A large outbreak of gastrointestinal illness at an open-water swimming event in the River Thames, London. Issue 6 (6th February 2017)

• Record Type: Journal Article
• Authors: HALL, V.; TAYE, A.; WALSH, B.; MAGUIRE, H.; DAVE, J.; WRIGHT, A.; ANDERSON, C.; CROOK, P.
• Is Part Of: Epidemiology and infection. Volume 145:Issue 6(2017)
• Page Start: 1246
• Page End: 1255
• Publication Date: 2017-02-06
• Subjects: Community epidemics, -- gastrointestinal infections, -- water (quality), -- waterborne infections; Communicable diseases -- Periodicals; Epidemiology -- Periodicals; 614.4
• DOI: 10.1017/S0950268816003393
• Languages: English
• ISSNs: 0950-2688

Abstract

SUMMARY: Open-water swimming is increasingly popular, often in water not considered safe for bathing. Limited evidence exists on the associated health risks. We investigated gastrointestinal illness in 1100 swimmers in a River Thames event in London, UK, to describe the outbreak and identify risk factors. We conducted a retrospective cohort study. Our case definition was swimmers with any: diarrhoea, vomiting, abdominal cramps lasting ⩾48 h, nausea lasting ⩾48 h, with onset within 9 days after the event. We used an online survey to collect information on symptoms, demographics, pre- and post-swim behaviours and open-water experience. We tested associations using robust Poisson regression. We followed up case microbiological results. Survey response was 61%, and attack rate 53% (338 cases). Median incubation period was 34 h and median symptom duration 4 days. Five cases had confirmed microbiological diagnoses (four Giardia, one Cryptosporidium ). Wearing a wetsuit [adjusted relative risk (aRR) 6·96, 95% confidence interval (CI) 1·04–46·72] and swallowing water (aRR 1·42, 95% CI 1·03–1·97) were risk factors. Recent river-swimming (aRR 0·78, 95% CI 0·67–0·92) and age >40 years (aRR 0·83, 95% CI 0·70–0·98) were protective. Action to reduce risk of illness in future events is recommended, including clarification of oversight arrangements for future swims to ensure appropriate risk assessment and advice is provided.