Amberson and Peters, as well as Minor, take sharp exception to the statement of Fishberg, and the former have collected the evidence against Fishberg’s view. They first point out that a comparison of the incidence of 5.4 per cent. among hospitalized tuberculous patients at Chicago cannot be compared with a much higher incidence of the epidemic in the various military camps. As Heiser has pointed out, the mere quartering of men in barracks seems to have a tendency to increase the risk from acute respiratory diseases. Furthermore, the incidence at some sanatoria was low, while at others it was high, nearly as high as for the community at large. In Hawes’ report of the epidemic among the Massachusetts sanatoria, Lakeville had escaped entirely, while Rutland which consisted chiefly of ambulatory cases, less easily controlled, had an influenza incidence of 18.3 per cent. among the patients, and 21.3 per cent. among the employees. At Montefiore Home, the proportion of tuberculous patients and employees contracting the infection was practically the same as among the nontuberculous employees, and about the same percentage of both groups developed evidence of bronchopneumonia.
Still another fallacy in the comparison of incidence in institutions and the like is proven by the work done by Jordan, Reed and Fink, who found that in the various Chicago telephone exchanges the attack rate varied from five per cent. to twenty-seven per cent., although the working conditions were approximately the same. The attack rate in one section of the students’ army training corps in Chicago was 3.9 per cent., while in another section particularly exposed to infection it was 39.8 per cent. Similarly Frost found the incidence in Louisville, Kentucky, to be 15 per cent., and in San Antonio, Texas, 53.3 per cent. All these figures show the difficulty of comparing rates for various institutions and various groups of individuals. Although Fishberg quoted Rickmann in support of his contention that influenza has no effect whatever upon tuberculosis, Amberson and Peters used his work in support of their contention, and call attention to the fact that in thirty out of forty tuberculous persons reported by him who had contracted the grip, the attack did not produce any aggravation of the lung condition. Presumably it did in the other ten. If even 25 per cent. of tuberculous patients who contract influenza have their pulmonary condition aggravated, this should be regarded as a notable number. According to Stivelman, 11.4 per cent. of tuberculous influenza cases died at Montefiore Home. In a survey of convalescents from the Loomis Sanatorium, Amberson and Peters found that seventy had contracted influenza, or 5.7 per cent. of the number surveyed, and that 11.4 per cent. of these had had relapses of their pulmonary condition, apparently due to the acute disease, while 22.9 per cent. had died from the intercurrent infection. 2.8 per cent. were deaths due to tuberculosis after convalescence from the influenza.
Tubercle bacilli have been found in the sputa of convalescent grip patients, whose sputa had previously been negative, by Amberson and Peters, as well as by Berghoff, at Camp Grant. The latter found that 50 per cent. of his cases showed a reactivation and a positive sputum after an attack of influenza.
Amberson and Peters agree with Fishberg in the observation that there has been no increase in the general mortality from tuberculosis within the recent months, and suggest as an explanation the possibility that during the epidemic enough of the old cases were carried off to account for a temporary lull until new cases developed, or others had time to reach later stages of the disease. As we have previously remarked, Leichtenstern observed this same phenomenon following the 1889–1890 epidemic.
The state of our knowledge of influenza and tuberculosis is considerably clouded by divergent opinions such as those quoted above. To further complicate the picture, there are other authors who assume a middle ground and believe that there is some truth in both lines of contention. Thus, Amelung believes that the morbidity among patients with pulmonary tuberculosis is slight, and that the grip takes a milder course in such patients than in the nontuberculous, unless the disease is far advanced, but that pulmonary tuberculosis may and sometimes does follow the disease in patients whose lungs were previously sound, and that in the last mentioned cases the prognosis is relatively bad. Peck finds that in some tuberculous patients the disease has been aggravated, but in the majority the intercurrent influenza did not appear to have been the causative factor in the acute exacerbation of the tuberculosis.
