Norovirus cases are on the rise in the US, CDC data show

Case of a miserable one stomach bug is increasing in parts of the United States this winter, according to government data.

The latest figures from the US Centers for Disease Control and Prevention show that there were 91 outbreaks of norovirus reported during the week of December 5, up from 69 outbreaks the last week of November.

Figures from recent years show a maximum of 65 outbreaks reported during the first week of December.

A norovirus infection is characterized by sudden vomiting and diarrhea. Outbreaks are often seen on cruise ships, in gathering situations such as nursing homes and prisons, as well schools and places where people are close to each other.

Here are a few things to know about the virus.

What is norovirus?

Norovirus is the leading cause of foodborne illness in the United States, responsible for 58% of such infections acquired in the country each year, according to the CDC.

Norovirus infections are caused by a group of viruses that spread easily, with as few as 10 viral particles capable of making someone sick, health experts say.

There are about 2,500 norovirus outbreaks reported annually in the United States. Outbreaks can occur throughout the year, but are most common from November to April.

Along with vomiting and diarrhea, common symptoms include nausea, abdominal pain, body aches, headache, and fever.

How do you get it?

Most norovirus outbreaks occur when people who are already infected spread the virus to others by direct means, such as sharing food or eating utensils. Outbreaks can also spread through food, water or contaminated surfaces.

How long will you be sick?

Illness caused by norovirus typically starts suddenly with symptoms developing 12 to 48 hours after exposure to the virus. Most people feel better within one to three days and make a full recovery.

But with 19 to 21 million illnesses each year in the United States, norovirus nonetheless causes an average of 900 deaths and 109,000 hospitalizations annually, mostly among adults 65 and older. It also leads to 465,000 emergency room visits, mostly involving young children.

Who is at risk?

People of all ages can be infected and become ill from norovirus. Young children, elderly people and those with compromised immune systems are most at risk, with dehydration from vomiting and diarrhea being the main concern.

There is no medicine to treat norovirus. Rehydration is recommended by drinking water and other liquids, with the exception of coffee, tea and alcohol.

Anyone suffering from dehydration should seek medical attention. Symptoms of dehydration include a decrease in urination, dry mouth and throat, and dizziness when standing. Dehydrated children may be unusually sleepy or fussy and cry with few or no tears.

How can I protect myself?

Thorough and frequent hand washing is the best defense against norovirus during the peak winter season, and scrub your hands with soap and warm water for 20 seconds before meals.

Scrubbing surfaces with household disinfectants can also help.