Spring might be right around the corner, but the winter respiratory viruses—including flu, COVID-19, and RSV—are still going strong, according to the Centers for Disease Control and Prevention. 

As of Feb. 19, nine states have “very high” case numbers of respiratory illnesses, and most of the remaining states are in the “high” or “moderate” categories. The flu has been particularly prevalent, with a case positivity rate of 27%, compared to just 16% this time last year.

The CDC says that most people who get sick with a respiratory illness will have mild symptoms like a sore throat and cough and recover after about a week without needing additional medical care. But sometimes symptoms can become more severe, making it difficult to know whether it’s best to try to ride them out or take a trip to the emergency room.

That’s why we asked experts to explain the red-flag signs of a respiratory illness that are serious enough for an ER visit. Here’s what they said.

While symptoms can vary slightly from virus to virus, respiratory illnesses often bring on head cold symptoms like a cough, runny nose, sore throat, or headache, as well as effects such as a fever, chills, body aches, or fatigue.

But if your symptoms take a turn for the worse, it’s important to seek emergency medical care. That’s the case whether you’re battling flu, COVID, RSV—or if you’re unsure what you have.

One thing to pay attention to is whether you’re showing severe signs of dehydration, which can occur if you’re feeling too sick to drink or eat, Benjamin Barlow, MD, a board-certified emergency medicine physician and the chief medical officer at the urgent-care network American Family Care, told Health.

Dark yellow urine, dizziness or lightheadedness, and headaches all signal that you should drink something as soon as possible. But if you faint or start experiencing confusion or an ongoing rapid heartbeat, that means you could be dangerously dehydrated, Barlow stressed, and you might need intravenous fluids. 

Difficulty or rapid breathing could also signify extreme dehydration, Barlow said. Or it could mean that you have pneumonia or low oxygen levels.

“Any time people are feeling short of breath, that’s a major warning sign,” he explained. “When you feel short of breath, you’re breathing harder, and your heart rate is going up. It’s your body telling you you’re getting worse and you need to hydrate or be put on oxygen.”

A bluish tint to your lips and fingers could also indicate low oxygen, Andrea Giamalva, MD, FAAP, a family medicine physician and chief medical officer at Experity, told Health. That would be enough for an ER trip, she added, as would feeling so lethargic that you can barely get out of bed. 

All of these red-flag symptoms apply to kids as well, Barlow noted. It’s extra important to pay close attention to a child’s behavior and appearance because they might not be able to tell you how they’re feeling.

“Are they breathing more heavy? Do their eyes seem a little sunken in? The big difference between adults and kids is we have to be really observant of the kids’ behavior and how they look,” he said. 

For babies under 3 months, a fever of 100.4 degrees or higher warrants a visit to the ER or pediatrician, Tanya Altmann, MD, a pediatrician and author, told Health.

In general, pregnant people and the very young and old have the highest risk of severe illness from a respiratory virus.

“The impact of the disease is far more on younger and elderly patients, and especially on those with many medical conditions,” Michael A. Bernstein, MD, director for pulmonary and critical care at Stamford Health, told Health. “Immunocompromised individuals and those with cardiac and respiratory disease are at the most risk for morbidity and mortality.” 

According to the CDC, older adults account for an estimated 50% to 75% of total flu hospitalizations. In 2023, adults 65 and older made up a majority of COVID-related hospitalizations. And about 100,000 to 150,000 adults in this age group will also be hospitalized each year for RSV.

RSV is particularly worrisome for infants and young children: “It’s the leading cause of respiratory illness hospitalization for kids under 5 in the U.S.,” Altmann said.

Experts agree that one of the best ways to prevent a severe respiratory illness is to get vaccinated—the CDC recommends that most people 6 months and older get an annual flu and COVID shot. An RSV vaccine is available for pregnant people and those over 65, while infants younger than 8 months can receive a shot of monoclonal antibodies. “It’s working really well to keep infants out of the hospital,” said Altmann.

Beyond vaccination, Altmann suggests taking daily precautions to minimize your risk of getting sick. These include washing hands thoroughly with soap, disinfecting surfaces, avoiding crowded indoor areas, and trying not to touch your face with unwashed hands.

If you do get sick, over-the-counter medications like Tylenol and Motrin can help you manage symptoms at home, Barlow said. Those drugs can help you “feel good enough to keep yourself hydrated and put nutrition in your body so you aren’t getting sicker.” 

Your healthcare provider can also prescribe medication to lessen the severity of COVID or the flu, but the key is to act quickly. 

Tamiflu, an antiviral for the flu, is often only prescribed after a positive test, but the medication works best when taken within a couple of days of symptom onset. The window is slightly bigger for COVID: Your provider can prescribe an antiviral medication such as Paxlovid or Lagevrio within five days of your first symptom. 

Unfortunately, there’s no antiviral treatment for RSV, said Giamalva. “But anytime we test and get information as far as what actual virus is causing your illness,” she noted, “we as providers can give a whole lot better kind of trajectory or plan or overall perception of what we expect will come in the next couple days.”