Subclinical Legionella infection in workers near the source of a large outbreak of legionnaires disease

A survey was conducted of exhibitors at a 1999 floral trade show, where a w hirlpool spa on display caused a large outbreak of legionnaires disease (LD ). In total, 742 exhibitors without LD returned a questionnaire on their wh ereabouts during the fair and their health afterward and supplied blood sam ples for the detection of IgM and IgG antibodies against Legionella pneumop hila. The exhibitors had higher average antibody levels than did the genera l population. The closer to the whirlpool that the exhibitors worked, the h igher their antibody levels. Both high-normal and high titer levels were fo und more frequently among workers with more exposure, suggesting that seros urveys among potentially exposed subjects are a valuable tool for outbreak investigation. Some differences in health complaints were observed between the more and less exposed groups, as estimated by the workplace location, b ut few differences were found between groups with different antibody levels .