It would appear that much of the divergence of opinion that has been formed has depended to a considerable extent upon the conditions under which cases have been observed. This is clearly brought out by contrasting the experience of Fantus[[39]] dealing with private cases in civilian practice, where pneumonia was relatively uncommon, with that of others dealing only with cases in large hospitals, where those admitted have been in large part selected seriously ill patients with a high incidence of pneumonia, the milder cases comprising from 60 to 90 per cent of those attacked by influenza never reaching the hospital. Variations in opinion with respect to the bacteriology of the epidemic, especially in regard to B. influenzæ, would appear to be due for the most part to differences in bacteriologic technic, in some degree to differences in interpretation. Accumulating evidence can leave little doubt that B. influenzæ was at least extraordinarily and universally prevalent throughout the period of the epidemic and thereafter, and that earlier reports of failure to find it were due to the use of methods unsuitable for its detection and isolation.
The opportunity afforded the commission at Camp Pike to devote their full time to a systematic and correlated group study of the epidemic simultaneously from many aspects throughout its whole course made it apparent that influenza per se is in the large majority of instances, in spite of the initial picture of profound prostration, a relatively mild disease which tends to rapid spontaneous recovery. This opinion is supported by the fact that the disease during the first waves of the epidemic in this country, which it is now recognized occurred pretty generally in the army camps during the spring of 1918, was so mild that it attracted only passing attention, since the disease at that time was not sufficiently virulent to predispose to any alarming amount of pneumonia. With the return of the epidemic in the late summer and early fall, however, the disease had attained such a high degree of virulence that it predisposed to an appalling amount of severe and often rapidly fatal pneumonia, which often detracted attention from the real nature of the preceding disease. Yet even during the fall epidemic from 60 to 90 per cent of the cases of influenza proceeded to rapid recovery without developing complications. On this ground alone it would seem only logical to regard pneumonia strictly as a complication of influenza rather than as an essential part of the disease, irrespective of whether the pneumonia may be caused by the primary cause of influenza or not. The complexity of the clinical features, the bacteriology and pathology of the pneumonias following influenza lend further support to this opinion.
It seems better, therefore, to consider influenza first as a disease by itself and subsequently to take up the question of pneumonia and the relation of influenza to it.
The most striking clinical features of influenza are its epidemic character, its involvement of the respiratory tract, its extremely prostrating effect, and the often surprising rapidity with which the individual cures himself. These features strongly suggest that the etiologic agent of the disease is an organism subject to rapid changes in virulence; that it is confined to the respiratory tract where it produces a superficial inflammatory reaction giving rise to the characteristic symptoms of coryza, pharyngitis and tracheitis; that it elaborates a poison, possibly a true toxin, readily absorbed by the lymphatics, the effect of which is manifested in the profound prostration, severe aching pains, erythema, and leucopenia; and that it may either disappear promptly from the respiratory mucous membrane at time of recovery or may persist, leading a relatively saprophytic existence for an indefinite period of time, being no longer harmful to the individual, at least more than locally, because of an acquired immunity. Furthermore, in our opinion, the very brief incubation period suggests that the disease is bacterial in origin, rather than that it is analogous to the exanthemata, the majority of which present a comparatively long, fairly constant, incubation period.
B. influenzæ has characteristics in accord with the clinical features of influenza. It is an organism of very labile virulence; it is always present in our experience on the mucous membranes of the respiratory tract in early uncomplicated cases of influenza, often in overwhelming numbers; in only very exceptional instances, in adults at least, does it invade the body producing a general infection, as the numerous reports of negative blood cultures testify; recent investigations by Parker[[48]] and others indicate that it is capable of producing a toxin quickly fatal for rabbits; it is predominantly present in the respiratory tract during the active stage of the disease and disappears in a considerable proportion of cases at time of recovery, while in others, more particularly those that develop an extensive secondary bronchitis and bronchiectasis it may persist for an indefinite period of time.
It is, of course, fully appreciated that the foregoing is in the main merely argumentative reasoning and it is put forth only to suggest that B. influenzæ merits a much closer scrutiny with respect to its etiologic relationship to influenza than the trend of present opinion has awarded it.
Although there remains some difference of opinion as to the relation of influenza to pneumonia, the majority of observers concur in regarding pneumonia as a complication and this would seem to be the only logical interpretation of the facts available. The same may be said with respect to purulent bronchitis and bronchiectasis. It is of considerable significance in this connection that pneumonia following influenza presents no uniform clinical picture, no uniform bacteriology and no uniform pathology. Whether the predisposition of patients with influenza to contract pneumonia is preponderantly due to lowering of general resistance to infection by the extremely prostrating effect of the disease and the inhibition of leucocytic defense, or to a destruction of local resistance against bacterial invasion by reason of profound injury to the bronchial mucosa, or to a combination of both factors, is difficult to say. It seems most probable that both are concerned. At any rate it seems clear that in the presence of influenza a considerable variety of organisms which under ordinary conditions do not find lodgement in the lungs are able to gain access to the lower respiratory tract and produce pneumonia.
CHAPTER III
SECONDARY INFECTION IN THE WARD TREATMENT OF INFLUENZA AND PNEUMONIA
Eugene L. Opie, M.D.; Francis G. Blake, M.D.; James C. Small, M.D.; and Thomas M. Rivers, M.D.
One of the most pressing problems that presented itself in the care of influenza and pneumonia patients in the army cantonments during the recent epidemic was the danger of secondary contact infection because of the overcrowding of the base hospitals, nearly all of which were taxed far beyond the limits of their capacity. That this danger was very real was fully demonstrated by certain studies in ward infection that this commission was able to make at Camp Pike[[49]]. It is the purpose of the present section of the report to present these studies and to discuss the means whereby this danger may be most successfully met.