Outbreaks of Escherichia coli O157:H7 Infections Among Children Associated With Farm Visits --- Pennsylvania and Washington, 2000

During the spring and fall of 2000, outbreaks of Escherichia coli O157:H7 infections among school children in Pennsylvania and Washington resulted in 56 illnesses and 19 hospitalizations. Illness was associated with school and family visits to farms where children came into direct contact with farm animals. This report summarizes the findings of investigations of these outbreaks (Figure 1) and includes strategies to reduce the transmission of enteric pathogens from farm animals to children.

Pennsylvania

During September--November 2000, the Montgomery County Health Department (MCHD) identified 51 persons who had diarrhea within 10 days of visiting a dairy farm (farm A) in Montgomery County. Fifteen (29%) persons had either E. coli O157 isolated from stool specimens or hemolytic-uremic syndrome (HUS); patients ranged in age from 1--52 years (median: 4 years), 26 (51%) were male, and dates of illness onset ranged from September 4 to November 8. Symptoms reported by the 51 patients included bloody diarrhea (37%), fever (45%), and vomiting (45%); 16 (31%) patients were hospitalized and eight (16%) developed HUS. E. coli O157 isolates were indistinguishable by pulsed-field gel electrophoresis (PFGE) and produced both Shiga toxins 1 and 2.

To identify risk factors, CDC, the Pennsylvania Department of Health, and MCHD conducted a case-control study among farm visitors during November 12--19. A confirmed case was defined as diarrhea in a person within 10 days of visiting farm A on or after September 1, with either E. coli O157 isolated from stool or HUS. A probable case was defined as diarrhea in a person within 10 days of visiting farm A on or after September 1. Controls also had visited farm A after September 1 but did not develop diarrhea within 10 days of the visit. Two controls per case were sought by sequential digit dialing and frequency matched by age group (i.e., <1 year, 1--4 years, 5--8 years, 9--12 years, 13--20 years, and >21 years). Fifty-one case-patients, or a parent or guardian for young children, and 92 controls were interviewed in the case-control study.

Case-patients were more likely than controls to have had contact with cattle (summary odds ratio [OR]=10.9; 95% confidence interval [CI]=1.7--70.7), an important farm animal reservoir for E. coli O157. Activities that promoted hand-mouth contact, such as nailbiting (summary OR=2.5; 95% CI=1.1--5.7) and purchasing food from an outdoor concession (summary OR=2.5; 95% CI=1.1--5.7), were more common among patients. Handwashing before eating was protective (summary OR=0.2; 95% CI=0.1--0.7). All 216 cattle on farm A were sampled by rectal swab, and 28 (13%) yielded E. coli O157 with a PFGE pattern indistinguishable from that isolated from patients. The same strain also was isolated from a railing surface. E. coli O157 was not isolated from 43 of the other animal species on the farm.

Among the 75,600 persons who visited farm A during the outbreak, most were preschool-aged or school-aged, groups at risk for serious E. coli O157 infection (1). No separate area was designated for interaction between visitors and farm animals. Visitors could touch cattle, calves, sheep, goats, llamas, chickens, and a pig and could eat and drink while interacting with animals. Handwashing facilities lacked soap and disposable towels, were out of children's reach, were few in number, and were unsupervised.

A total of 19,698 telephone calls were made to identify controls; 3497 household members were available. Household members were asked whether they had visited farm A since September 1 and whether they developed diarrhea within 10 days of the visit; 134 visited the farm during the outbreak, and 22 (16.4%) reported onset of diarrhea within 10 days of the visit. The expected rate of diarrhea from any cause in the general population during a 10-day period is approximately 7% (FoodNet Population Survey, unpublished data, 1998--1999). Because approximately 75,600 persons visited the farm during the outbreak, an estimated 7000 (9.4%) may have developed diarrhea associated with their visit. No further illness was reported after public access to animals was discontinued at farm A.

