Many people develop a vague rash and fever after a Tough Mudder event

California health officials issued a statement Advisor After several people who participated in the Tough Mudder Race and obstacle course competition this past weekend developed hitherto unexplained symptoms.

The Sonoma County Health Services Department (SDHS) said it received multiple reports of rash, fever, muscle aches, nausea, and vomiting among those who participated in the event at Sonoma Raceway, a motorsport track located 30 miles north of San Francisco, on the 19th and 20th. August.

“The grueling mud race involves intense exposure of the skin to mud. Most affected persons develop a pustular rash, fever, muscle pain and headache,” reads the health warning, which was published on Wednesday.

According to the SDHS, the symptoms can be caused by “a simple illness called swimmer’s itch,” also known as atopic dermatitis, which is caused by an allergic reaction to certain microscopic parasites, according to the SDHS. Centers for Disease Control and Prevention.

Parasites live in some species of birds and mammals. If their eggs find their way into the water and hatch, the larvae can infect certain types of water snails, which in turn release microscopic larvae that can burrow into human skin and cause symptoms, including rashes.

However, SDHS said people may have a staph infection, or a more serious infection from a bacterium known as Aeromonas hydrophila.

Staph infections are caused by staph bacteria and usually cause only minor skin infections, according to the Mayo ClinicAlthough the infection can become more serious if the bacteria enters the bloodstream and travels to the host’s bones, heart, or lungs.

However, Aeromonas hydrophila is commonly found in freshwater or wastewater, and although rare, it can infect humans, with reports of complications including diarrhoea, kidney disease and hemolytic uremic syndrome – which occurs when small blood vessels in the kidneys are damaged and inflamed, which may lead to kidney failure — meningitis, sepsis, according to the Public Health Agency of Canada.

“If you run a race and have a rash with a fever or other symptoms, please see your medical provider, or your local emergency department if you do not have one. You may want to take this advice with you. The incubation period is 12 to 48 hours, states the SDHS health advisory.

SDHS did not immediately respond to ABC News’ request for comment, nor did the organizers of the Tough Mudder event.

Tough Mudder co-host Nicole Villagran told her local ABC affiliate Kgo TV She did not participate in any obstacle course but still found bumps on her body the next day.

“You wake up the next day and you’re like, ‘What’s all this on my arm? What’s going on here?'” she said. “And it’s on my arm. That’s where I’d dig and do the military crawl, and it’s on the inside of my knee where I’d push it too.”

Fellow participant Curtis Vollmar told KGO TV that 12 of the 13 people who participated in the Tough Mudder event also experienced symptoms, although they faded away.

“It’s pretty much gone,” he said, gesturing to his arms. “You can’t really see much of it, but from the elbows up and the knees down, I was covered in these red pimple-like things.”