First came the fires. Then, there was ash and contaminated water. Now, some survivors of the Southern California wildfires are dealing with outbreaks of norovirus and other stomach ailments at a shelter set up to help evacuees.

Norovirus, also known as the stomach bug, is spreading across the U.S. Here's what to know about the contagious virus and how best to prevent an infection.

Data from the Centers for Disease Control and Prevention show cases of norovirus, the highly contagious stomach bug, are surging in the U.S.

You can also get norovirus by touching objects or surfaces that are contaminated and then putting your hands in your mouth without washing them first. Hand-washing with soap and water is key, as hand sanitizer will not do the trick in the case of norovirus, experts say.

No. Hand sanitizer is simply not as effective against norovirus as it at killing other pathogens due to the virus's firm shell, Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, told TODAY.com recently.

Drivers of the increase in norovirus cases may include a new strain, but continued precautions, good hygiene, can help reduce risk.

What’s worse, there’s no real treatment for norovirus beyond getting plenty of rest and constant fluids infused with electrolytes. The virus typically only lasts one to three

Hand sanitizer alone isn't enough to protect you from norovirus, experts say. So it's important to know how to stay safe and wash your hands properly.

The cases mark the fourth norovirus outbreak on Holland America ships since early December, following others on its Eurodam, Rotterdam and Zuiderdam vessels. Other companies, including Cunard Line and Princess Cruises also saw outbreaks in recent weeks.

Norovirus, commonly called the stomach flu, is a gastrointestinal virus causing vomiting, diarrhea, abdominal cramping and a fever.