Washington

During May--June 2000, five persons with culture-confirmed E. coli O157 infection were reported to the Snohomish Health District (SHD). Isolates from these persons were indistinguishable by PFGE. Dates of illness onset were May 21--31, and patients ranged in age from 2 to 14 years (median: 7 years); three were male. All five patients reported abdominal cramping and diarrhea, and four reported bloody diarrhea. Three patients, aged 2--6 years, were hospitalized, and one developed HUS. Four patients attending three elementary schools had visited a dairy farm (farm B) on May 18 or 24. The fifth patient had not visited farm B but had developed diarrhea after a sibling became ill following a farm B visit. Approximately 300 persons visited farm B during the outbreak, primarily preschool- and kindergarten-aged children accompanied by adults.

On May 31 and June 1, an investigation of farm B by SHD and the Washington Department of Health revealed that children were allowed to handle young poultry, rabbits, and goats. Goats, chickens, and a calf were kept in pens and could be touched through a fence. Children brought their own lunches and ate approximately 50 feet from the penned animals. Five animal stool samples collected from the farm were tested for E. coli O157; all were negative.

Farm B recommended that visitors bring antibacterial wipes to wash their hands; the farm also provided a communal rinse basin. No signs were posted instructing visitors to wash their hands after touching the animals. No further illness was reported after prevention measures were instituted, including distribution of instructional material and installation of handwashing stations with soap and running water.

Reported by: R Gage, MSPH, A Crielly, MS, M Baysinger, E Chernak, MD, G Herbert, A Johnson-Entsuah, MPH, Montgomery County Health Dept, Norristown; G Fraser, C Rinehardt, M Solomon, G Withers, MS, R Berman, MS, Bur of Laboratories, Lionville; M Moll, MD, J Rankin, DVM, Pennsylvania Dept of Health. J Carroll, M Ettinger, MS, S Henderson, M Mismas, D Patel, T Reed, E Smith, J Wozniak, MS, D Toney, PhD, J Pearson, DrPH, Virginia Div of Consolidated Laboratory Svcs, Richmond. J Hofmann, MD, Snohomish Health District, Everett; J Grendon, DVM, J Kobayashi, MD, Washington Dept of Health. Animal and Plant Health Inspection Svc, US Dept of Agriculture. Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; and an EIS Officer, CDC.

Editorial Note:

The outbreaks described in this report were the first reported in the United States to be associated with direct transmission of E. coli O157 from farm animals to humans. An estimated 73,500 cases of illness, 2000 hospitalizations, and 60 deaths occur in the United States each year as the result of E. coli O157 infection (2); many E. coli O157 illnesses are associated with ingesting contaminated food or drink. However, during 1996 and 1997, visiting a farm with cows was identified as an important risk factor for E. coli O157 infection; 8% of persons aged >6 years with E. coli O157 infection reported visiting a farm with cows during the preceding 7 days compared with 1% of controls (3).

Two random-digit--dial telephone surveys of 9000 persons were conducted during 1996--1997 and 1998--1999; 2% reported having visited a petting zoo during the preceding 5--7 days (4,5). In 1999 in Ontario, Canada, an E. coli O157 outbreak among visitors to a petting zoo resulted in 159 illnesses (6). In the United Kingdom, farm visit-related outbreaks of E. coli O157 infections have been reported among children (7). Such outbreak have led to the development of guidelines to prevent E. coli-related illnesses in these countries (6,8).

Of the 44 state and territorial public health departments responding to a national CDC survey in June 2000, none had laws to control exposure of humans to enteric pathogens at venues where the public has access to farm animals, and no federal laws exist that address this public health issue. Following these U.S. farm-associated outbreaks, CDC, in collaboration with the Zoonoses Working Group, National Association of State Public Health Veterinarians, U.S. Department of Agriculture, Animal and Plant Health Inspection Services, and other groups, drafted measures to reduce the risk for farm animal-human transmission of enteric infections (see box).

Before July 1, 2001, comments about prevention measures can be mailed to Strategies, Foodborne and Diarrheal Diseases Branch, Division of Bacterial and Mycotic Diseases, CDC, 1600 Clifton Road, MS A-38, Atlanta, Georgia 30333, or e-mailed to zcn0@cdc.gov.

