Legionnaires' disease in non-Legionnaires. A report of five cases.

Seventeen patients with illness resembling Legionnaires' disease were evaluated for antibodies to the Legionnaires' bacillus. Three patients were Legionnaires who developed pneumonia after attending the July 1976 convention. All three were seropositive (titers greater than or equal to 1:128) to the Legionnaires' bacillus. None of the remaining 14 patients were Legionnaires. Five were seropositive and nine, seronegative (titers less than or equal to 1:32). The seropositive patients had illnesses best explained by Legionnaires' disease, whereas the seronegative patients had illnesses better explained by other diagnoses. This correlation between serology and clinical findings supports the specificity of the antibody test for Legionnaires' disease. Of the five non-Legionnaire seropositive cases, two occurred before, and one 3 months after, the convention. The case histories of these five patients are presented. Disease generally involved the lungs, kidneys, and the central nervous system. Although the pathogenesis of this multiple organ involvement is unclear, a possible explanation is the production of a toxin by the Legionnaires' bacillus.