Legionella in Shower Aerosols and Pontiac Fever Among Health Workers and Residents in Nursing Homes

Abstract

ISEE-275 Objective: Aerosols produced by the shower water flow can be contaminated by Legionella present in the hot water system. Material and Methods: Within the Legion' Air study, 828 elderly subjects residing in 34 nursing homes and 102 health workers were followed up during 4 months to ascertain incidence of symptoms associated with Pontiac fever. The exposure situation was inhalation of Legionella while showering or helping residents to take a shower. Water and air samples from 169 showers were taken at the end of the follow-up period and analyzed using the standardized culture and the fluorescence in situ hybridization (FISH) techniques adapted for Legionella. Sampling locations had been chosen after an audit of the hot water system in each home to assess exposure of all volunteers. We had previously proposed an operational definition of Pontiac fever (PF), for epidemiologic surveillance and investigation (Tossa et al, BMC Public Health. 2006;6:112). Results: Among residents, 29 cases of PF occurred [0.11 case/person- year; 95% CI (0.07–0.15)]. Using the same definition, 6 cases accrued among the personnel. Concentrations of greater than 105Legionella-FISH/L and 104Legionella-CFU/L in water were associated with an increased risk of PF (RR = 2.23, P = 0.05 and RR = 2.39, P = 0.11, respectively; P for trend <0.04). Concentrations above 103Legionella (CFU)/L in water were associated with an increased risk among health workers [RR = 4.8 (1.0–23.3)]. Incidence of PF among residents is associated with aerosol concentrations of above 103Legionella-FISH/L of air, underscoring that inhalation of aerosol is the true route of exposure. Conclusions: PF is a signal for the presence of Legionella bacteria and, consequently, for the risk of Legionnaire's disease, the severe form of the infection. These water and aerosol threshold values might be used in a view to protect against Legionnaire's disease.