Abstract
During the water crisis in Flint, Michigan, USA (2014–2015), 2 outbreaks of Legionnaires’ disease occurred in Genesee County, Michigan. We compared whole-genome sequences of 10 clinical Legionella pneumophila isolates submitted to a laboratory in Genesee County during the second outbreak with 103 water isolates collected the following year. We documented a genetically diverse range of L. pneumophila strains across clinical and water isolates. Isolates belonging to 1 clade (3 clinical isolates, 3 water isolates from a Flint hospital, 1 water isolate from a Flint residence, and the reference Paris strain) had a high degree of similarity (2–1,062 single-nucleotide polymorphisms), all L. pneumophila sequence type 1, serogroup 1. Serogroup 6 isolates belonging to sequence type 2518 were widespread in Flint hospital water samples but bore no resemblance to available clinical isolates. L. pneumophila strains in Flint tap water after the outbreaks were diverse and similar to some disease-causing strains.
Highlights
During the water crisis in Flint, Michigan, USA (2014–2015), 2 outbreaks of Legionnaires’ disease occurred in Genesee County, Michigan
Our study objective was to use next-generation DNA sequencing to compare L. pneumophila isolated from Flint tap water after the second Legionnaires’ disease outbreak with tap water isolates from neighboring drinking water systems outside of Flint that were never served by Flint River water and clinical strains received during the second outbreak at a regional reference laboratory in Genesee County
22 (58%) of 38 hospital samples from March 2016, eight (2%) of 370 residence samples from June 2016, and 6 (21%) of 28 residence samples from August 2016 were positive for culturable L. pneumophila
Summary
During the water crisis in Flint, Michigan, USA (2014–2015), 2 outbreaks of Legionnaires’ disease occurred in Genesee County, Michigan. We compared whole-genome sequences of 10 clinical Legionella pneumophila isolates submitted to a laboratory in Genesee County during the second outbreak with 103 water isolates collected the following year. Isolates belonging to 1 clade (3 clinical isolates, 3 water isolates from a Flint hospital, 1 water isolate from a Flint residence, and the reference Paris strain) had a high degree of similarity (2–1,062 single-nucleotide polymorphisms), all L. pneumophila sequence type 1, serogroup 1. Our study objective was to use next-generation DNA sequencing to compare L. pneumophila isolated from Flint tap water after the second Legionnaires’ disease outbreak with tap water isolates from neighboring drinking water systems outside of Flint that were never served by Flint River water and clinical strains received during the second outbreak at a regional reference laboratory in Genesee County. In addition to serogroup testing, we used whole-genome sequencing to compare isolates in terms of sequence type (ST), average nucleotide identity, and single-nucleotide polymorphisms (SNPs)
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