Molecular characterization of clinical and environmental isolates of Legionella pneumophila in Norway, 2001–2008

Abstract

Background: The aims of the study were to determine the molecular characteristics of a collection of Legionella pneumophila isolates from 45 cases with Legionnaires’ disease and from 96 environmental samples, received by the national reference laboratory in Norway between 2001 and 2008, to use these characteristics to identify links between cases and suspected sources of infection, and to compare the isolate characteristics with those in other European countries. Methods: The isolates were characterized by 7-gene locus sequence-based typing and dot-blotting with monoclonal antibodies to various serogroups and subgroups. Results: The clinical isolates represented 12.6% of the 357 cases notified in Norway between 2001 and 2008, during which 3 outbreaks of L. pneumophila serogroup 1 occurred. Outbreak cases constituted 62.2% of the cases, followed by travel-associated (24.4%) and sporadic cases (11.1%). Forty-two (93.3%) of the clinical and 69 (71.9%) of the environmental isolates were serogroup 1, and 39 (86.7%) and 50 (52.1%) isolates, respectively, carried the monoclonal antibody (Mab) 3/1 virulence-associated epitope. The clinical isolates belonged to 17 sequence types and the environmental isolates to 19 sequence types. neuA was not detected in 23 environmental isolates. Conclusions: Matching characteristics of sequence types and monoclonal subgroups for case and environmental isolates were obtained for all 3 outbreaks and for 2 of 5 cases of sporadic disease. Sampling during the outbreaks accounted for the higher proportion of serogroup 1 and Mab 3/1-positive environmental isolates in comparison with other European strain collections.

Keywords::

• Legionella pneumophila
• multilocus sequence typing
• monoclonal antibodies

Acknowledgements

We are grateful to the national laboratories for supplying the isolates and to Anne Ramstad Alme and Gunnhild Rødal, NIPH, for isolation and agglutination of the isolates.

Declaration of interest: This study was funded by the Norwegian Institute of Public Health. The authors have no conflict of interest.