Variable genetic element typing: a quick method for epidemiological subtyping of Legionella pneumophila

Rapid genotyping of Legionella pneumophila serogroup 1 strains by a novel DNA microarray-based assay during the outbreak investigation in Warstein, Germany 2013

Between 1 August and 6 September 2013, an outbreak of Legionnaires' disease (LD) with 78 cases confirmed by positive urinary antigen tests occurred in Warstein, North Rhine-Westphalia, Germany. Legionella (L.) pneumophila, serogroup (Sg) 1, monoclonal antibody (mAb) subgroup Knoxville, sequence type (ST) 345, was identified as the epidemic strain. This strain was isolated from seven patients. To detect the source of the infection, epidemiological typing of clinical and environmental strains was performed in two consecutive steps. First, strains were typed by monoclonal antibodies. Indistinguishable strains were further subtyped by sequence-based typing (SBT) which is the internationally recognized standard method for epidemiological genotyping of L. pneumophila. In an early stage of the outbreak investigation, many environmental isolates were found to belong to the mAb subgroup Knoxville, but to two different STs, namely to ST 345, the epidemic strain, and to ST 600. A majority of environmental isolates belonged to ST 600 whereas the epidemic ST 345 strain was less common in environmental samples. To rapidly distinguish both Knoxville strains, we applied a novel typing method based on DNA-hybridization on glass chips. The new assay can easily and rapidly discriminate L. pneumophila Sg 1 strains. Thus, we were able to quickly identify the sources harboring the epidemic strain, i.e., two cooling towers of different companies, the waste water treatment plants (WWTP) of the city and one company as well as water samples of the river Wester and its branches.

Real-time investigation of a Legionella pneumophila outbreak using whole genome sequencing

Legionella pneumophila is the main pathogen responsible for outbreaks of Legionnaires' disease, which can be related to contaminated water supplies such as cooling towers or water pipes. We combined conventional molecular methods and whole genome sequence (WGS) analysis to investigate an outbreak of L. pneumophila in a large Australian hospital. Typing of these isolates using sequence-based typing and virulence gene profiling, was unable to discriminate between outbreak and non-outbreak isolates. WGS analysis was performed on isolates during the outbreak, as well as on unlinked isolates from the Public Health Microbiology reference collection. The more powerful resolution provided by analysis of whole genome sequences allowed outbreak isolates to be distinguished from isolates that were temporally and spatially unassociated with the outbreak, demonstrating that this technology can be used in real-time to investigate L. pneumophila outbreaks.