A waterborne outbreak with a single clone of Campylobacter jejuni in the Danish town of Køge in May 2010

Abstract

Background: In Denmark, large-scale waterborne outbreaks are rare. This report describes the investigation of an outbreak that occurred in the town of Køge in May 2010. Methods: The epidemiological investigation consisted of hypothesis generating telephone interviews, followed by a cohort study among approximately 20,000 residents using an online questionnaire. Odds ratios were calculated for exposures including the number of glasses of tap water consumed. Geographical spreading was assessed using a geographical information system. The microbiological investigation included cultures of stool samples and flagellin-typing. In the environmental investigation, water samples were tested for Escherichia coli and coliform counts and for DNA of Campylobacter, Enterococcus, and Bacteroides. During the outbreak investigation a water boiling order was enforced, as tap water was considered a potential source. Results: Of 45 patients with laboratory confirmed Campylobacter infection in the municipality of Køge in May, 43 lived in the area covered by the central water supply. Of 61 patients with laboratory confirmed Campylobacter jejuni by 8 June, 50 shared a common flagellin gene type – flaA type 36 (82%). The epidemic curve from the cohort study showed a wave of diarrhoea onset from 14 to 20 May (n = 176). Among these patients, the development of diarrhoea was associated with drinking tap water with a dose–response pattern (linear increase by 2 glasses: odds ratio 1.40, 95% confidence interval 1.16–1.70). No bacterial DNA was found in water samples. Conclusions: These findings indicated a point source contamination of tap water with a single clone of C. jejuni which likely occurred on 12–13 May. The water boiling order was lifted on 18 June.

Keywords::

• Outbreak
• waterborne
• Campylobacter jejuni

Acknowledgements

We would like to thank all residents of Køge, who provided us with information through the questionnaire. We also thank the members of the outbreak investigation team for the good collaboration, in particular Bjarne Bringedal Svendsen, Tove Frederiksen, Charlotte Sten Jacobsen, Peter Tuxen, Merete Olsen and Birte Hvarregaard (Køge Municipality, Denmark), Morten Lisby and Susanne Olsen (Danish Veterinary and Food Administration, Denmark), Boye Rasmussen (Police, Denmark) and Carl-Johan Viereck (Preparedness Køge Municipality, Denmark). Special thanks also to Eva Møller Nielsen (Department of Microbiological Surveillance and Research, Statens Serum Institut, Copenhagen, Denmark) for her assistance in the microbiological investigation, and Marion Muehlen (European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control, Stockholm, Sweden) for her feedback on the manuscript.

Declaration of interest: The authors declare that they have no competing interests. The outbreak investigation was financed by the collaborating partners, being Køge Municipality, Køge Vand A/S, the public health medical officers of Zealand, and Statens Serum Institut.