More than 160 mountain bikers at a Powys event fell ill after coming into contact with mud contaminated with sheep droppings, a report has found.
Cyclists reported vomiting and diarrhoea to health officials after taking part in the Builth Wells Mountain Biking Marathon in Powys.
The National Public Health Service for Wales (NPHSW) found the cyclists had probably ingested the bacterium campylobacter in the mud in July.
The report recommended participants eat out of wrappers at future events.
It also said organisers should consider rerouting courses to avoid areas heavily contaminated with droppings, and warn participants of the possible risks.
The report concluded the danger was limited to participants who had accidentally ingested the infected mud. Heavy rain had made the situation worse by increasing the amount of liquid mud on the course.
The NPHSW was alerted to the outbreak by a participant who told them he knew of eight people who had become unwell after the event.
It sent out questionnaires to the 664 people who had taken part and 355 responded, with 161 reporting vomiting and diarrhoea.
Dr Siân Griffiths of the NPHSW thanked the race organisers and the Environmental Health Department at Powys County Council for their co-operation in the report.
“We have been delighted with the help we have received from the mountain bikers when investigating this outbreak of illness,” she said.
“We hope that this report and the recommendations within it will help reduce the risk of something like this happening again.”
