This progressive increase in virulence and invasiveness culminated in the explosive outbreak of the autumn wave of disease which reached epidemic proportions early in September and reached its peak in the following month. Again the increase in cases seems to have affected both the American Expeditionary Forces and the Army at home at very nearly the same time. The differences in incidence between the two main portions of the Army, that is, at home and in France, are shown in the general tables and charts. In this country the negro troops showed a relatively lower incidence at this time than before; indeed their admissions throughout this outbreak and their death rate during September were lower than that of the whites. The case fatality, however, in colored troops is consistently higher than that for white troops. Both races showed higher admission and death rates for the country as a whole in October than they did in September. The case fatality in whites was higher in September, while the October fatality was higher in the colored.

It is probable that it will never be definitely settled where the severe and fatal form of influenza arose in the fall of 1918. Each station, with few exceptions, claimed to be able to show that it owed its disease to transmission of infection from some previously affected point. Camp Devens, Mass., the first to report the highly fatal type of the disease,60 is supposed to have been infected from the city of Boston. The first cases there were on the naval receiving ship at Commonwealth Pier, August 28; thence the disease spread and soon infected the city. It is customary to think of all the subsequent influenza as having spread from this point and in many cases it is possible to trace this spread with some definiteness. There are some facts, however, that tend to the belief that there was a general increase of the activity of an already widely distributed virus which might have given rise to the fatal wave independently of infection from abroad.

61

Of these facts the first is that already mentioned, that from early August the influenza rates for the Army showed a progressive increase in geometrical ratio, the curve of rise plotting out on logarithmic paper as a practically straight line. (Chart XIV.) The second is the occurrence of definite outbreaks of increasing severity during the summer in this country and especially in the American Expeditionary Forces. These outbreaks ran right up to, if they did not indistinguishably blend with the great fall wave. The case of Camp Shelby, Miss., has been discussed. Camp Logan, Tex., is another camp whose outbreak appears to have been entirely independent of the Boston strain of virus, at least in its early stages. The disease appeared here just two days after its advent at Camp Devens, Mass. There is no known means by which the infection could have been transmitted from Camp Devens, and the disease did not make its appearance in the civil population of Texas for some time thereafter. The possibility of this outbreak having been due to a strain of the virus less virulent than that active in the Northeastern States is indicated by the fact that the fatality at Camp Logan was less than half that at Camp Devens and the further fact that the outbreak is recorded as having been of little severity until the receipt of recruits from the North already infected, who appeared to bring with them a more virulent infection. Camp Cody, N. Mex., had a similar experience in this respect.62

Another circumstance tending to support the view that the disease may have evolved its virulent type more or less generally throughout the world rather than that the virulent strain arose in one place and spread by contact, is the apparent impossibility of tracing this spread with any definiteness. As stated above, most stations regarded the disease as imported from without. In the American Expeditionary Forces it was felt that the severe influenza was brought from America. The first of the severe cases at Brest, France, for instance, occurred in a replacement detachment from Camp Pike, Ark., shortly after landing and while occupying a relatively isolated camp of their own.63 This detachment had left America late in July, 1918, and at a time when the incidence of respiratory disease was near its lowest here. The outbreak was of a severe type, with a high mortality, and for some time was limited to this detachment. Numerous reports of outbreaks in the American Expeditionary Forces during the severe wave express the belief that the disease was introduced by replacement troops from the United States.64 On the other hand, the general belief here was that the fatal influenza was introduced from Europe through the port of Boston. It is possible, of course, that neither view is correct, but that the fatal strain originated somewhere else and was introduced to both theaters nearly simultaneously. This is suggested by the report that a Norwegian vessel landed several severe cases in New York early in August, having suffered greatly from the disease on her voyage; however, there was no suggestion of fatal influenza in Norway at this time.65 The fatal type must have evolved somewhere from the less virulent variety. Its essential indentity with the latter is shown by the facts of immunity already recorded. It appears possible that this evolution might have occurred in many places at nearly the same time. An observation along this line is the fact that in several camps in the United States the outbreak of fatal influenza was preceded for several days by increasing incidence of mild cases gradually changing to the severe type. The introduction of a fully virulent virus from without would naturally be expected to produce fatal infections from the start. This transition is described for Camp Sherman, Ohio, as follows: 66

At the time the prevailing epidemic was at its height in New England numerous cases of coryza and bronchitis appeared at Camp Sherman. The picture was not characterstic of influenza, but the condition was so frequently noticed among patients at the base hospital that isolation was instituted and special wards set aside for this purpose. The absence of the usual features of influenza led to considerable comment as to the justification of such a diagnosis. This uncertainty was abruptly and definitely terminated by the sudden appearance of large numbers of patients exhibiting characteristics of clinical influenza. By September 24 the transition had occurred.

*

Somewhat similar observations are recorded for several other camps. These facts, then-the undoubted general distribution of the disease for months preceding the great outbreak and its progressive increase in prevalence and fatality from early in August, the difficulty of showing with any definiteness where the fatal type originated, and the suggestion in some reports of the development of a severe type locally from a milder strain-render it at least possible, and even probable, that the severe form arose not as a single strain but that many strains acquired increased virulence in different places at about the same time. The question remains unsettled, and more detailed studies of

future outbreaks will be required for its answer. Whichever view ultimately prevails, there can be no doubt that in many stations the disease was definitely introduced from without. Once introduced, the disease spread with characteristic rapidity and involved a large proportion of the command.

