With the knowledge that there is a prevailing epidemic of influenza and that the manifestations are largely in the respiratory tract, any pulmonary disturbance will necessarily make one suspicious of the presence or the oncoming of an influenzal pneumonia in the patient under consideration. The history of the onset, as of simple influenza, is the greatest factor. This with a continued temperature, cough, cyanosis, slow pulse, continued asthenia, or even an unusual leucopenia, may have a greater weight in determining the diagnosis of lung involvement than will the apparently definite or, as it may happen, the confusing chest signs. To differentiate from ordinary bronchitis, broncho-pneumonia and catarrhal pneumonia, one need only refer additionally to the severity and persistency of the disease when it is of the influenzal type, as compared with the mildness of the ordinary type. To differentiate it from croupous pneumonia, one need only compare the confusing symptom picture of the influenzal pneumonia with the definite, clear picture of ordinary pneumonia; or the confusing kaleidoscopic chest signs of the one with the definite, clear-cut signs of the other. The laboratory thus far has been the smallest factor in making the diagnosis, in that sputum examinations, blood examinations, blood cultures and urine examinations are mostly negative in their results, or at least the findings are not specific. We do not, however, mean to indicate that these tests are not of the greatest value. The leucopenia is the one outstanding feature which seems to have separated this infection from other acute lung infections, excepting miliary tuberculosis. The differentiation of influenzal pneumonia from an acute tuberculous process in the lung may be difficult, especially if there is no reliable history available. However, the fact that pulmonary tuberculosis usually begins at the apices of the lungs and influenzal pneumonia at the bases or at the apices of the lower lobes is quite helpful. Of course, the examination of the sputum for tubercle bacilli will be a deciding factor.
The differentiation between influenzal pneumonia and diseases of the pleura is one which practically rarely needs to be made, for there seem to be very few cases of influenzal infection of the lungs in which the pleura is not also involved to a greater or lesser extent.
Complications
In considering the complications of influenza one again comes up squarely against the question: What is influenza and what is the specific micro-organism responsible for it? If the Pfeiffer bacillus is the specific cause, what pathology can be attributed to it? It has been an almost universal observation that the lesions in the lungs and pleura which characterized the group of cases with lung involvement rarely yielded a pure culture of the Pfeiffer bacillus, and that secondly in a large percentage of cases the Pfeiffer bacillus apparently was absent, and that other micro-organisms, such as the pneumococcus, streptococcus, micro-organisms commonly found in the pneumonic processes, were present and predominated. The question arises, therefore, may not all the influenzas with lung involvement be complications of influenza? It is our feeling that Pfeiffer bacillus is present throughout the respiratory tract in all cases, and while it may of itself produce a lesion like a broncho-pneumonia or a lobar pneumonia, it chiefly prepares the soil for other germs which may happen to be present, and which are more commonly found in the pneumonias. We, therefore, look upon the lesion commonly found in the lung as being a part of rather than a complication of influenza, and look upon lesions elsewhere, due to the influenzal or other micro-organisms, as a definite complication.
There is no doubt that the most frequent complication of influenza, especially in the present epidemic, is in connection with the pleural membranes. When one recalls that pneumonia rarely occurs without there being also a pleuritis, and also when one recognizes that in an influenzal infection of the lungs the specific micro-organism, together with any other micro-organism which may happen to be present, seems to run riot, apparently abandoning its usual mode of invasion, it can be readily understood why this complication is so frequent and so varied. The pleurisy was usually of the fibrinous type, and rarely was accompanied with demonstrable fluid. Of the 153 soldiers in only 3 was fluid detected in the chest, and of the 394 civilians only 10 showed fluid. In many more cases fluid was suspected, but X-ray examinations and free needling of the chest showed that we had misinterpreted the physical signs.
After our experience in the epidemic of pneumonia in the spring of 1918, when the disease was also so prevalent in the cantonments, we of course expected to see many cases of empyæma and lung abscess in the present epidemic. In this we were agreeably disappointed. Only one case of empyæma and only one case with abscess of the lung were found up to the time of collecting our data and the compiling of our statistics. Both of these were among the civilians. From our experience since the compiling of our statistics, we are inclined to believe that this low incidence of empyæma may not altogether represent the real state of affairs, as we have since received in the hospital several cases of empyæma, as well as of abscess of the lung, which seemed to have followed an influenzal infection which had occurred three or four months previously. One of these cases was a particularly remarkable one, in that the patient had already been admitted to the hospital twice since his initial attack of influenza in October for suspected pleurisy with effusion. We were unable to find any fluid with the needle, though we felt certain of having demonstrated it a number of times physically and with the X-ray. About eight weeks after the second admission, however, pus was found after several needlings in the left chest, axillary space, apparently along the inter-lobar sulcus. This case was a good example of many we have seen in which a pneumonia, or possibly, as we see it now, a pleurisy, or even a localized empyæma, seemed to confine itself about the sulcus or fissure between the upper and lower lobes of the lung. Frequently the process began posteriorly, apparently at the apex of the lower lobe, and traveled forward and downward across the axillary space until it appeared in the anterior part of the chest. In most cases we interpreted our signs as those of a consolidated lung, and scarcely knew whether the consolidation was in the upper part of the lower lobe or in the lower part of the upper, or in both. In some cases we suspected a localized empyæma or an abscess in the sulcus, but in none did we find pus after exploring with the needle until this recent case occurred. The passage of the needle in this case, which was done several times before pus was found, always gave the impression that it was going through dense fibrous tissue for some distance before the abscess was finally found. From this experience, and from the extensive and irregular invasion of the pleura which we have seen demonstrated at autopsies, there can be no doubt that the clinical history of the complications of influenza in this epidemic is not a closed chapter.
In six patients there was a purulent inflammation of the pharynx, larynx and trachea. It was extensive and produced profound general symptoms, dyspnœa and profuse purulent expectoration. The lungs were clear, but the patient seemed for a time in danger of death. The condition was considered a grave complication. There was only one case of acute sinusitis, one case of antrum disease, and only four cases of middle ear infection were recognized. This is in marked contrast to other epidemics which have occurred to our knowledge in the past fifteen years or more, and which have been spoken of as influenza or “grippe.” Disease of the tonsils, middle ear disease, mastoid disease and sinus disease occurred with great frequency in those sporadic epidemics. This again seems to show that the deep respiratory tract was more generally and more severely affected in this epidemic than the upper respiratory tract.
With the exception of the pleura, the serous membranes were remarkably free from infection. Only one case of acute endocarditis, three cases of meningitis (all pneumococcic), none of pericarditis, peritonitis or arthritis were recognized among the 547 cases of influenza.
The kidneys did not seem to be involved in the infection. Albumen was present in the urine, as might be expected in febrile conditions, but no evidence of acute clinical nephritis, such as suppression of urine, general œdema or uræmia, was recognized. The condition of the urine in this epidemic will be described more in detail in another paper of this series.
A peculiar pathological process in the muscles was brought to our attention by Dr. Klotz, who demonstrated a myositis or hyaline degeneration of the lower end of the recti abdominalis. This lesion is carefully described in the pathological section. After our attention had been called to this lesion we recognized several cases clinically having the same condition. One was in the right sterno-cleido-mastoid muscle and another was in the left ilio-psoas muscle. This last patient while he was convalescing developed a severe pain in the left hip, extending upward into the lumbar region and downward into the thigh. His decubitus was like that of one suffering with psoas abscess. Every test available was made to confirm this diagnosis, but all the findings were negative. The patient rested in the hospital, in bed, for some time, gradually improved, and eventually made a complete recovery.