Chapter 36 : Legionella Serogroup and Subgroup Distribution among Patients with Legionnaires' Disease in Denmark

Abstract:

From January 1994 to June 2000, legionellae were isolated by culture from 195 patients with Legionnaires’ disease in Denmark. In this survey the authors present the Legionella serogroup and Legionella subgroup distribution of the isolates stratified according to where the patients acquired the infection: in the community (in Denmark) or during hospitalization or during traveling abroad. Isolates from 190 patients were L. pneumophila of which 185 could be assigned to a definitive serogroup or subgroup. Five isolates were non-L. pneumophila: one was L. micdadei, two were L. hozemanii, and two were L. longbeachae. For cases where the infection was acquired in Denmark, only 39.7% (69 of 174) of cases were caused by L. pneumophila serogroup 1 (Pontiac subgroups only 27.6%). L. pneumophila serogroup 3 was a relatively common cause of community-acquired and nosocomial Legionnaires’ disease in Denmark, accounting for 20% of all culture-confirmed cases. The sensitivities of the commercially available Legionella urinary antigen tests for serogroups other than serogroup 1 is low and is also lower for serogroup 1 non-Pontiac subgroups than for Pontiac subgroups. It is therefore important to supplement the use of Legionella urinary antigen assays in the diagnosis of Legionnaires' disease with other methods such as PCR and culture, particularly for the groups of patients with underlying disease and for those who are infected during hospitalization.