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Genomic Analysis Sheds Light on Legionnaires' Disease Outbreaks

A genetic analysis of Legionella pneumophila — the freshwater bacteria that is the primary cause of Legionnaires' disease — covering samples from more than three decades is presented in The Lancet Microbe this week, highlighting the benefits of genomic surveillance to address outbreaks of the pneumonic illness. Although most Legionnaires' disease cases are sporadic and unrelated to other infections, outbreaks can occur when a cluster of infections are linked to a common source such as air-conditioning systems. Despite an increase in the frequency of Legionnaires' disease infection, the epidemiology of infections remains unclear. In this week's study, a team led by scientists from the University of Edinburgh compared the genome sequences for all clinical isolates of L. pneumophila in Scotland between 1984 and 2020 with a sequence dataset of 3,211 local and globally representative isolates. They find that many Scottish Legionnaires' disease infections are caused by a small number of widely disseminated and previously undetected L. pneumophila clones found in community-, travel-, and hospital-related environments. "In light of these findings, we propose that cluster and outbreak definitions should be reconsidered and propose [whole-genome sequencing]-based surveillance as a critical public health tool for real-time identification and mitigation of clinically important endemic clones," the study's authors write