Topeka ? A common virus was to blame for illnesses that afflicted several bicyclists during last week’s Biking Across Kansas tour, health officials said Wednesday.

Twelve bicyclists on the tour tested positive for norovirus, a virus that is easily spread, and dozens got sick, according to the Kansas Department of Health and Environment.

“We’re continuing our investigation to determine the scope of these illnesses and what factors may have contributed to the outbreak,” said Dr. Howard Rodenberg, director of the KDHE Division of Health and State Health Officer.

Both norovirus and rotavirus illnesses cause nausea, vomiting, diarrhea and some stomach cramping. Some also experience a low-grade fever, chills, headache, muscle aches and fatigue. Symptoms usually last about one or two days.

Several cases of gastrointestinal illnesses were reported in several counties among bicyclists on the tour.

More than 800 cyclists participated in the eight-day tour, which started June 10 in Johnson City on the Kansas-Colorado border and ended Saturday in the southeast Kansas town of Arma.

Biking Across Kansas officials said they already were considering ways to improve hygiene along the route next year.

“I take this pretty seriously,” executive director Charlie Summers said.