The leading cause of foodborne disease is wreaking havoc this winter, according to a food-safety expert in Penn State's College of Agricultural Sciences, who says people should try to limit their exposure to Norovirus and try to minimize its spread.

In February alone, Norovirus caused more than 200 attendees at a cheerleader camp in Washington state to become ill. In St. Maarten, a cruise ship returned to port as 31 were afflicted. In Virginia, an elementary school was closed because so many students were sick. And in New Jersey, more than 400 college students became ill at three universities in the same county.

"There are some important reasons that lead to so many people becoming ill from Norovirus," said Martin Bucknavage, extension food safety specialist. "One is the virus's low infectious dose. It is estimated that it may take only 10 viral particles to make someone ill. Then, there is the ability of the virus to survive on dry surfaces for two weeks or more and in water for months."

The virus can be spread in contaminated food or water, from contaminated surfaces, directly from a sick person or from the intake of aerosolized droplets of vomitus.

The main symptom of Norovirus infection is another factor in its spread -- acute-onset vomiting. "This prevents people from becoming sick in a secure location," Bucknavage said. "Rather, rapid onset can occur at a dinner table, in a meeting or on the bus. People usually become ill within 24 hours of exposure, although longer incubation periods do occur."

Once someone is sick, they can experience symptoms for 24 to 72 hours and can remain contagious for up to three days, Bucknavage noted.

"Because of this short incubation time, low infectious dose and ease of spread, one can see why it spreads through a school or a cruise ship so quickly," he said. "While rarely fatal, people who become ill need to be sure to consume liquids so they don't become dehydrated."

The key to preventing infection is frequent, but correct, hand washing -- scrubbing hands with soap and warm water. In addition, it is important for people to stay home when ill, especially when they may have been exposed to someone who has had the illness.

"They also should stay home for at least 48 hours after systems have subsided," Bucknavage said. "Contaminated surfaces must be cleaned using a strong chlorine bleach solution, 1 cup of bleach to 1 gallon of water. Cooking also will destroy the organism."

To learn more about Norovirus, visit the Centers for Disease Control website at http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus.htm.