Debré and Jacquet have reviewed the European literature on the subject pro and con, and though they admit that there are exceptions, as at l’hôpital Tenon, where, in a barracks reserved entirely for female tuberculosis patients there was a veritable epidemic of grip, 29 per cent. of the twenty-eight being attacked in a few days; and at the sanatorium de La Tronche, where 83 per cent. took ill between the 25th of September and the 20th of October; they conclude that as a rule tuberculous individuals are less heavily attacked by the influenza than are the nontuberculous. As they suggest, the first explanation that comes to mind is that the tuberculous are isolated in the hospitals where general hygienic conditions are good, but we have all seen other institutions, hospitals, etc., in which the inmates were not spared as they were in tuberculosis hospitals. Furthermore, in certain sanatoria, such as the sanatorium of the Côte Saint-André, and Bligny, and several German sanatoria, the proportion of tuberculous individuals attacked was very much less than that of the professional attendants, the physicians and nurses. Again, where cases have occurred in these hospitals, and little precaution was taken to prevent its spread, very few other individuals took sick. Finally, many have noted the infrequency of the disease even in those tuberculous individuals who were living at home. It has been suggested that rest in bed from the beginning of the attack explained the mildness, or that the immunity resulting from the infection with pneumococcus, streptococcus, etc., in tuberculous individuals explained the absence of pulmonary complications. Marfan, who observed this same phenomenon in 1890, suggested that it might be due to a refractory state of the tubercle bacillus against the virus of influenza. Debré and Jacquet conclude that none of these explanations is satisfactory.
Having concluded that tuberculosis does protect in some measure against influenza, Debré and Jacquet next discuss whether the latter has increased the severity of tuberculosis in the subjects who were already tuberculous. They review the literature and make their conclusions, not from statistical records, but from general observations. They consider first those cases of phthisis which are open cases when attacked, and second, latent tuberculosis. Their conclusion concerning the first group is that influenza does not have any effect on the rapidity of evolution of the tuberculous process, except in very rare instances, such as an occasional case of miliary tuberculosis following grip. As regards latent tuberculosis, however, they do believe that the intercurrent acute infection does cause in many cases a lighting up of a previously entirely dormant tuberculosis. It seems rather difficult to reconcile the two ideas. If one type of tuberculous individual is rendered more susceptible to the ravages of consumption, it would seem reasonable to expect that all types would be so affected.
The greatest difficulty in reaching a conclusion regarding the effects of influenza on tuberculosis, and vice versa, is due to the fact that the individuals studied are in all stages of the disease, and that each individual reacts differently and in his own way. Opinions have been based chiefly on clinical observations, and not on statistical study of large series of cases, while from the nature of the conditions, even statistical studies would not be without great fallacy.
Armstrong, found in a survey made in Framingham, Massachusetts, that 16 per cent. of the entire population was affected with influenza, but only 4 per cent. of the tuberculous group in the community. Most of these latter were of the arrested type and were going about taking their part in industry and exposed to the same degree of contact as was the case with the normal population. The fatality rate was equally in contrast. Armstrong concluded that there appeared to be a relative degree of protection for the highly tubercularized. If we accept these figures at their face value we must conclude then either that tuberculosis offers some degree of protection against acute influenzal infection, or, that the tuberculous of Framingham have been so well trained in sanitation and personal hygiene, as a result of the Framingham demonstration, that they have been able to protect themselves against the grip. In the latter case we must look upon the result as a successful demonstration of the principles of preventive medicine. Certainly this did play a part, to the extent at least that individuals knowing themselves to be infected with tuberculosis, and knowing themselves to be in the presence of a pandemic, became more wary of crowd contact, and in case they did become ill, they undoubtedly went to bed at the earliest opportunity.
If, on the other hand, this is a true demonstration of relative immunity in a chronically infected individual, the explanation must be sought elsewhere. Does a chronic respiratory infection confer a relative degree of immunity to an acute respiratory disease? Do the germs already on the premises exert, so to speak, “squatters’ rights?” Are we observing an example of non-specific immunity due to local preceding infection? Still another factor may play an important role, the factor of race stock. The excess of tuberculosis in negroes, for instance, over that in whites, is in some localities double or treble, while various observers, as Frost, Brewer, and Fränkel and Dublin, report that the influenza incidence and mortality among negroes was decidedly less than that among the whites. Winslow and Rogers found that in Connecticut the proportion of influenza-pneumonia deaths is lower than would be expected among persons of native Irish, English and German stock, and higher than was to be expected among Russian, Austrian, Canadian and Polish stock, while it was enormously high among the Italian. Italians are notably insusceptible to tuberculosis, while the Irish are much more prone to infection with the disease. For example, in Framingham, where the tuberculosis incidence rate for the entire population was 2.16 per cent., the rate in the Italian race stock was 0.58 per cent., and in the Irish, 4.80 per cent. In Framingham there was about four times as much influenza among the Italians as among the Irish. Is this apparent insusceptibility of certain race stocks an inherent condition, or is it dependent chiefly on differences in living conditions and in age prevalence in the different races? Probably it is chiefly the former. Frost, for instance, found that among the negroes the incidence of influenza was lower even though the living conditions were much poorer than those among the whites.