The return of cold weather brings the familiar burdens of flu and norovirus.

Both illnesses are highly contagious. And each one affects tens of millions of people every year in the United States.

LISTEN UP: Add the new Michigan Medicine News Break to your Alexa-enabled device, or subscribe to our daily audio updates on iTunes, Google Play and Stitcher.

Do you know the difference between the two?

Although some people may refer to norovirus as "stomach flu," it isn't technically the flu. It's a quick yet uncomfortable bout of gastrointestinal illness.

Influenza, on the other hand, is an infection of the respiratory system that may take more time to surface — and, depending on its severity, to shake off.

"The symptoms are different," says Preeti Malani, M.D., chief health officer at the University of Michigan. "From a contagiousness standpoint, I'd say norovirus concerns me a little more.

"Once it sets up in a school, residence hall or hospital ward, it can be really difficult to get control of."

That worry resurfaced this week when Michigan health officials cited increased norovirus activity in the state. Meanwhile, the Centers for Disease Control and Prevention has confirmed widespread flu activity in 24 states so far in 2019.

Malani, who is also a professor of infectious disease and internal medicine, spoke about how to stay healthy this season.

Norovirus infection symptoms

Signs of norovirus include nausea, vomiting, diarrhea and abdominal pain. Some patients also experience headache, fever and aching muscles.

MORE FROM MICHIGAN: Sign up for our weekly newsletter

The virus is found in vomit or feces. Even in trace amounts, it can linger on contaminated objects or surfaces for weeks.

As a result, "try to avoid putting your fingers in your mouth or touching your eyes and nose as much as you can," Malani says. A person with dirty hands can unknowingly transmit norovirus onto food, putting anyone who consumes it at risk.

The signs of flu are usually marked by symptoms such as fever, headache, sore throat, stuffy nose, body aches and loss of appetite — ailments that Malani says "most people would associate with a cold."

The flu spreads mainly from droplets that travel when you cough, talk or sneeze.

How noroviruses are diagnosed

Most people won't need medical care for norovirus; recovery can occur at home.

To confirm norovirus, it's helpful to find out if others in recent close contact — day care classmates or roommates, for example — have also become sick. Multiple cases might prompt a school or workplace to close temporarily to stem the tide.

SEE ALSO: What You Should Know About E. Coli Outbreaks

"It doesn't take a lot to spread this," Malani says.

Likewise, most flu patients won't need to see a doctor. Those who are coughing up blood, have trouble breathing or experience a very high fever should seek medical care, as should people with compromised immune systems and those who don't get better after a few days.

How long does norovirus last?

Although norovirus infections come on fast, they also resolve quickly.

"Within 24 to 48 hours you're feeling better, if not close to normal," says Malani, who urges all affected people, especially food service and health care workers, to stay home during that time.

There is no specific medical treatment for norovirus. Patients' symptoms typically improve after three days. Vomiting and diarrhea can cause dehydration, so it's important to consume water or sports drinks to replenish lost fluids.

The flu, which might not surface for two or more days after initial exposure, also has no medical cure. Compared with that of norovirus, recovery time also lasts longer. For some patients, it might be five days or longer before signs of improvement begin.

Flu patients also will benefit from fluids and rest. Cough drops and an alternating regimen of acetaminophen and ibuprofen can help, Malani says. Antiviral therapy is prescribed in certain clinical circumstances.

How to prevent noroviruses

The most important preventive measure? Frequent and proper hand-washing, especially after using the bathroom or before preparing or consuming food. Alcohol-based hand rubs will not kill norovirus germs.

Gymgoers should wipe down all weights and machines with disinfectant wipes. ("Other people will still go to the gym if they're sick," Malani says.)

SEE ALSO: Getting a Flu Shot Can Help Protect Your Heart, Too

And a thorough sterilization at home during and after a norovirus infection is key.

"Take time to clean everything as much as possible," Malani says. Wash sheets in hot water, and wipe down bathroom and high-traffic surfaces — doorknobs, remote controls, light switches and the like — with a bleach-based cleaner.

Good hand hygiene can help keep the flu from spreading, as can covering your mouth when you cough or sneeze.

Just as crucial: getting a flu shot, which helps protect both the recipient and vulnerable populations. "A vaccine might not prevent all flu, but it tends to make the illness less severe," Malani says.