The U.S. is seeing a "quad-demic" as cases of COVID-19, flu, RSV and norovirus spread at the same time. Experts said this is what you need to know.

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.

After the holiday season and an uptick in travel, California is seeing a rise in respiratory illnesses, prompting health experts to talk of a potential “quad-demic.” The term refers to the simultaneous spread of four major viruses: COVID-19,

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.

"It is too early to tell if this strain is associated with more severe norovirus disease but likely lower population immunity is the reason for the early surge of an otherwise seasonal increase of this virus," Jan Vinjé, head of the CDC's CaliciNet system, told CBS News in an email.

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

Flu season is here in California, but other illnesses are in full swing in the Golden State. Here are the symptoms and how long you're contagious.

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.

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.

Multiple norovirus outbreaks have been reported in Chicago during the month of January, the Chicago Department of Public Health confirmed this week.

The U.S. is seeing a "quad-demic" as cases of COVID-19, flu, RSV and norovirus spread at the same time. Experts said this is what you need to know.