RESEARCH Vero Cytotoxin–Producing Escherichia coli O157 Gastroenteritis in Far m Visitors, Nor th Wales Christopher J.I. Payne,* Marko Petrovic,† Richard J. Roberts,† Ashish Paul,† Eithne Linnane,† Mark Walker,‡ David Kirby,§ Anthony Burgess,¶ Robert M.M. Smith,* Thomas Cheasty,# Geraldine Willshaw,# and Roland L. Salmon*1 An outbreak of Vero cytotoxin–producing Escherichia coli O157 (VTEC O157) gastroenteritis in visitors to an open farm in North Wales resulted in 17 primary and 7 sec- ondary cases of illness. E. coli O157 Vero cytotoxin type 2, phage type 2 was isolated from 23 human cases and envi- ronmental animal fecal samples. A case-control study of 16 primary case-patients and 36 controls (all children) showed a significant association with attendance on the 2nd day of a festival, eating ice cream or cotton candy (candy floss), and contact with cows or goats. On multivariable analysis, only the association between illness and ice cream (odds ratio [OR]=11.99, 95% confidence interval [CI] 1.04 to 137.76) and cotton candy (OR=51.90, 95% CI 2.77 to 970.67) remained significant. In addition to supervised handwashing, we recommend that foods on open farms only be eaten in dedicated clean areas and that sticky foods be discouraged. Hstrains of Escherichia coli O157 (VTEC O157) can uman illness caused by Vero cytotoxin–producing occur after direct contact with farm animals. Although the annual rate of VTEC O157–reported illness in the general population in England and Wales is relatively low, ranging from 1.28 to 2.10 /100,000/year from 1995 to 1998 (1), young children who become ill are at particular risk for serious complications, such as hemolytic uremic syn- drome. An estimated half million to 10 million visits each year are made to approximately 1,000 open farms (i.e., a work- ing farm that allows visitors, usually for an entry fee) in England and Wales (2; Association of Farms for Schools, pers. comm.). However, only occasional outbreaks of VTEC O157 associated with such visits are reported: eight *Communicable Disease Surveillance Centre (Wales), Cardiff, Wales; †Department of Public Health, North Wales Health Authority, Mold, Wales; ‡Public Health Laboratory, Bangor, Wales; §Veterinary Laboratory Agency, Aberystwyth, Wales; ¶Isle of Anglesey County Council, Anglesey, Wales; and #Public Health Laboratory Service Central Public Health Laboratory, London, UK outbreaks of VTEC O157 in visitors to open farms in England and Wales were reported to the Laboratory for Enteric Pathogens at Colindale in 1992 through 2000 (3–7). The largest outbreak in the United Kingdom during this period consisted of seven cases (5). Individual cases associated with open farms are rarely reported (8). Of 71 reported cases of E. coli O157 in Wales during 1998, two primary case-patients reported visiting an open farm in the previous week (Communicable Disease Surveillance Centre, Wales, unpub. data). Recognition of the risk of acquiring zoonotic infection, particularly gastrointestinal illness, has led to written guidelines for open farms (9). The guidelines concentrate on farm layout, clear routes for visitors to follow, staff training, control of animal contact, separate eating areas, adequate handwashing facilities, and adequate information in the form of notices or leaflets. These recommendations are derived from an understanding of how pathogens are likely to be spread to humans. However, the popularity of farms as a tourist attraction, when compared with the infre- quency of illness, suggests that quite specific risks may occasionally occur. The opportunities for studying these risk factors more systematically are limited, as outbreaks are so infrequent. A large outbreak of gastroenteritis in North Wales, associated with VTEC O157, presented an opportunity to conduct a case-control study to investigate 1C. Payne designed the case-control study, drew up the question- naire, and analyzed and wrote up the results. M. Petrovic helped design the questionnaire, organized the data collection, and wrote the sections describing the outbreak and microbiologic findings. R.J. Roberts contributed toward the study and questionnaire design, including devising the method of selecting controls; he also helped in the final drafts of the paper. R.L. Salmon originally conceived the study, commented on the questionnaire design, and helped interpret the findings. T. Cheasty was responsible for con- firmation and typing of isolates. G. Willshaw performed DNA- based comparison of strains. Other authors made important con- tributions to the investigation and control of the outbreak and par- ticipated in writing the paper. 526 Emerging Infectious Diseases • Vol. 9, No. 5, May 2003