptococcus viridans group, but no attempt was made to further isolate or identify them since they played no significant part in the cases studied except in rare instances.
Influenza
The fall epidemic of influenza at Camp Pike began about September 1, 1918, and reached epidemic proportions on September 23 when 214 cases were admitted to the base hospital. The epidemic was at its height from September 27 to October 3, during which period there were in the neighborhood of 1,000 new cases daily. From this date until October 31 the number of new cases occurring daily steadily decreased and by the latter date the epidemic was over. Scattered cases continued to occur, however, throughout November, and during the last week of this month and the first week of December a second epidemic wave of relatively mild character occurred. From September 1 to October 31 the total number of cases of influenza reporting sick was 12,393. During the same period there were 1,499 cases of pneumonia with 466 deaths.
Influenza as observed at Camp Pike differed in no essential respects from that occurring elsewhere. In brief, it presented itself as a highly contagious, self-limited infectious disease of relatively short duration in most instances, the principal manifestations of which were sudden onset with high fever, profound prostration, severe aching pains in back and extremities, conjunctival injection, flushing of the face, neck, and upper thorax often amounting to a true erythema, and a rapidly progressing attack upon the mucous membranes of the respiratory tract as manifested by coryza, pharyngitis, tracheitis and bronchitis with a marked tendency to hemorrhage; in itself it is rarely serious, but in reality serious because of the large number of individuals attacked and temporarily incapacitated and because it predisposed to widespread and highly fatal secondary infection of the lungs.
Clinical Features.—A clinical study of 100 consecutive cases of influenza admitted during the height of the epidemic was made.