Legionnaires' disease outbreak associated with a cruise liner, August 2003: epidemiological and microbiological findings

Abstract

Eight cases of Legionnaires' disease were identified among the 215 German passengers after a cruise to the Nordic Sea in August 2003. An unmatched case-control study was conducted to identify risk factors and the source of infection. In total, eight passengers fulfilled the case definition, one of these died. Forty-two passengers served as controls. The attack rate was 4%. The mean age was 60 years for cases and 62 years for controls. Prolonged exposure to the spa pool seemed to be a risk factor of infection (OR 4.85, P=0.09). Legionella pneumophila serogroup 1, monoclonal antibody (mAb) subgroup 'Knoxville' was isolated from clinical and environmental samples. DNA sequence-based typing revealed that these isolates were indistinguishable from each other. The investigation showed the importance of an interdisciplinary approach of microbiology and epidemiology as not all sites on the ship that tested positive for L. pneumophila actually posed a relevant risk for the passengers.

Fig. 1

Epidemic curve of the Legionnaires' disease outbreak on a cruise ship in August 2003. ■, Confirmed cases;, suspected cases.

Fig. 2

Age distribution of confirmed cases (■), suspected cases (□) and controls ().

Fig. 3

Bridge Deck (stern): schematic of spa pool area and representation of passengers' duration of stay close to the spa pool as reported in the self-administered questionnaire. Symbols are arranged in groups and do not represent the real position of a person on board the ship. Symbols on the spa pool line indicate that these persons used the spa and in addition spent some time close to it. Number of symbol corresponds to the study ID number.