STUDIES ON INFLUENZA IN THE PANDEMIC OF 1957-1958. II. PULMONARY COMPLICATIONS OF INFLUENZA*†

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Abstract
Exhaustive studies on 33 patients admitted with the pulmonary complications of influenza during the pandemic of 1957-1958 are reported. Four distinct clinical and laboratory syndromes were recognized (1) Patients with transient pulmonary signs without roentgenographic evidence of pneumonia. These patients did not have bacterial infection and recovery was prompt on symptomatic treatment alone. (2) Patients with secondary bacterial pneumonia arising late in the course of influenza. These pneumonias were predominantly produced by pneumococci; the course of the infection and response to therapy did not differ materially from that of uncomplicated bacterial pneumonia in the absence of influenza. (3) Patients with laboratory and clinical evidence of combined influenza virus and bacterial infection. In these patients the infection was severe. Despite adequate antibacterial therapy, 3 patients died during their acute illness, one with pneumococcal and 2 with staphylococcal infections. Influenza virus was isolated from the lungs of all 3 in association with bacteria. (4) Six patients studied developed a fulminating, diffuse, hemorrhagic pneumonia which led to death in 5. No pathogen other than the influenza virus could be related to this abacterial syndrome. The course was characterized by extreme dyspnea, cyanosis, hypoxia, and failure to respond to antibacterial drugs. Influenza virus was isolated in high titer from lungs. The importance of chronic underlying disease in the serious pulmonary complications of influenza was stressed. Twenty-one of 30 patients with roentgenographically confirmed pneumonia had pre-existing illness or pregnancy. Fourteen of these 21 had underlying cardiac disease which was of rheumatic origin in 10. This article and a review of recent and earlier literature supports the belief that: (a) influenza virus infection per se may induce pneumonia in the absence of other microbial pathogens; (b) underlying disease, and most particularly rheumatic heart disease, may be important in the genesis of influenza virus pneumonia.