Beware of an uninvited guest at your table this holiday season — norovirus.

Minnesota health officials said Monday that they're coping with what's likely to be the second-worst start ever to the peak season for the stomach bug, also called viral gastroenteritis. The disease, which causes diarrhea and vomiting, is spread through personal contacts and careless food preparation.

"It's definitely one of the worst seasons we've seen in quite a while," said Doug Schultz, a spokesman for the Minnesota Department of Health. "One of my staff said, 'We're drowning in norovirus.' "

Seasonal influenza is also off to a harsh start this year, but it is a different virus and is characterized by cough, fever and headaches — not digestive problems.

About 40 outbreaks of norovirus have been reported to the Health Department since Nov. 1, with about half occurring in the first two weeks of December, said Dr. Kirk Smith, food-borne disease supervisor for the department. He said only a fraction of the cases likely get reported.

The worst season on record, which began in 2006, saw 67 outbreaks reported in November and December and was blamed on two new strains of the virus. The strain wreaking havoc this year has been around for a year or two, so it's not clear what's driving the increase in cases. No one knows why, but norovirus infections tend to peak in late fall and early winter.

Norovirus sickens an estimated 20.8 million people a year in the United States, with slightly more than a quarter of the illnesses traced to contaminated food. That makes it the most common agent for food-borne illnesses.

The virus, which spreads from fecal contamination, can be largely prevented by thorough hand-washing with soap after using the restroom as well as before cooking and eating.

Alcohol sanitizers don't do so well with the persistent bug, Smith said.

A person who picks up norovirus from a contaminated surface can deposit it on seven more surfaces before it's too diluted to do harm, Smith said. Another person can pick it up and deposit it on a surface that then can contaminate another person. That process can go through four "generations" of carriers, he said.

And when an infected person prepares food for other people, it can lead to a major food-borne outbreak.

"With norovirus, typically, you feel like you want to die for that day or two," Smith said. "But it really is, by and large, a self-limited illness."

Hospitalizations are rare, he said, and deaths are rarer still.

Even so, infants, the elderly and those with compromised immune systems are especially vulnerable and should seek health care in extreme cases.

If you get sick, Smith said, drink plenty of liquids and rest, stay away from others and don't prepare food for anyone.

Dan Browning • 612-673-4493