Contaminated mud blamed for bug that hit 161 bikers

Organisers pledge action after outbreak at Merida Marathon

Many riders caught a mystery bug at the Merida Marathon round in Builth Wells

Organisers have pledged to take action after more than 150 British mountain bikers were laid low with a mystery illness after a marathon race.


An official report into the outbreak of vomiting and diarrhoea which followed the Merida Bikes MTB Marathon Series round in Builth Wells, Wales, has concluded that it was probably caused by mud contaminated with sheep droppings.

The National Public Health Service for Wales (NPHS) and Environmental Health officers at Powys County Council launched an investigation following the event on 5 and 6 July.

Officials emailed 664 riders who took part and received 355 responses. Of those, 161 reported symptoms such as tiredness (159), diarrhoea (151) and abdominal pain (131). Only six non-riders were reported to have fallen ill

The investigators concluded that the outbreak was probably caused by a bug called campylobacter, spread to the cyclists by mud which was contaminated with sheep faeces. Heavy rain meant the course was awash with slippery liquid mud which splashed onto riders’ hands and water bottles.

The report acknowledged that, given the nature of mountain bike events, it would be impossible to eliminate the risk of catching such an infection, but made the following recommendations:

  • Participants should avoid using soiled drink and food containers
  • Pre-packaged food should be eaten out of the wrapper
  • Where possible, hands and utensils should be washed before consuming food and drinks
  • No open food should be served at events.
  • Drinks produced in large volumes for consumption by participants should be dispensed using a method which does not require the repeated immersion of utensils.
  • Organisers should consider providing facilities to wash hands and water bottles with clean, running water
  • Wherever possible, courses should be re-routed to avoid areas which are heavily contaminated with animal faeces
  • Mountain bikers, particularly those who are vulnerable to infection, should be alerted to the potential risk of acquiring zoonotic illnesses from participation in events which cross land used by agricultural and other animals.

Organiser Michael Wilkens, of MJW Marketing, said he was glad the cause of the illness had been confirmed, and said steps had already been taken to limit the chances of another outbreak at future events. He said incidences of campylobacter were not uncommon among walkers and mountain bikers, but admitted the severity of the outbreak had taken organisers by surprise.

He said, “I’m really sorry that this happened. [This bug] is really nasty, not a pleasant thing to go through. We will do our utmost to prevent it happening again in the future. I hope it hasn’t put people off.

“In terms of the recommendations, we either already have them in place or are putting them in place. When it comes to drinks containers, we already use buckets with taps in the sides. We will put washing facilities up and make riders aware [of the risk from infected mud].

“We are also looking into alternative venues to Builth. In April there’s no problem because the sheep are only just going back into the fields, but at the second Builth round in the summer, if it does start raining heavily it’s difficult to change the course.”

Michael suggested that when there was heavy rainfall at events, riders could take precautions such as using hydration packs rather than water bottles and fitting a Crud Catcher to their bike.

Dr Siân Griffiths, of the NPHS, said, “We have been delighted with the help we have received from the mountain bikers when investigating this outbreak of illness. We would also like to thank the race organisers for their co-operation and our colleagues in Environmental Health. We hope this report and the recommendations within it will help reduce the risk of something like this happening again.”

Campylobacter is one of a group of diseases known as zoonoses, meaning that they move into humans from an animal source. The bacterium can cause diarrhoea, abdominal pain, fever and nausea. Most cases settle within two to three days, although symptoms may last up to a week. To comment on the report, email

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