The source of last month’s outbreak of an intestinal parasite at a charity food event in Sarnia (Ontario, Canada) remains a mystery.

Public health officials questioned 286 of the more than 300 people who attended the Chef’s Challenge and found 206 became ill, said Andrew Taylor, Lambton County’s general manager of public health services.

Taylor said they also spoke with the event’s caterers and tested food samples.

“We were awaiting lab results until the end of last week and we were hoping that would be the home run,” he said, adding the results weren’t conclusive.

“The perfect investigation is where there’s illness, you identify the parasite at the source of the illness and then you link it to the food,” he said. “We have everything except the link to the food.”

Cyclospora is usually found in imported produce and contaminated irrigation water is often to blame, Taylor said.

A barfblog.com reader previously noted cyclospora is more of an environmental contamination issue than a hygiene issue. If the suspect food was something like raspberries, they are difficult to wash; basil or lettuces may be easier to wash but have a very large surface area and cyclospora is very very sticky. As with many other fresh produce outbreaks prevention on the farm is the best way to reduce risk.