Epidemiological patterns in legionellosis in Sweden

Since 1976, 173 confirmed cases of legionellosis of the pneumonic type have been reported in Sweden. Sixty-eight cases belonged to a community-acquired outbreak in the summer and fall of 1979. Fourty percent of the sporadic cases are travel-associated. Half of them had visited Mediterranean countries. As much as 76% of the sporadic cases were men, 23% men of the age groups 15--54 years. There is an ongoing nosocomial outbreak in a renal transplant unit. L. pneumophila belonging to serogroups 1, 3, 5 and 6 have been isolated from patients or environment (e.g. from the cooling tower of a shopping mall in connection with the community-acquired outbreak and tap water in the nosocomial outbreak). A few cases of L. micdadei and L. bozemanii infections have been diagnosed. The proportion of legionellosis among all community-acquired pneumonia patients in a prospective study was only 1.8%. The frequency of antibodies to L. pneumophila among blood donors in non-endemic areas ranged between 0--6% compared to 20--21% in areas where outbreaks have occurred. The fatality rate has been low and the clinical outcome satisfactory even in cases without adequate antibiotic treatment.