Abstract
An outbreak of Legionnaires’ disease affected 18 people in Montpellier, a town of the south of France, between December 2016 and July 2017. All cases were diagnosed by a positive urinary antigen test. No deaths were reported. Epidemiological, environmental and genomic investigations (nested Sequence-Based Typing (nSBT) and whole genome sequencing) were undertaken. For the cases for which we had information, four had a new isolate (ST2471), one had a different new isolate (ST2470), one had a genomic pattern compatible with the ST2471 identified by nSBT (flaA = 3), and one had a genomic pattern not compatible with two previous identified STs (pilE = 6). The analysis conducted on the pool of an aquatic therapy center revealed seven isolates of Legionella pneumophila. Whole genome analysis confirmed the link between the environmental and clinical isolates for both ST2470 and ST2471. As the outbreak occurred slowly, with several weeks between new cases, it was not possible to immediately identify a common source. The sixth case was the first to report having aquatic therapy care. Of the 18 cases, eight had attended the aquatic therapy center and the other 10 were inhabitants who lived, worked or walked close to the center. The main cause for this outbreak was the lack of facility maintenance. This investigation highlights the risk to public health of aquatic therapy centers for users and nearby populations, and emphasizes the need for risk reduction measures with specific guidelines to improve health and safety in aquatic facilities.
Highlights
Legionnaires’ disease (LD) is a form of pneumonia caused by Legionella, a bacterium mostly present in man-made water systems
A new strain (ST2470) was isolated from a patient who had received physiotherapy care in the aquatic therapy centre (ATC), while a different new strain (ST2471) was isolated for two patients who had received aquatic therapy care, another who lived in the district, and one case who frequented the district but did not live there (Table 1)
Difficulties in identifying the source and strains required actors to refocus investigations, which led to an extended response time before controlling the outbreak
Summary
Legionnaires’ disease (LD) is a form of pneumonia caused by Legionella, a bacterium mostly present in man-made water systems. It is usually acquired by inhalation of contaminated aerosols [1,2]. For most of LD cases, the source of contamination cannot be definitively identified [3]. Control of LD outbreaks relies on descriptive epidemiological data, combined with microbiological information to identify the source and implement control measures. In France, LD is mandatorily notifiable [4]; 1 218 LD cases were notified in 2016, with an annual notification rate of 1.8/100,000 inhabitants. Twenty-two percent of notified cases in 2016 had clinical isolates typed by the National Reference Centre for Legionella (NRC-L)
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