Febrile illness in successive cohorts of tourists at a hotel on the Italian Adriatic coast: evidence for a persistent focus of Legionella infection.

Outbreaks of febrile illness consistent with legionellosis occurred in successive groups of vacationers at an Adriatic resort in 1980. Illness was associated with one of two hotels used by the groups. A cohort study of guests of the suspect hotel revealed 23 cases of febrile illness with pulmonary symptoms, significant antibody titers to Legionella pneumophila, or both, among 291 persons at risk. Two patients died. Attack rates ranged from 0-19% in the nine cohorts of vacationers and were highest among the most elderly. Febrile illness in the last two cohorts of the season was associated with an antibody titer greater than or equal to 128. L. pneumophila was isolated from shower heads in the suspect hotel, but no association was found between showering and illness or seropositivity. Bacteria identified as L. pneumophila by direct immunofluorescence were also found in water from an adjacent hotel and from the outflow from a common well. No cases were associated with the adjacent hotel.