As Iditarod mushers were headed for Nome on Tuesday, public health officials worried that a highly contagious virus is headed there with them.

Health officials have been investigating an outbreak of norovirus since early March, days before the Iditarod began. Fifteen race officials, many of them pilots, had attended a meeting in McGrath at the end of February, and at least nine developed vomiting, abdominal cramps and diarrhea soon after, said Dr. Marc Chimonas and Dr. Joe McLaughlin, epidemiologists with the state health department. To prevent the virus from spreading, McLaughlin spoke to the racers about the illness at the mushers meeting March 4.

By the end of the first full week of the race, a McGrath physician assistant informed the state Section of Epidemiology that several more Iditarod race officials had developed similar symptoms. Last Friday, McLaughlin, Chimonas and an employee of the state Department of Environmental Conservation traveled up the Iditarod trail to McGrath, Cripple and Ruby looking for more illness and letting the communities know about the moving outbreak.

By Tuesday evening, the state reported about 47 people who'd suddenly developed vomiting or diarrhea along the trail between Feb. 15 and Tuesday. Most of the people started having symptoms in McGrath, but a few became ill in Anchorage and Ruby, all points along the Iditarod Trail, McLaughlin said. One person was hospitalized in Anchorage, but has since improved. No one has died, he said.

Twenty-five of the 47 cases were people affiliated with the Iditarod, McLaughlin said. Several were veterinarians, he said, and two were mushers.

Health officials didn't name the mushers. Chimonas said one musher had recovered and continued the race, but he didn't know the status of the other musher Tuesday.

The outbreak is not over, McLaughlin said, and state health officials worry that more cases will develop in Nome as people arrive there for the race's conclusion and Saturday's mushers banquet. State health officials reported the first case of illness in Nome Tuesday.

"What we're worried about, frankly, is we just don't want to see a large outbreak occur in Nome at the end," said McLaughlin "We're doing everything we can to prevent that from occurring."

McLaughlin will head to Nome on Friday to talk with people, restaurants and hotels about preventing the spread of norovirus. Nurses with the Norton Sound Health Corp. also will spread the message.

Norovirus was formerly known as the Norwalk virus and has been linked to outbreaks on cruise ships.It is spread by person-to-person contact, or eating and drinking food that's been contaminated by feces. People can spread the virus for at least four days after their symptoms resolve, McLaughlin said.

To prevent spreading the highly infectious virus, McLaughlin recommended thoroughly washing hands with soap and water after going to the bathroom and before preparing food. If water is not available, he suggested using the alcohol-based hand sanitizers.

People should clean and disinfect frequently touched surfaces -- such as counter tops, hand rails and doorknobs -- with a solution of a half cup chlorine bleach per gallon of water. Surfaces contaminated with vomit or diarrhea should be disinfected with a solution of 2¹/₂ cups of bleach per gallon of water. Those doing the cleaning should wear gloves and wash hands afterward, McLaughlin said.

McLaughlin said health officials are asking ill spectators and staff to stop traveling the trail.

"We're asking them not to progress forward along the trail because of the threat of spreading (the virus) further," he said.

If mushers become ill, they should be evaluated by health care providers before advancing, he said.

Daily News reporter Ann Potempa can be reached at 257-4581 or apotempa@adn.com.