Use of sequence-based typing for investigation of a case of nosocomial legionellosis

Isolation of Legionella pneumophila by Co-culture with Local Ameba, Canada

Legionellosis was diagnosed in an immunocompromised 3-year-old girl in Canada. We traced the source of the bacterium through co-culture with an ameba collected from a hot tub in her home. We identified Legionella pneumophila serogroup 6, sequence type 185, and used whole-genome sequencing to confirm the environmental and clinical isolates were of common origin.

Occurrence and distribution of sequence types among Legionella pneumophila strains isolated from patients in Germany: common features and differences to other regions of the world

A total of 105 unrelated clinical isolates of Legionella pneumophila were randomly selected from the German National Legionella strain collection and typed by monoclonal antibody (MAb) subgrouping and a seven-gene locus sequence-based typing (SBT) scheme. According to the case definitions of the European Working Group for Legionella Infections, 19 of the isolates tested were travel-associated, 38 were community-acquired and 48 were of nosocomial origin. Eighty-four of these strains belonged to serogroup 1, 20 belonged to other serogroups, and one isolate could not be serogrouped. The majority of strains among the travel-associated and community-acquired cases were MAb3-1-positive. The most common sequence type (1, 4, 3, 1, 1, 1, 1) was found in 20 isolates in 11 cities; other allelic profiles also found in Europe (2, 3, 9, 10, 2, 1, 6), (1, 3, 9, 10, 2, 1, 6), (2, 6, 17, 14, 13, 11, 11) and (3, 4, 1, 1, 1, 9, 1) were detected among the German isolates but at a low frequency. In contrast, some SBT are unique to Germany, including (3, 4, 1, 3, 35, 9, 11), which was found among five isolates from patients in Berlin. In concordance with European data, a significant portion of the L. pneumophila strains isolated from patients in Germany belong to clones that occur throughout the world and which are responsible for the majority of clinical cases.

External quality assessment of a DNA sequence-based scheme for epidemiological typing of Legionella pneumophila by an international network of laboratories

We report the results of an international external quality assessment (EQA) program to assess the performance of laboratories in genotyping Legionella pneumophila isolates using the standard European Working Group for Legionella Infections sequence-based typing protocol. Three coded distributions of L. pneumophila isolates were sent to laboratories in 12, 14, and 20 countries, respectively. The data were returned by 11 of 16, 18 of 19, and 27 of 29 centers, respectively. Incomplete submission of data resulted in exclusion from certain aspects of the analyses. The number of centers achieving 100% score, for all loci tested, rose successively from 50% (5 of 10) for the first EQA distribution, to 56% (9 of 16) for the second EQA distribution, to 76% (19 of 25) for the third EQA distribution. A number of additional centers made only a few errors (one to three) in each distribution. Sequence data from the first two distributions were collected in flat text file format and using specially developed software, the sequence quality tool (SQT), in the third distribution. The SQT allows users to upload trace files in standard file formats, automates basecalling using phred and phrap software, contig assembly, trimming, and matching against a reference library. The program described here allow users an independent measure of sequence quality, and such schemes are vital in order to identify strengths and weakness in centers responsible for the generation of genotyping data in legionella outbreak investigation. The present study demonstrates that DNA sequence data can be highly reproducible but, when independently assessed, in practice frequently falls short of this goal. However, experience and training in the methodology results in increased performance.