Dec 23, 2004 (CIDRAP News) – A recent outbreak of E coli O157:H7 infections was traced mostly to a petting zoo at the North Carolina State Fair, even though the zoo had posted signs and provided facilities to promote hand hygiene.
The outbreak in October and November involved 108 likely and confirmed cases, many of them in children younger than 6 years, according to the North Carolina Department of Health and Human Services (NCHHS). The outbreak led to 15 cases of hemolytic uremic syndrome, a life-threatening kidney complication of E coli O157:H7 infection in children.
After recognizing that most of the people with symptoms had attended the fair, investigators compared case-patients with healthy fair visitors to identify possible causes of the outbreak, the NCHHS said in a news release. The patients and controls were asked about exposure to the fair's two petting zoos, other animal exhibits, food and drinks sold at the fair, and possible household sources of E coli.
The comparison pointed to the Crossroads Farm Petting Zoo as the likeliest source of infection for most of the patients, officials said. Contact with manure at the petting zoo stood out as a risk factor: among children under age 3 who had visited the zoo, case-patients were more than seven times more likely to have had contact with manure than controls were.
In an effort to prevent illness, the zoo had followed guidelines from an organization of public health veterinarians, which included posting signs and providing hand sanitizing stations, the NCHHS said. But information from interviews indicated that hand hygiene failed to protect people from infection.
"Exposures from direct contact between petting zoo visitors and animals or manure might have already led to infection before hand-sanitizer use," or patients might have picked up contamination on skin areas where subsequent hand cleansing failed to remove it, the department said.
Laboratory tests supported the results of the case-control study. In 33 of the 43 confirmed cases, the E coli strain had the same DNA fingerprint (pulsed-field gel electrophoresis pattern) as E coli samples from the petting zoo. Testing of environmental samples from the petting zoo showed that most of the samples containing E coli O157:H7 came from areas where people could pet sheep and goats.
The NCHHS concluded that most patients fell ill as a result of visiting the petting zoo, though some probably picked up the infection elsewhere at the fair.
"In light of the investigation, we recommend restricting direct contact with animals, reducing fecal contamination, and reducing crowding in petting zoos in addition to existing recommendations to prevent future E. coli O157:H7 infections," the NCHHS said, citing recommendations from the National Association of State Public Health Veterinarians (NASPHV). "These recommendations are particularly pertinent for young children and others with reduced immunity to infection."
The North Carolina outbreak is one of several E coli O157:H7 outbreaks linked to petting zoos or farms in recent years. A petting zoo in Ontario was found to be the source of 159 cases in 1999, and 51 cases were traced to a Pennsylvania dairy farm in the fall of 2000, according to the US Centers for Disease Control and Prevention (CDC).
April 20, 2001, CDC report on E coli cases associated with farm visits in Pennsylvania and Washington state