The prevalence of seropositivity to Legionella spp. was studied in inmates and staff members of two geriatric hospitals (Rahel and Sinai); attendants to a geriatric Day Club; and 26 old people with entirely independent households. The sera were examined by indirect immunofluorescence with antigens of six Legionella species (L. pneumophila, L. longbeachae, L. micdadei, L. gormanii, L. dumoffii and L. bozemanii). A titre of greater than or equal to 256 to at least one antigen was obtained in 30.5% of patients and 35.7% of staff members from Rahel; 12.1% of patients and 17.2% of staff members from Sinai; 9.1% of attendants to the Day Club; and none of 26 old people with their own households. All the positive patients from Rahel reacted with L. pneumophila, but only four of seven of the positive patients from Sinai did so; none of the seropositive subjects from the Day Club reacted with this agent. The results indicate intramural exposure to agents of legionellosis, at least for the Rahel Hospital.
