Tis the season to wash your hands and watch what you eat.

Norovirus, a vomit- and diarrhea-inducing stomach bug, is sickening Floridians through tainted surfaces and contaminated shellfish.

The Sunshine State is one of 12 in the U.S. with a high number of confirmed outbreaks of the virus. Anyone suffering from a bout of the nasty, extremely contagious virus, beware: it has no specific treatment and typically has to run its course.

Also of note: On average, one infected person will infect two to seven other people.

“It only takes a few virus particles to cause infections, so it doesn’t take much exposure to get sick from norovirus,” said Margaret Gorensek, an infectious disease doctor at Holy Cross Health in Fort Lauderdale.

Norovirus can spread through food, touch, and air particles.

Earlier this week, the Food and Drug Administration issued two separate seafood recalls in states over potential norovirus contamination.

On Monday, the FDA warned restaurants, food retailers, and consumers in seven states, including Florida, not to eat or sell oysters and Manila clams from Rudy’s Shellfish in Washington. Two days later, the agency issued another recall in 15 states, including Florida, for oysters sold as Fanny Bay, Buckley Bay, and Royal Miyagi Oysters from British Columbia, Canada. Both recalls cited potential contamination with norovirus. The recall did not mention any reported illnesses connected to the oysters and clams.

Shellfish can absorb untreated human sewage containing norovirus; when humans eat the contaminated shellfish, they can become infected.

Most people experience symptoms 12 to 48 hours after eating contaminated food. The common symptoms are nausea, stomach pain, fever, headaches, and body aches.

When norovirus spreads through direct contact, it tends to be from shaking hands or touching contaminated surfaces and then putting your hand in your mouth. That type of spread often happens in restaurants, schools, and on cruise ships.

This month, the norovirus has been wreaking havoc on cruise ships. So far, in December, four ships have reported outbreaks, with one ship reporting more than 100 passengers falling ill,  according to the Centers for Disease Control & Prevention.

There have been 13 reported norovirus outbreaks on cruise ships this year, but this is the first time the virus has been confirmed on three ships within a single month, and suspected on a fourth. Those ships include Holland America’s Zuiderdam and Rotterdam and Princess Cruise’s Ruby Princess. The most recent outbreak was on Cunard’s Queen Mary 2, and while passengers experienced norovirus-like symptoms the exact gastrointestinal illness has not been confirmed.

In all cases, the cruise lines isolated ill passengers and crew and increased cleaning and disinfection procedures.

Gorensek at Holy Cross said norovirus is seasonal and often spreads more in the winter. “We usually see it more whenever people are spending time together.”

She said that anyone handling food for holiday meals without thoroughly washing their hands can quickly spread it.

Unlike other viruses, norovirus is hard to kill on surfaces or hands.

“A quick dose of hand sanitizer doesn’t work, only soap and water,” she said. “On surfaces, bleach-based products are best.”

Noroviruses also are relatively resistant to heat and can survive temperatures as high as 145 degrees Fahrenheit.

Inhaling airborne norovirus particles can happen — potentially in an airplane’s bathroom — but that method of spread is less common than contact with contaminated surfaces or food.

Anyone who gets norovirus needs to be careful with staying hydrated. Gorensek recommends Pedialyte, Gatorade or broth. “Water isn’t good because it doesn’t give you the necessary electrolytes,” she said.

Young children and anyone with an underlying condition need to be particularly cautious, she said, because “they are susceptible to dehydration and are most at risk.”

South Florida Sun Sentinel health reporter Cindy Goodman can be reached at cgoodman@sunsentiel.com.