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Is it Covid, flu or RSV? A few hallmarks can help distinguish between the illnesses

NBC News 11/24/2022 Aria Bendix and Nigel Chiwaya
© Provided by NBC News

Covid, flu and respiratory syncytial virus (RSV) are together driving a national wave of respiratory illnesses.

Around 76% of U.S. hospital inpatient beds are full, according to data from the Department of Health and Human Services. Pediatric beds are at a similar level, though six states have 90% or more of their pediatric beds full, according to an NBC News analysis of HHS data.

Covid, flu and RSV can be difficult to distinguish, since they share many common symptoms. But it's useful to know which virus you have, since that determines the treatments you should receive and how long you should isolate.

Certain hallmarks — either symptoms or how the illness progresses — can help differentiate each virus. Here are five factors to consider.

Some symptoms are unique to particular viruses

A runny nose, cough, congestion or sore throat can arise because of any of the three viruses or a common cold. But a loss of taste and smell is more commonly associated with Covid than with flu or RSV. And wheezing is often a tell-tale sign of a serious RSV infection, usually found in kids or older adults.

The only way to know for certain, though, is to get tested.

“I don’t think anybody would ever go, ‘Hey, listen, I think you have a virus based on your symptoms,’ and feel confident to say what virus that is,” said Dr. Frank Esper, a pediatric infectious disease specialist at Cleveland Clinic.

Are symptoms coming on gradually or all of a sudden?

Flu symptoms tend to develop more suddenly than those of Covid or RSV.

“Flu classically comes on with an abrupt fever first that happens pretty quickly. That’s somewhat contrasted by RSV and Covid, where we think of a slow escalation in symptoms,” said Dr. Scott Roberts, a Yale Medicine infectious disease specialist.

How long has it been since exposure?

The illnesses have different incubation periods — the time between exposure and symptoms. On average, flu symptoms tend to develop two days after exposure to the virus, whereas RSV symptoms tend to take around four to six days to appear, and Covid's typical incubation is three to four days for the omicron variant.

"If I go to a party and I get symptoms the next day, it’s probably flu because that can be as short as 24 hours’ incubation period," Roberts said.

Age makes a big difference in a disease's symptoms and severity

RSV is unlikely to make a healthy adult feel very sick, whereas Covid and flu certainly can.

“In general, if you’re a young healthy adult or you’re not in an extreme of age, and you get pretty severe illness, it’s probably not RSV,” Roberts said.

The groups most vulnerable to severe RSV infections are babies, children with lung diseases, adults ages 65 and up and people with weakened immune systems.

Symptoms can also look different depending on your age and immune status. Many kids are encountering respiratory viruses for the first time this year as they return to regular schooling and socializing, so their bodies may have a harder time clearing the infection, which can lead to more wide-ranging symptoms.

According to Esper, almost a fourth of children have gastrointestinal symptoms (like diarrhea, stomach pain or vomiting) from viral infections. That's less common in adults with seasonal flu or RSV.

People with weakened immune systems, meanwhile, are more likely to develop severe symptoms or pneumonia from any of the three viruses.

Consider which virus is circulating the most in your community

Disease experts anticipate that Covid cases will climb over the holidays as more people travel and gather indoors. Average daily cases reported to the Centers for Disease Control and Prevention have already risen nearly 11% over the last two weeks, according to NBC News’ tally.

But it's difficult to determine local Covid transmission levels, since many people use at-home tests. RSV and flu tests, by contrast, are performed at a doctor’s office or ordered via prescription.

RSV infections seem to have passed their peak nationally. Although the CDC does not keep a national count of RSV cases, the number of positive weekly tests fell from more than 17,000 in the week ending Nov. 5 to around 9,000 in the week ending on Saturday.

By contrast, flu cases are skyrocketing. The national share of influenza tests that came back positive rose from around 8% in the week ending Oct. 30 to nearly 15% in the week ending Nov. 13. Flu hospitalizations are the highest they've been at this time of year in more than a decade. 

Esper said he expects the Cleveland Clinic to be “swimming in flu” two weeks from now.

The picture varies by region, however. In the Northeast, Roberts said, “we saw RSV surge over the last one to two months and it’s actually plateaued — which is great news — and then flu, only the past few weeks we’re seeing an exponential rise."

“The Southeast U.S. — Georgia, Alabama, Mississippi — they saw kind of the opposite. They saw initially a surge in flu, and then now you’re seeing RSV start to catch up,” he added.

Available treatments and vaccines

Unlike Covid and the flu, there are no vaccines or universally prescribed treatments for RSV.

"RSV scares me the most, probably, because you can’t do anything about it and so many young kids haven’t seen it. We’re really seeing record surges in our pediatric hospitals,” Roberts said.

To reduce the length of flu symptoms, though, doctors usually prescribe Tamiflu or one of three other approved treatments. For some people with Covid, doctors can prescribe Paxlovid.

Dr. Ashish Jha, the White House Covid-19 Response Coordinator, emphasized the benefits of getting flu shots and Covid boosters.

“In this moment where we have a lot of flu, still have a decent amount of RSV, still got a good amount of Covid, the single most important thing people need to do is go get vaccinated,” Jha said at a Tuesday briefing. “It keeps you out of the hospital.”

This article was originally published on NBCNews.com

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