A norovirus, or gastroenteritis, outbreak is spreading across Southwest Montana.

Since early September, several hundred people have experienced vomiting, diarrhea and nausea lasting 24 to 48 hours. In those outbreaks where laboratory testing was performed, norovirus was found to be the cause of the illnesses, according to the Department of Public Health and Human Services.

Noroviruses are the most common of the viruses that cause gastroenteritis. Sometimes the illness is called “food poisoning” or “stomach flu”, although this illness is not related to influenza viruses which cause respiratory illness. There is no specific treatment for this illness and most people recover in one to three days. It can last longer and be more severe in young children, the elderly, or people with other health conditions.

The virus is highly contagious and can spread rapidly. A person can become ill by ingesting the virus from contaminated food or water or by close contact with someone who is ill. Touching surfaces or objects that are contaminated with norovirus, and then transferring the virus hand to mouth is another common way of becoming infected.

“To protect yourself and others it is important to wash your hands thoroughly with soap and water often, stay at home if you are ill with diarrhea, vomiting, or nausea, and never prepare food for others if you sick with any of these symptoms,” said DPHHS Director Anna Whiting Sorrell.

Tips to prevent the spread of norovirus:

. Practice proper hand hygiene: Wash your hands carefully with soap and water, especially after using the bathroom or changing diapers and always before eating or preparing food. Alcohol-based hand sanitizers (containing at least 62 percent ethanol) may be a helpful addition to hand washing, but they are not a substitute for washing with soap and water.

. Take care in the kitchen: Carefully wash fruits and vegetables, and cook oysters and other shellfish thoroughly before eating them.

. Do not prepare food while ill: People who are infected with norovirus should not prepare food for others while they have symptoms and for three days after they recover from their illness.

. Clean and disinfect contaminated surfaces: After an episode of illness, such as vomiting or diarrhea, immediately clean and disinfect contaminated surfaces by using a bleach-based household cleaner as directed on the product label or a solution made by adding 5-25 tablespoons of household bleach to one gallon of water.

. Wash laundry thoroughly: Immediately remove and wash clothing or linens that may be contaminated with vomit or fecal matter. Handle soiled items carefully-without agitating them-to avoid spreading virus. They should be laundered with detergent at the maximum available cycle length and then machine dried.