Exposure to Legionella in geriatric institutions.

A study of seroreactivity to six Legionella species (L. pneumophila, L. longbeachae, L. micdadei, L. gormanii, L. dumoffii and L. bozemanii) performed in two geriatric hospitals, a day club for the aged and a group of aged with independent life styles revealed a high prevalence of seropositivity in the hospitals. A titer of 1:256 to at least one antigen was obtained in 30.5% of the patients and 35.7% of the staff members from one hospital, 12.1% of the patients and 17.2% of the staff members from a second hospital, 9.1% of the day club attendants, and in none of the 26 old people living in their own households. A second study of the possible source of Legionella spp. in three geriatric hospitals was performed. Three strains of L. pneumophila [serogroup (SG) 1, 3 and 6] were isolated from water, one water sample was positive for L. pneumophila SG 1-4 (pool), by direct immunofluorescence staining only. In a survey of seroconversion to Legionella antigens, 105 new patients were investigated on their arrival day and over a 2-year period; 24% of the patients who could be followed up significantly seroconverted to at least one of the Legionella antigens. Although the findings proved that Legionella existed on the premises of two hospitals, and the high prevalence of seropositivity to Legionella spp. indicated intramural exposure to the agents of legionellosis at one hospital, we found no evidence linking these agents to patient illness.