Campylobacter outbreak among mountain bikers linked to mud

May 2008

ATLANTA — Contaminated mud ingested by mountain bikers during a lengthy race along sopping trails was the likely cause of a large Campylobacter jejuni outbreak in Canada in June 2007, according to a recent study.

The outbreak affected more than 200 of 785 participants in the 67-kilometer race in British Columbia on June 15, 2007. The outbreak came to public health officials’ attention after numerous racers posted illness symptoms on the race website and several racers developed diarrheal illness. An investigation ensued, and the researchers determined mud contaminated with animal feces was likely the cause of the outbreak.

“The evidence is pointing to mud,” Tammy L. Stuart, PhD, a field epidemiologist with the Public Health Agency of Canada, said. “In a fast-paced race, with a lot of mouth breathing under extremely muddy conditions after exceptional rainfall, everything came together to create risk.”

Stuart presented investigation results at the 2008 International Conference on Emerging Infectious Diseases, held here recently

The investigation was conducted by the Public Health Agency of Canada, Vancouver Coastal Health Authority and the British Columbia Center for Disease Control.

The Campylobacter organism is transmitted through ingestion. People are usually infected through contact with animal waste or through consuming contaminated food and water. Bears, horses, chickens and dogs were all reported on the trails prior to the race.

Bikers report illness

A retrospective cohort study was conducted to test hypotheses for potential exposure. To assess exposure, investigators set up a link on the race website to an online questionnaire about symptoms and mud exposure. Approximately 70% of race participants responded to the questionnaire.

Five percent of survey respondents met the laboratory-confirmed case definition (n=25) and 36% met the clinical definition (n=200). Fifty-seven percent of respondents met the well-case condition (n=312).

Only bottled water in paper cups was distributed to racers at stations along the course, and 25 racers reported illness but had not consumed water at any stations. Refilling personal water supplies at stations was not associated with illness.

Racers who reported inadvertently consuming mud had more than two times the risk for developing illness.

Mud and water samples collected from the race course were tested for Campylobacter, generic Escherichia coli and total coliform counts. The results for Campylobacter were negative. The researchers said the negative samples were not unusual because samples were taken three weeks after the race. Mud samples were positive for generic E. coli, and coliform counts in some samples exceeded 24,192/100 mL.

For more information:

• Stuart TL, Sandhu J, Stirling R, et al. An investigation points towards contaminated mud as the source of Campylobacter jejuni outbreak associated with a mountain bike race; British Columbia, Canada, June-July 2007. Presented at: The International Conference on Emerging Infectious Diseases 2008; March 16-19, 2008; Atlanta.