Legionella species infection in adult febrile respiratory tract infections in the community.

Legionella spp. (Lsp) are well recognized as etiologic factors in pneumonia but less so in respiratory tract infections (RTI) in the community. The objective of the present study was to characterize febrile RTI patients with a documented Legionella etiology, in terms of specific serogroups, clinical manifestations of the disease, disease course and the effect of antibiotic therapy. Ambulatory adults with febrile RTI (n = 250) were included in a prospective study in which the etiological causes of the infection were identified using sophisticated serological techniques. Paired sera were obtained for each of the patients and were tested for 41 different serotypes of Lsp using micro-immuno-fluorescence (MIF) serology. Only a significant change in IgG and/or IgM antibody titers was considered diagnostic. In 28 patients (11.2%) there was serological evidence of acute infection with 1 of the types of Lsp. The infections were manifested clinically as upper RTI in 9 patients and as lower RTI in the other 19 patients (community-acquired pneumonia in 2 of these). L. pneumophila serogroup 1 was identified in 3 patients, L. pneumophila serogroups higher than 1 were identified in 13 patients and L. non-pneumophila serogroups in 18 patients. The clinical and laboratory findings in patients with acute Lsp infection were not significantly different from those in patients without evidence of this infectious agent. The length and course of the disease were similar in the 12 patients treated with specific antibiotics for Lsp and in those who were not. We conclude that Lsp can be identified in a significant percentage of patients with acute febrile RTI. No specific clinical or laboratory features were observed for these patients and specific antibiotic therapy does not affect the course of the disease.