WASHINGTON (CNN) -- The "stomach bug" is spreading again in the U.S. Norovirus involves severe upset stomach, diarrhea and fatigue, and this illness is a bit tougher than your standard flu.
There have been several major norovirus outbreaks on cruise ships in recent years
The norovirus is spread through food or drink that has been contaminated, and also through touching contaminated surfaces or objects.
Symptoms include abdominal cramps, vomiting, nausea, diarrhea and fatigue.
"It's very contagious. There are multiple epidemics of it. Other than cleaning the areas, there's not a whole lot people can do about it," Dr. Gary Simon with George Washington University Hospital said.
The norovirus is so contagious because it's so hardy. Typical hand sanitizers and disinfecting wipes do not protect against the illness. What does work is soap and water and a bleach-based cleaning solution.
Most people infected with this illness recover after a few days, but in rare cases, it can be fatal -- particularly for the very old and very young and those with weaker immune systems.
According to the CDC, there are more than 20 million cases of the norovirus each year, resulting in about 800 deaths in the U.S.
"It's so infectious and requires such a low concentration of virus, it's rapidly spread through a population. That's why you see outbreaks on cruise ships, in dormitories, in places where people are in close contact with one another," Dr. Simon said.
According to the CDC, to protect against norovirus:
- Wash your hands often
- Wash fruits and vegetables
- Cook shellfish thoroughly
- Clean surfaces and wash soiled laundry
- When you're sick, don't prepare food or care for others
With the flu, you can get a flu shot. But there isn't a vaccination right now for the norovirus and no way to treat it. So the best bet is prevention.