An unwelcome visitor has made its annual appearance in Helena for the holiday season: norovirus.

With winter weather confining people to enclosed indoor spaces, the chances of coming in contact with norovirus -- also commonly called the "stomach flu" -- increases.

But according to local health officials, people can take precautions during this holiday season and all winter long to protect themselves from this highly contagious virus.

Norovirus causes nausea, abdominal cramps, vomiting and diarrhea. People are exposed to the virus by food, water or other things that are put into the mouth such as hands, toys, pacifiers, utensils and cigarettes.

According Bonnie Bernard, communicable disease specialist with the Montana Department of Public Health and Human Services, clusters of norovirus have been reported around the state, including Helena. A cluster is defined as several cases in a common venue -- such as a hospital, day care or event -- in a short period of time.

Bernard said that frequent and thorough hand washing is the best way to keep the virus from spreading.

"That one thing will go a long way to prevent you from getting the stomach flu," Bernard said.

According to Laurel Riek, environmental Health Specialist at the Lewis and Clark City-County Health Department, studies by the Centers for Disease Control have indicated that roughly 40 percent of norovirus cases were attributed to contaminated food.

"Parties can bring a lot of hands in contact with displayed foods," Riek said.

In addition, a person may also be exposed if they contact the virus while it is in the air contained in droplets. These droplets get into the air during vomiting, or when a toilet is flushed after an ill or recently ill person uses it. These droplets then land on surfaces including; sinks, tables, counters, toys, door handles, light switches and faucets creating easy opportunities for exposure.

People who suspect they have norovirus can help stop its spread by:

- staying home while they have symptoms and trying to avoid direct contact with other people for at least 48 hours after symptoms have gone.

According to Bernard, staying home from work is especially important for people who work in food services, health care or day care.

- Do not prepare food while you have symptoms and for at least 48 hours after you recover from the illness. Riek adds: "Since the virus must be consumed, the easiest way to share it is with contaminated food."

- If a party is scheduled for your home, cancel, move or postpone until you have recovered. Also, refrain from attending parties if you are sick.

You can protect yourself and your family from contracting these viruses through good sanitary procedures:

- Wash hands with soap and water thoroughly and frequently, especially before eating or otherwise touching your mouth and after using the restroom. Instant hand sanitizers don't protect you from this virus.

- Disinfect surfaces with a chlorine bleach solution. Rinse off with clean water. Use 5 tablespoons per gallon of water for food or mouth contact items; 1/3 cup bleach per gallon of water for nonporous surfaces; 1 2/3 cup bleach per gallon for porous surfaces, such as wooden floors

- Immediately launder any soiled clothes or bedding.

People may start to feel sick 12-48 hours after exposure and the illness may last from 12 hours to five days.

Rarely do people need medical attention, but the very young, the elderly and those with weakened immune systems are at risk for dehydration, that can lead to severe illness or death.

"The single most important thing you can do to protect yourself against norovirus is to wash your hands with soap and water. To protect the rest of the community, please stay home if you are sick and do not prepare food for your friends and family," Riek said.

Features editor Joe Menden: joe.menden@helenair.com or 447-4087