Table 27 shows the main facts of the epidemic for the large camps in the United States. It is impossible to give details of these outbreaks. The differences in incidence and fatality, as influenced by various factors, have already been discussed. It is desired, however, to describe the outbreak in one or two camps in order to give an idea of the conditions prevailing and of the difficulties faced, and to a great extent overcome, in the care and treatment of such enormous numbers of very sick men at one time.

TABLE 27.-Influenza and pneumonia. Admissions, deaths, and case fatality rates, for 40 large camps in the United States during the fall epidemic, 1918

"Arranged in order of mortality rate, influenza and pneumonia.

The outbreak at Camp Upton, N. Y., was studied and recorded in a way particularly valuable for epidemiological review.67 The report states that the disease was brought from Camp Devens, Mass., by troops from that station and began abruptly with the admission of 38 cases on the first day, September 13, 1918. It reached its peak October 4, with the admission of 483 cases, and

then rapidly declined. The following table shows the admissions by days for a period of seven weeks, the percentage of those admitted each day developing pneumonia, and the percentage dying. This classification is particularly valuable in that the cases admitted on a certain day are thus followed to their final disposition, and no allowance for the lag between admission and death is necessary, as is the case when deaths are recorded as of the day of occurrence. This table shows the abruptness with which the disease struck and gives an idea of the problem thrust upon medical authorities in the care of such numbers. It is noted that there is considerable irregularity in the figures for those developing pneumonia and dying. This daily variation is undoubtedly due to the fact that the disease attacked the organizations of a camp seriatim and that certain organizations contained more susceptible material than others. On the days when the admissions were mainly from susceptible organizations the resulting fatality was high, and vice versa.

Grouping the figures by weeks, an interesting relation is developed, thus: Epidemic of influenza at Camp Upton, N. Y. Admissions by days, and percentage of daily admissions developing pneumonia, and percentage dying

It is seen here that as the outbreak progressed the proportion of cases complicated by pneumonia increased, while the case fatality of the same cases became less. This was not due to any change in treatment or to any discoverable change in the bacteriology of the cases. As the whole series was studied by the same men, it is unlikely that differing standards of diagnosis have any bearing, as might often be the case in comparing figures from different sources. Unfortunately, this camp is the only one presenting its figures in such a way as

to allow this kind of a comparison, and it is not known whether this relation between pneumonia incidence and fatality holds generally or is only an accidental happening at Camp Upton.

The following account of the epidemic at Camp Grant, Ill., is introduced verbatim. Though Camp Grant stood fourth in the proportion of fatal cases during the epidemic, its proportion of admissions was not far above the average. It is thought that this account, written by the camp surgeon, will convey in a more satisfactory way than any other an idea of the character of this outbreak and of the difficulties besetting the course of the Medical Department in combating it.68

CAMP GRANT DIVISION SURGEON'S REPORT a

In the latter part of September a severe epidemic of clinical influenza attacked the camp, resulting in 10,713 cases of this disease during the months of September and October, with 2,355 cases of pneumonia and 1,060 deaths resulting.

The rapidity with which cases developed during the height of the epidemic promptly flooded the base hospital, and it became necessary to equip various infirmaries throughout the camp to receive patients. When the housing space in the infirmaries was filled, one or more contiguous barracks in each area were assigned for the reception of patients. All mild cases were received in the infirmary wards, and if the cases became more severe they were transferred at once to the base hospital. These wards were also used for the reception of convalescents returned from the base hospital, who were held for about a week for observation before being returned to duty. In addition to the observation and attention given the men in the infirmary wards by the surgeons of the various organizations, a medical officer of experience was detailed as visiting consultant. This officer visited each infirmary daily and gave his advice as to which cases should be transferred to the hospital.

The efficiency of the attention given in these wards is attested by the fact that although more than 2,000 cases were handled, but one death occurred in an infirmary and that man was a returned convalescent. As the number of convalescents multiplied, their care became a problem which was particularly acute on account of the lack of a detention or isolation camp. It was solved by granting furloughs to selected men after ascertaiming that their families were able and willing to give them proper care or supervision.

As the infirmary wards began to fill up with convalescents rather than acute cases, it was noted that many of these men had pronounced tachycardia. A cardiovascular specialist was detailed to visit all these wards and report on all cases having heart symptoms, with recommendations. This officer examined all convalescents returning from furlough and made recommendations as to their disposition.

The character of the complicating pneumonia during this wave of the influenza cycle differed only in degree from those observed earlier; the atypical pneumonias of the earlier months became the rule now and, especially in the first few weeks of the outbreak, there were noted cases with pneumonic symptoms of a fulminating character lasting 24 to 48 hours and showing post mortem a characteristic wet hemorrhagic condition with little or no evidence of inflammatory reaction. As noted above, a few cases of this type appeared in the spring wave. They will be described in more detail in the consideration of the pathology and symptomatology of the epidemic. In the later weeks of the outbreaks these fulminant cases became more rare, the fatal cases were ill a longer period of time, and the clinical and pathological conditions observed corresponded more closely with those seen during the preceding winter and spring. Empyema, so common then, was rarely seen in the early weeks of the fall wave, but in the

• See also Chap. XIV, Vol. V, of this history for a description of this epidemic in the base hospital.