It’s a disease humorist Stephen Colbert once poked fun at in this tweet: “Remember, if you’re in public and have the winter vomiting bug, be polite and vomit into your elbow.”

But officials at the California Department of Public Health say a sudden increase in norovirus infections is no laughing matter.

Already, the state has confirmed 32 outbreaks since Oct. 1 – far more than the nine cases reported last year at this time – and officials are warning Californians to wash their hands frequently to guard against infection.

Norovirus, also known as the winter vomiting disease, is a highly contagious virus that causes gastroenteritis, an illness that usually involves vomiting and diarrhea.

It is the most common cause of gastroenteritis in the U.S. and is responsible for approximately 20 million illnesses each year, with between 570 and 800 deaths reported annually, health officials said.

The virus can spread quickly in closed and crowded environments, such as hospitals, nursing homes, daycare centers, schools, cruise ships and food service settings such as restaurants.

Sickened people can still be contagious up to two weeks or more after recovery.

In the recent California outbreaks, the majority of cases have occurred at nursing homes and other long-term care facilities, with the remainder hitting schools and event centers, health officials said.

It can spread through direct contact with an infected person, consuming infected foods or liquids, or by touching a contaminated surface and then touching one’s mouth.

Symptoms usually begin 12 to 48 hours after a person has been exposed and last for one to three days.

The virus causes your stomach or intestines or both to get inflamed, according to the U.S. Centers for Disease Control and Prevention. This leads the sufferer to have stomach pain, nausea, diarrhea and vomiting. These symptoms can be serious for some people, especially young children and older adults.

HAND SANITIZERS NOT EFFECTIVE

“One of the most important things you can do to avoid norovirus and other illnesses this holiday season is to wash your hands frequently with soap and running water for at least 20 seconds,” Karen Smith, CDPH director and state public health officer, said in a prepared statement. “This is especially important after using the bathroom, changing diapers, and before preparing or eating food.”

Hand sanitizers are not effective against norovirus, Smith added.

Although it is called the winter vomiting disease, it can strike during all seasons.

In May, several patrons and employees at The Sky Room – an upscale Long Beach restaurant – fell ill in a norovirus outbreak. The restaurant closed for four days in order to sanitize the restaurant and bar.

The disease struck again in August at a Ventura County Chipotle restaurant, where an outbreak was believed responsible for sickening more than 60 customers. Managers were forced to shut down the restaurant, throw out the remaining food and disinfect all surfaces.

More recently, a norovirus outbreak may have sickened as many at 50 students at Chapman University. The gastrointestinal illness was first reported Dec. 2 by several students and grew rapidly.

The Orange County Health Care Agency investigated the cause of the outbreak and one source could have been the school’s only cafeteria, the agency said.

The cafeteria was closed and disinfected, the campus was swept down and the bathrooms and common areas were also cleaned.