A whirlpool associated outbreak of Pontiac fever at a hotel in Northern Sweden

In April 1999, an outbreak of Pontiac fryer occurred at a hotel in Northern Sweden. A retrospective cohort study to find the source and define the ext ent of the outbreak was carried out among 530 Swedish and Norwegian guests. Twenty-nine epidemiological cases (8 % of 378 responders) aged 21-57 years were identified. Antibodies against Legionella micdadei were detected in 1 7 of 27 tested cases and 3 other symptomatic persons. Visiting the whirlpoo l area was identified as the sole risk factor (RR 86; 95% CI 21-352) and in fected cases were confined to visitors to this area over three successive d ays. The attack rate was 71% (27/38) and 24 cases (83 %) used the whirlpool . Environmental sampling was negative for Legionella sp. But epidemiologica l investigation strongly suggests that the whirlpool was the source of the outbreak. The possibility of serious legionella infections underlines the i mportance of strict maintenance practices to maintain hygiene of whirlpools .