UNIVERSITY PARK, Pa. -- A new strain of norovirus, known as GII.4 Sydney 2012, is making the rounds this winter, causing a significant number of acute outbreaks. According to the U.S. Centers for Disease Control and Prevention, it has become the dominant strain, causing more than 140 reported outbreaks in the United States so far this year.
People should try to limit their exposure to norovirus and try to minimize its spread, advised an expert in Penn State's College of Agricultural Sciences.
"There are some important reasons that lead to so many people becoming ill from norovirus," said Martin Bucknavage, extension food safety specialist.
"One is this virus's low infectious dose. It is estimated that it may take less than 20 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. Norovirus is not related to the flu (or influenza), which is a respiratory illness caused by a different virus, and flu shots do not protect against it.
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 12 to 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 symptoms have subsided," Bucknavage said. "Contaminated surfaces must be cleaned using a strong chlorine bleach solution, one cup of bleach to one gallon of water. Cooking also will destroy the organism."
To learn more about norovirus, visit the Centers for Disease Control and Prevention website at http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus.htm.