References

1. Boyce TG, Swerdlow DL, Griffin PM. Escherichia coli O157:H7 and the hemolytic-uremic syndrome. N Engl J Med 1995;333:364--8.
2. Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in the United States. Emerg Infect Dis 1999;5:607--25.
3. Kassenborg H, Hedberg C, Evans M. Case-control study of sporadic Escherichia coli O157:H7 infections in 5 FoodNet sites (California, Connecticut, Georgia, Minnesota, and Oregon). Presented at the 1st International Conference on Emerging Infectious Diseases, Atlanta, Georgia, 1998.
4. CDC. Foodborne diseases active surveillance network (FoodNet): population survey atlas of exposures: 1998--1999. Atlanta, Georgia: US Department of Health and Human Services, CDC, 1999.
5. CDC. Foodborne diseases active surveillance network (FoodNet): population survey atlas of exposures: 1996--1997. Atlanta, Georgia: US Department of Health and Human Services, CDC, 1997.
6. Warshawsky B, Henry B, Gutmanis I, et al. An Escherichia coli O157:H7 outbreak associated with an animal exhibit: Middlesex-London Health Unit Investigation and Recommendations, 1999. Available at http://www.healthunit.com/reportsresearch.htm. Accessed April 2001.
7. Milne LM, Plom A, Strudley I, et al. Escherichia coli O157 incident associated with a farm open to members of the public. Communicable Disease & Public Health 1999;2:22--6.
8. Health and Safety Executive. Avoiding ill health at open farms: advice to farmers. Sudbury, England: HSE Books, 2000; revised ed.,vol. 23. Available at http://www.hsebooks.co.uk/index2.html. Accessed April 2001.

Reducing the Risk for Transmission of Enteric Pathogens at Petting Zoos, Open Farms, Animal Exhibits, and Other Venues Where the Public Has Contact With Farm Animals

• Information should be provided. Persons providing public access to farm animals should inform visitors about the risk for transmission of enteric pathogens from farm animals to humans, and strategies for prevention of such transmission. This should include public information and training of facility staff. Visitors should be made aware that certain farm animals pose greater risk for transmitting enteric infections to humans than others. Such animals include calves and other young ruminant animals, young poultry, and ill animals. When possible, information should be provided before the visit.
• Venues should be designed to minimize risk. Farm animal contact is not appropriate at food service establishments and infant care settings, and special care should be taken with school-aged children. At venues where farm animal contact is desired, layout should provide a separate area where humans and animals interact and an area where animals are not allowed. Food and beverages should be prepared, served, and consumed only in animal-free areas. Animal petting should occur only in the interaction area to facilitate close supervision and coaching of visitors. Clear separation methods such as double barriers should be present to prevent contact with animals and their environment other than in the interaction area.
• Handwashing facilities should be adequate. Handwashing stations should be available to both the animal-free area and the interaction area. Running water, soap, and disposable towels should be available so that visitors can wash their hands immediately after contact with the animals. Handwashing facilities should be accessible, sufficient for the maximum anticipated attendance, and configured for use by children and adults. Children aged <5 years should wash their hands with adult supervision. Staff training and posted signs should emphasize the need to wash hands after touching animals or their environment, before eating, and on leaving the interaction area. Communal basins do not constitute adequate handwashing facilities. Where running water is not available, hand sanitizers may be better than using nothing. However, CDC makes no recommendations about the use of hand sanitizers because of a lack of independently verified studies of efficacy in this setting.
• Hand-mouth activities (e.g., eating and drinking, smoking, and carrying toys and pacifiers) should not be permitted in interaction areas.
• Persons at high risk for serious infections should observe heightened precaution. Farm animals should be handled by everyone as if the animals are colonized with human enteric pathogens. However, children aged <5 years, the elderly, pregnant women, and immunocompromised persons (e.g., those with HIV/AIDS) are at higher risk for serious infections. Such persons should weigh the risks for contact with farm animals. If allowed to have contact, children aged <5 years should be supervised closely by adults, with precautions strictly enforced.
• Raw milk should not be served.

Figure 1


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