There is a COVID case in your house. What do you do?

With COVID-19 persisting at high levels in the U.S. and millions of Americans retreating indoors during the colder fall and winter months, knowing what to do if the virus enters your house is of paramount importance, experts say.

You may be taking care of yourself or loved ones and simultaneously trying to protect those around you. But how do you do that, especially for those living in close quarters?

And what are the recommendations for vaccinated people, who while more protected from the virus are still susceptible to breakthrough infections?

Experts say that it is critical to isolate those with the virus in the home because of the risk to others with whom they live.

“Data does support the fact that household contacts are at higher risk,” said ABC News’ chief medical correspondent, Dr. Jennifer Ashton.

Any adult or child with COVID-19 symptoms, such as fever, cough, or shortness of breath, should get tested with either a rapid test or a PCR test.

If the test is positive, here are six things to know about trying to stay safe in a shared space.

1. Create as much space as possible

Although it might be difficult to maintain space between family members there are steps that people can take to minimize the risk as much as possible.

“In a perfect world, [the person with COVID-19] would have their own bedroom, bathroom,” says Dr. Simone Wildes, an infectious diseases doctor at South Shore Health.

But if that’s not feasible, then the infected person should “isolate themselves as much as possible." The goal is to limit contact as much as possible between people in the house and to avoid sharing items, wash hands often and keep high-touch surfaces clean.

2. Increase the ventilation in the home

Ventilation is another key component to reducing risk.

“If possible, you want to increase ventilation in the house or apartment,” Ashton said. Weather permitting, you should keep the windows open if possible.

With the temperature in some states already dropping, even a crack in the window would help, said Wildes.

The Centers for Disease Control and Prevention (CDC) recommends filtering the air in your home either through a central system by setting the fan position to "on" or considering using a portable high-efficiency particulate air cleaner. The CDC also recommends pointing fans outside to exhaust virus particles.

3. Everyone who can should mask up

According to the CDC, every person who is capable should be wearing a mask as well, especially the person who tested positive.

Individuals who test positive, even children, are “actively infectious and they can transmit this infection with just simple breathing and talking” according to Ashton. The CDC considers someone infectious for 10 days from when symptoms started and at least 24 hours of no fevers without the use of fever-reducing medications such as acetaminophen or ibuprofen.

The CDC recommends masks that have two or more layers of breathable fabric, completely cover your nose and mouth, fit well against your face and have a wire across the nose that prevents air from leaking out of the top. Masks for children should fit properly and not be used on those who are under 2 years old. There are other exceptions for some people with disabilities.

4. If possible, designate one person as the caretaker

With any sick person, but especially a sick child, they will need some help to get through this disease.

In a two-parent or guardian household, Wildes suggests that one of the parents or guardians should be designated as the caretaker to limit exposure as much as possible. Ideally, this person should be vaccinated. This involves providing over-the-counter medications for symptom relief in addition to making sure they are taking in plenty of fluids.

When caring for someone sick with COVID-19, it is important to watch for emergency warning signs of the illness getting worse. These include trouble breathing, new confusion, unable to stay awake or wake up from sleep, or a change in color to pale, gray or blue colored lips, fingernails or skin.

5. When to quarantine

With any exposure comes the question of quarantine -- separating yourself from the population if you may have been exposed to the virus. According to experts, it will depend on vaccination status.

“I think the most important thing is vaccination status,” said Wildes. If you are vaccinated “you would not need to quarantine, but watch for symptoms.”

If someone in your house is sick with COVID-19, the last exposure would be the day they were no longer considered infectious and no longer isolated. For fully vaccinated people, the CDC recommends getting tested five to seven days after your last exposure even if asymptomatic.

For the unvaccinated, the CDC recommends they quarantine for 10 days after last without testing or symptoms, or seven days with a negative COVID-19 test and no symptoms.

6. Get vaccinated

Ultimately, the best steps one can take to prevent further infections inside a household is to make sure all eligible members are vaccinated.

“Vaccination is still the best way to protect ourselves and those around us,” Ashton said. According to the CDC, unvaccinated people are six times more likely to test positive and more than 11 times more likely to die than the vaccinated.

Jacob S. Warner, an internal medicine resident at Dartmouth-Hitchcock Medical Center, is a contributor to the ABC News Medical Unit.