Effect of immunosuppressive therapy on the clinical presentation of legionellosis.

To determine whether the clinical course of legionellosis in patients treated with immunosuppressive agents differs from that seen in other patient groups, data on 52 Finnish patients with legionellosis confirmed by culture or by the direct immunofluorescent antibody test was reviewed. Of these patients 44% were immunosuppressed, 23% had other underlying diseases and 33% had no predisposing conditions. Among those without predisposing conditions, only Legionella pneumophila serogroup 1 was observed, whereas among the immunosuppressed patients, serogroup 6 dominated. Legionellosis was nosocomial in 73% of the immunosuppressed patients and in 33% of the patients with other underlying diseases but was travel-associated in 76% of those without predisposing factors. The case fatality rate (37%) was high but was not associated with preceding immunosuppression. These results indicate that although the serogroups and the sources of legionellosis differ in immunosuppressed patients compared with other groups, the clinical presentation is not more severe.