Atypical Pneumonia*

The existence of cases of pneumonia distinct anatomically from lobar pneumonia or bronchopneumonia and possessing a correspondingly diverse clinical course and aetiology has, of course, been recognized for a number of years. The era of treatment of pneumonia with specific antipneumococcal sera seemed to coincide with the recognition of such cases as indicated by Rufus Cole (1936), and the twin characters of lack of response to therapy and an unusual radiographic appearance in the chest led to the separation of such " atypical " cases from the main group of the pneumonias. The use of the sulphonamide drugs only served to emphasize the unusual characters of atypical pneumonia, as even those sulphonamide derivatives active against the pneumococcus failed to influence its course. Then from 1938 onwards a number of authors in the U.S.A. (Reimann, 1938; Kneeland and Smetana, 1940; Longcope, 1940) published accounts of cases of atypical bronchopneumonia in young adults, some of which were of an unusual severity, though recovery was ultimately complete. These authors inclined to the view that they were in fact dealing with a new disease entity, though this view has since been challenged by others who consider that the widespread use of sulphonamides and, later, of penicillin has merely thrown the existence of unresponsive cases of atypical pneumonia into sharp relief. Meanwhile the wider use of radiology in the investigation of influenza-like illnesses led to the discovery that such cases often showed areas of lung involvement radiologically, though clinical examination had failed to indicate such changes. Gallagher, in 1934, thus reported a ,series of sporadic cases in preparatory-school boys in Pennsylvania and regarded the lung lesions as being instances of "pneumonitis." His later series of cases in Massachusetts in the year 1939 to 1940 (Gallagher, 1940) partook much more of the character of an infectious disease. About the same time, Bowen (1935) and Allen (1936), writing from U.S. Army stations, described radiologically similar cases of " pneumonitis" discovered among the hotchpotch of acute respiratory diseases seen in recruits and others during or even apart from outbreaks of socalled influenza. Thus the stage was set in the U.S.A. for *Read in opening a discussion at a combined meeting of the Sections of Medicine and of Pathology and Bacteriology at the Annual Meeting of the British Medical Association, Liverpool, 1950. a ready recognition of cases of acute respiratory disease with pulmonary lesions other than ordinary influenzal bronchopneumonia, when in 1942 and subsequently the opening phases of the war in America produced the inevitable wave of respiratory infections in Service establishments. The term "primary atypical pneumonia" thus sprang into existence and quickly displaced earlier terms, including that used by Scadding (1937) in describing a group of sporadic cases in England as " disseminated focal pneumonia." Towards the end of the war explosive outbreaks of atypical pneumonia in the Allied Armies in Italy renewed interest in the condition, particularly as these were the first instances of actual outbreaks in British troops, and the brilliant work of Robbins and his associates (1946) in discovering that these outbreaks were due to the rickettsia of Q fever, R. burneti, served only to emphasize the aetiological obscurity of the earlier cases. Though it must be clearly recognized that there are many respiratory-tract conditions in which a pneumonia atypical in course and character can be shown to exist, this paper is limited to a discussion of the syndrome of primary atypical pneumonia.