Legionellosis

Abstract

Legionnaires' disease was first recognized as a clinical entity following an outbreak of pneumonia that occurred among delegates to the American Legion convention in Philadelphia in 1976 (1). A total of 182 persons contracted pneumonia and 34 died. More than six months would pass before investigators from the Centers for Disease Control and Prevention (CDC) would isolate a previously unidentified bacterium from autopsy lung specimens. The bacterium was ultimately named Legionella pneumophila. Sera stored in CDC freezers from unsolved outbreaks of pneumonia revealed antibody seroconversion to L. pneumophila, suggesting that this was not a new disease. Retrospectively identified epidemics of Legionnaires' disease included outbreaks that occurred at the same Philadelphia hotel during a convention in 1974, an outbreak at a psychiatric hospital in Washington, D.C., U.S.A. in 1965 (2), and another at a meat-packing plant in Minnesota in 1957 (3). One Legionella species was isolated from specimens that dated back to 1947 (4).