Outbreak of Legionnaires' disease associated with a display whirlpool spa

Background Recognized outbreaks of Legionnaires' disease (LD) are rare; whe n they occur, they provide opportunities to understand the epidemiology of the illness and improve prevention strategies. We investigated a population -based outbreak. Methods After the confirmation of LD in October 1996 in five people in neig hbouring towns in southwest Virginia, active surveillance for additional ca ses was undertaken. A case-control study was conducted to identify exposure s associated with illness, followed by a cohort study among employees of th e facility at which the source of the outbreak was located in order to asse ss unrecognized exposure and illness. Samples of likely sources of LD in th e facility were cultured for Legionella. Results In all, 23 laboratory-confirmed cases of LD were eventually identif ied. Of the 15 cases in the case-control study, 14 (93%) reported visiting a home-improvement store, compared with 12 (27%) of 45 controls (matched od ds ratio [MOR] = 23.3; 95% CI: 3-182). Among home-improvement centre patron s, 10 (77%) of 13 cases questioned recalled either visiting or walking by a display whirlpool spa, compared with 3 (25%) of 12 controls (MOR = 5.5; 95 % CI : 0.7-256.0). Two cases' sputum isolates were an exact match, by monoc lonal antibody subtyping and arbitrarily primed polymerase chain reaction, to a whirlpool spa filter isolate from the store. Employees reporting more exposure to the display spas were more likely to report symptoms of LD or t o have an elevated titre. Conclusions This investigation shows that LD can be transmitted from a whir lpool spa used for display only, and highlights the need for minimizing the risk of transmission of LD from all water-filled spas.