A case of Legionnaires' disease linked to the household hot water system, confirmed by whole genome sequencing.

Legionella pneumophila - an opportunistic bacterial pathogen frequently identified in the environmental water samples - can produce human infections after inhalation of contaminated aerosols. We describe a case of Legionnaires' disease linked to a household drinking water system. Serogroup 1 L. pneumophila isolates were recovered from both human and environmental samples and were analysed by whole genome sequencing (WGS). Phylogenetic relatedness inferred by core genome multi-locus sequence typing (cgMLST) revealed the household drinking water system as the source of isolates causing human infection. This epidemiological investigation performed in Romania and identifying the source of infection by WGS is the first of this kind for our country. The human and environmental isolates were undoubtedly linked through the use of high-discriminatory WGS analysis, which confirmed the relatedness inferred from the classical seven-loci sequence-based typing (SBT) scheme.