title: Public Health Investigation of Two Outbreaks of Shiga Toxin-Producing Escherichia coli O157 Associated with Consumption of Watercress.
abstract: An increase in the number of cases of Shiga toxin-producing Escherichia coli (STEC) O157 phage type 2 (PT2) in England in September 2013 was epidemiologically linked to watercress consumption. Whole-genome sequencing (WGS) identified a phylogenetically related cluster of 22 cases (outbreak 1). The isolates comprising this cluster were not closely related to any other United Kingdom strain in the Public Health England WGS database, suggesting a possible imported source. A second outbreak of STEC O157 PT2 (outbreak 2) was identified epidemiologically following the detection of outbreak 1. Isolates associated with outbreak 2 were phylogenetically distinct from those in outbreak 1. Epidemiologically unrelated isolates on the same branch as the outbreak 2 cluster included those from human cases in England with domestically acquired infection and United Kingdom domestic cattle. Environmental sampling using PCR resulted in the isolation of STEC O157 PT2 from irrigation water at one implicated watercress farm, and WGS showed this isolate belonged to the same phylogenetic cluster as outbreak 2 isolates. Cattle were in close proximity to the watercress bed and were potentially the source of the second outbreak. Transfer of STEC from the field to the watercress bed may have occurred through wildlife entering the watercress farm or via runoff water. During this complex outbreak investigation, epidemiological studies, comprehensive testing of environmental samples, and the use of novel molecular methods proved invaluable in demonstrating that two simultaneous outbreaks of STEC O157 PT2 were both linked to the consumption of watercress but were associated with different sources of contamination.
authors.affiliation: Gastrointestinal Bacteria Reference Unit, Public Health England, Colindale, London, United Kingdom claire.jenkins@phe.gov.uk.
authors.forename: Claire
authors.initials: C
authors.lastname: Jenkins
authors.affiliation: Gastrointestinal Bacteria Reference Unit, Public Health England, Colindale, London, United Kingdom.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Dallman
authors.affiliation: Gastrointestinal and Emerging Zoonotic Infections Department, Public Health England, Colindale, London, United Kingdom.
authors.forename: Naomi
authors.initials: N
authors.lastname: Launders
authors.affiliation: Food, Water, and Environmental Microbiology Laboratory Porton, Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Caroline
authors.initials: C
authors.lastname: Willis
authors.affiliation: Gastrointestinal and Emerging Zoonotic Infections Department, Public Health England, Colindale, London, United Kingdom.
authors.forename: Lisa
authors.initials: L
authors.lastname: Byrne
authors.affiliation: Food, Water, and Environmental Microbiology Laboratory Porton, Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Frieda
authors.initials: F
authors.lastname: Jorgensen
authors.affiliation: Department of Biology, The University of Texas at San Antonio, San Antonio, Texas, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Eppinger
authors.affiliation: Gastrointestinal and Emerging Zoonotic Infections Department, Public Health England, Colindale, London, United Kingdom.
authors.forename: Goutam K
authors.initials: GK
authors.lastname: Adak
authors.affiliation: Food, Water, and Environmental Microbiology Laboratory York, Public Health England, York, United Kingdom.
authors.forename: Heather
authors.initials: H
authors.lastname: Aird
authors.affiliation: Food, Water, and Environmental Microbiology Laboratory London, Public Health England, Colindale, London, United Kingdom.
authors.forename: Nicola
authors.initials: N
authors.lastname: Elviss
authors.affiliation: Gastrointestinal Bacteria Reference Unit, Public Health England, Colindale, London, United Kingdom.
authors.forename: Kathie A
authors.initials: KA
authors.lastname: Grant
authors.affiliation: Gastrointestinal and Emerging Zoonotic Infections Department, Public Health England, Colindale, London, United Kingdom.
authors.forename: Dilys
authors.initials: D
authors.lastname: Morgan
authors.affiliation: Food, Water, and Environmental Microbiology Laboratory London, Public Health England, Colindale, London, United Kingdom.
authors.forename: Jim
authors.initials: J
authors.lastname: McLauchlin
mesh_terms: D000818:Animals; D000829:Animals, Domestic; D002417:Cattle; D004196:Disease Outbreaks / Q000517:prevention & control; D004927:Escherichia coli Infections / Q000453:epidemiology* / Q000382:microbiology* / Q000517:prevention & control; D005516:Food Microbiology; D016680:Genome, Bacterial; D006801:Humans; D031223:Nasturtium / Q000382:microbiology*; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D054323:Shiga-Toxigenic Escherichia coli / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D006113:United Kingdom / Q000453:epidemiology
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