It’s been a while since I wrote about petting zoos. Part of the reason is that the state of petting zoos in this area has improved quite a bit over the past few years, so I haven’t been coming home from fairs or other events with a need to vent. However, improvements are not universal, and even with improved conditions, there are always going to be disease risks associated with petting zoos and other events where people have contact with animals.

This week’s edition of Morbidity and Mortality Weekly Reports (a rather gruesomely named but very interesting publication by the US CDC) describes a 2011 outbreak of E. coli O157 from a North Carolina State Fair. After receiving reports of infections in four people who had attended the fair, an investigation was launched. Here are the highlights:

• A total of 25 suspected cases were ultimately identified. (Usually, there are many more milder cases that go undiagnosed). Stool samples were collected from 19 of these individuals and the same strain of E. coli O157 was confirmed in 11 of them.
• Affected people ranged from 1-77 years of age.
• Eight people (32%) were hospitalized. Four of those had hemolytic uremic syndrome (HUS), a severe form of disease caused by E. coli O157.
• When compared to people who did not get sick, having visited one of the buildings were sheep, goats and pigs were housed for livestock competitions was the only risk factor identified. While the public was not supposed to have contact with animals in those buildings, 25% of people reported having had direct contact with animals anyway.

An investigation like this often can’t determine the source of the pathogen with 100% accuracy, because the investigation occurs after the fact (sometimes long after). That means the animals aren’t around anymore for testing, the area/fair may have been cleaned up already, and people may not completely (nor accurately) recall exactly what they did. Regardless, it’s quite suspicious that contact with this particular building was the root of the problem. How people became infected isn’t clear. Some had direct contact with animals, and that’s an obvious potential source. Cattle are the most common source of E. coli O157, but it doesn’t appear that any were present in the building. Sheep and goats are a more likely source than pigs. Other people could have been infected through contact with contaminated surfaces in the building, something that has been documented in other outbreaks.

After a large 2004 petting zoo outbreak at this same fair, the state passed a law (named Aedin’s Law, after a child who became seriously ill) that set strict requirements for animal exhibits where contact with the public is intended. This facility was not subject to Aedin’s Law because animal contact was not intended (even though it was apparently common) and a multiagency task force is looking into additional measures for exhibits where animal contact might occur.

Cost/benefit is an important issue when it comes to infectious disease control. There will always be some risk of disease when interaction with animals is allowed. We can take measures to reduce the risk, but never eliminate it. Therefore, the key is maximizing the benefit and minimizing the risk. Animal contact at fairs and similar events can be very rewarding for some people, so most people will accept some degree of risk. This outbreak involved a relatively small number of people, particularly when you consider approximately 1 million visitors attended the fair. The infection rate was really very, but with a potentially life-threatening disease, it’s not something that should be ignored.

As is the case here, infection control is often reactionary, with changes only taking place after problems occur. However, it’s good to see that actions are being taken (at least in NC) to reduce the risk of this happening again.