title: Risk factors for gastroenteritis associated with canal swimming in two cities in the Netherlands during the summer of 2015: A prospective study.
abstract: Urban canal swimming events are popular in the Netherlands. In 2015, two city canal swimming events took place, in Utrecht (Utrecht Singel Swim, USS) and in Amsterdam (Amsterdam City Swim, ACS). This prospective study characterizes the health risks associated with swimming in urban waters. Online questionnaires were sent to 160 (USS) and 2,692 (ACS) participants, with relatives of participants who did not swim completing the questionnaire as a control. Swimming water specimens and stool specimens of diarrheic participants in the ACS group were analysed. A total of 49% of USS and 51% of ACS swimmers returned their questionnaires. Nine percent of USS swimmers and 4% of non-swimmers reported gastrointestinal complaints (aRR 2.1; 95% CI: 0.3-16), while a total of 31% of ACS swimmers and 5% of non-swimmers reported gastrointestinal complaints (aRR 6.3; 95% CI: 4.1-9.5). AGI risk among ACS participants was directly related to increasing number of mouthfuls of water swallowed. Various norovirus genotypes were detected in five out of seven stool specimens taken from ACS participants and in all three tested ACS water samples. We conclude that the AGI risk among open-water swimmers in urban areas depends on the circumstances around the event. The epidemiological curve, the statistical association between swimming and AGI, and the microbiological evidence for norovirus in stool and water specimens suggest that AGI outbreak after the ACS event was due to water contamination by multiple norovirus strains, which is possibly linked to sewage overflow due to prior heavy rainfall. There is need for more targeted preventive measurements and recommendations for organizers, municipal authorities and participants to prevent this reoccurring in the future.
authors.affiliation: Public Health Service Utrecht Region, Zeist, the Netherlands.
authors.forename: Rosa
authors.identifier: http://orcid.org/0000-0002-9067-4951
authors.initials: R
authors.lastname: Joosten
authors.affiliation: Public Health Service Amsterdam, Amsterdam, the Netherlands.|Division of Infectious Diseases, Department of Internal Medicine, Academic Medical Center (AMC), University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Gerard
authors.initials: G
authors.lastname: Sonder
authors.affiliation: Centre for Infectious Diseases, Epidemiology and Surveillance, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.|European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden.
authors.forename: Saara
authors.initials: S
authors.lastname: Parkkali
authors.affiliation: Public Health Service Utrecht Region, Zeist, the Netherlands.
authors.forename: Diederik
authors.initials: D
authors.lastname: Brandwagt
authors.affiliation: Public Health Service Utrecht Region, Zeist, the Netherlands.|Centre for Infectious Diseases, Epidemiology and Surveillance, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Ewout
authors.initials: E
authors.lastname: Fanoy
authors.affiliation: Centre for Infectious Diseases, Epidemiology and Surveillance, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Lapo
authors.initials: L
authors.lastname: Mughini-Gras
authors.affiliation: Centre for Infectious Diseases, Epidemiology and Surveillance, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Willemijn
authors.initials: W
authors.lastname: Lodder
authors.affiliation: Public Health Service Utrecht Region, Zeist, the Netherlands.
authors.forename: Erik
authors.initials: E
authors.lastname: Ruland
authors.affiliation: Public Health Service Amsterdam, Amsterdam, the Netherlands.
authors.forename: Evelien
authors.initials: E
authors.lastname: Siedenburg
authors.affiliation: Public Health Service Amsterdam, Amsterdam, the Netherlands.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Kliffen
authors.affiliation: Centre for Infectious Diseases, Epidemiology and Surveillance, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Wilfrid
authors.initials: W
authors.lastname: van Pelt
mesh_terms: D000293:Adolescent; D000328:Adult; D017250:Caliciviridae Infections / Q000453:epidemiology* / Q000821:virology; D004196:Disease Outbreaks / Q000517:prevention & control / Q000706:statistics & numerical data; D004755:Enterobacteriaceae / Q000302:isolation & purification*; D004756:Enterobacteriaceae Infections / Q000453:epidemiology* / Q000382:microbiology; D005243:Feces / Q000382:microbiology; D005260:Female; D005618:Fresh Water / Q000382:microbiology / Q000821:virology; D005759:Gastroenteritis / Q000453:epidemiology* / Q000382:microbiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D029322:Norovirus / Q000302:isolation & purification*; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013550:Swimming; D014871:Water Microbiology; D014876:Water Pollution / Q000009:adverse effects; D060753:Water Quality; D055815:Young Adult