In the ongoing war between food businesses/events and epidemiologists, a battle over what caused 14 cases of salmonellosis in Devon (UK) has spilled into the BBC. A cluster of 14 Salmonella illnesses popped up back in April; 12 of the 14 attended and ate pork at charity hog roast. a fundraiser for the Hope Cove Life Boat. The even was put on to support the seaside village's emergency rescue vehicle.

Graham Phillips, chairman of the lifeboat committee, said: "We are sympathetic to people that were ill but we are confident we took every step possible to make sure the catering met health regulations.

"We would not set out to cause harm to people and we have bent over backwards to help the HPA in its investigation."

The HPA started an investigation after a number of complaints of food poisoning from people who said they had eaten from the hog roast.
But the HPA said there was no food left over from the event available for testing. It concluded: "It is not possible to confirm the source of the outbreak although the hog roast is the main link we identified between the cases."

A spokesman for South Hams District Council said the complaints had been "fully investigated" but it had decided there was not enough evidence to link the roast with the poisoning "beyond reasonable doubt."He said: "The key element for a successful prosecution would have been to confirm the strain of salmonella from the carcass of the roast pig, and then test victims to confirm it was of the same strain.

"However this was not possible because there was nothing left of the pig."
 
I can't seem to find a report online with odds ratios but there often isn't much food left to test in an outbreak. But we still trust the epidemiologists and the data they produce. Not many outbreaks would be solved if the strain had to be found in the food.

Lots of community dinners and charity events have been the source of a foodborne illnesses (here's an infosheet). As Rob Tauxe said in an article about new trends in foodborne pathogens, have created some of the easily traced foodborne illness outbreaks:

The traditional foodborne outbreak scenario often follows a church supper, family picnic, wedding reception, or other social event. This scenario involves an acute and highly local outbreak, with a high inoculum dose and a high attack rate. The outbreak is typically immediately apparent to those in the local group, who promptly involve medical and public health authorities. The investigation identifies a food-handling error in a small kitchen that occurs shortly before consumption. The solution is also local.

Part of the local solution is having volunteer food handlers trained to look for risks and reduce them.