Sero-epidemiology of legionellosis in Austria

Out of 1961 patients with the clinical diagnosis of atypical pneumonia 11 cases (0.65%) of recent Legionella infections were diagnosed by indirect immunofluorescence test (IFA). A higher incidence (1.37%) has been found in 364 patients in whom clinicians suspected a Legionella infection and therefore asked for serological testing. Prevalence of antibodies (greater than or equal to 1:32) reacting with antigens of L. pneumophila serogroup 1 to 6 was highest to serogroup 6 (37%), and lowest to serogroup 1 (4.3%). Specificity of IFA for reciprocal titer of 128 to L. pneumophila serogroup 1 was calculated with 99.5%, for serogroup 6 with only 87.7%. Morbidity of severe Legionella pneumonias in Austria can be estimated at about 1.5 cases per 100 000 inhabitants.