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Are that sore throat and cough signs of the flu, the coronavirus or something else?

Most cases are likely to be mild, but all three viruses are capable of causing more severe illness than the ubiquitous common cold. “I think the big difference for 2022 is there’s a higher chance that the thing you have, that might be a cold, might cause somebody else to be seriously ill,” said UCSF infectious disease specialist Dr. Peter Chin-Hong.

So, if you develop symptoms of a respiratory illness, how can you figure out what you have? And what should you do once you know?

How can you tell if it’s flu, RSV or COVID?

Symptoms alone probably won’t be enough to answer the first question, health experts said.

There is “tremendous overlap” in symptoms of COVID, flu and other respiratory viruses including colds, said Dr. Dean Winslow, professor of medicine at Stanford University. There’s also evidence that
symptoms of COVID are evolving
and can vary in people depending on their vaccination status and any previous infection.

“People who were very sick (with COVID) early in the outbreak before vaccination was available often presented much more with high fever and shortness of breath,” Winslow said.

“Most people we’re seeing now — at least who have normal immune systems, have been vaccinated and/or have had prior infection — are presenting more with upper respiratory symptoms, with runny nose, sore throat and cough. Which are very similar to the symptoms people have with rhinovirus or other upper respiratory viral infections.”

Flu symptoms can include fever, cough, body aches and congestion and typically arise suddenly after infection, according to the Centers for Disease Control and Prevention. COVID-19 shares a number of common symptoms with the flu, and testing is needed to diagnose the specific virus, the CDC states.

RSV typically causes mild, cold-like symptoms — like runny nose, coughing or wheezing — from which most people will recover quickly. In infants under 6 months old, the only symptoms of RSV might be irritability, decreased activity and appetite and pauses in breathing, per the CDC.

But RSV can also lead to more severe infections like bronchiolitis or pneumonia, with such outcomes more likely in infants and older adults.

How and why to get a diagnosis

If symptoms arise that might be COVID, taking an at-home antigen test is a good idea, health experts said.

While a positive result can provide some clarity — false positives are rare — one negative result is not a reason to rule out COVID entirely, said John Swartzberg, an infectious disease expert at UC Berkeley.

“We’re seeing quite a few people early in the course of omicron who test negative initially and then when they repeat it in 24 to 48 hours it’s often positive,” Swartzberg said.

Several experts suggested following up a negative at-home test with a second test 24 to 48 hours later; if that’s also negative, you probably don’t have COVID.

For people with underlying health issues or who are at higher risk for severe illness, getting tested promptly can accelerate access to treatments aimed specifically at the virus they have.

For instance, antiviral drugs for influenza, such as Tamiflu, work best within 36 hours of the onset of illness, said Chin-Hong. And among higher-risk patients with COVID-19, the
antiviral drug Paxlovid
is found to significantly reduce risk of hospitalization and death and should be started within the first five days of symptom onset.

Other factors that might prompt getting a diagnosis include living with others who are more at-risk for serious illness — such as older adults, infants or people who are immunocompromised — and the extent of one’s own symptoms, Swartzberg said.

“If you wake up with the sniffles or you’ve got a sore throat or a little bit of a cough, it’s probably not terribly important if you’re otherwise healthy,” Swartzberg said. “If you’re sick with a fever and body aches and coughing, feeling a little short of breath and it’s getting worse, no matter how healthy you are, I would seek medical care, or at least medical advice.”

What if your COVID test is positive?

Federal and state health officials both lay out guidance for what to do following a positive COVID test.

“I think a prudent approach to take … if your rapid antigen test for COVID-19 is positive, is to stay home for five days and avoid family members, particularly those who may be susceptible to more serious complications,” said Winslow.

Anyone who tests positive, regardless of vaccination status, should isolate at home, per the CDC, which advises wearing a high-quality mask if you must be around others.

Those with no symptoms, or who have improving symptoms and are fever-free for 24 hours without use of medication, can end isolation after five days. They should continue wearing a mask through day 10, or until returning two sequential negative tests 48 hours apart, the CDC guidelines state.

People who experienced shortness of breath are advised to isolate through day 10. Most people recover with home care, such as resting and drinking fluids, but should monitor symptoms and seek medical care if they get worse, according to the California Department of Health.

“A lot of people can’t afford not to take care of family members,” said Chin-Hong. “So, washing hands, wearing a mask and paying attention to ventilation, for COVID particularly, is important.”

As for medication, recent research suggests it’s fine not only to take pain relievers like acetaminophen but also cold products such as decongestants or cough syrup as needed to relieve symptoms, just as you would for the flu.

What about children and RSV?

Pediatric hospitals across the U.S., including in the Bay Area, are
seeing a rush of respiratory virus cases
driven by an RSV surge.

Most children will get RSV by age 2, with mild cases. But RSV also causes up to 80,000 hospitalizations and 300 deaths each year among children under 5, according to the CDC, and is the foremost cause of pneumonia in children under age 1 in the U.S.

Signs of a possibly more severe case, especially in babies, include trouble with breathing or feeding and staying hydrated, the latter often evident by fewer wet diapers, said Dr. Alan Schroeder, associate chief for research of pediatric hospital medicine at Stanford Medicine Children’s Health.

“If you notice your child is struggling to breathe, if they’re (breathing) faster or using the muscles below or above the ribs to help them breathe, that would warrant prompt medical attention,” Schroeder said.

Such issues are less common in older children, who typically experience RSV as cold symptoms, said Dr. Nelson Branco of Tamalpais Pediatrics in Marin County.

How should you navigate feeling sick from a social and public health standpoint?

Say you feel under the weather tomorrow. You take a rapid COVID test and it’s negative. What should you do then? Take extra precautions? Alert others, even if it’s just a case of then sniffles?

“My sense is if you have a fever and you’re feeling bad, you should of course stay home,” said Winslow, of Stanford. “If you have only mild symptoms, it might be reasonable to go ahead and go to work. But I think as a courtesy to your coworkers and your family, at least when you’re in an indoor environment, I think it’s prudent to consider wearing a mask.”

Wearing a mask “pretty significantly” reduces the release of small particle aerosols and large droplets, two major ways that respiratory viruses are transmitted, Winslow said.

“So to me, it’s almost an ethical, moral issue, in that wearing a mask indoors, even if you have relatively mild symptoms, shows respect and concern for your fellow citizens,” he said.

As for being out in public: “If you’re going into your local Safeway store, I certainly wouldn’t feel obligated to share with everyone that I was having some mild sniffles that day,” said Winslow. “But if you work in a small office … you might want to at least share with them why you’re wearing a mask.”

Swartzberg, of UC Berkeley, said he thinks “we live in a different world now” since the arrival of COVID-19 and “we need to take care of ourselves, but we also need to take care of our communities.”

“If your job can’t be done from home and you have to be there because you have to put food on your table and pay rent, wear a mask when you’re out to decrease chances of your transmitting anything,” Swartzberg said. “Pay more attention to your hand hygiene than you did before COVID, not because COVID is primarily spread by the hands, but we know some respiratory viruses are.”

As pandemic restrictions ease, people are left to weigh risk and mitigation. A recent study published in JAMA Network Open, for example, found that more than 40% of U.S. adult participants had
lied about their own health
or skirted COVID-related public health measures.

Health experts urged getting the COVID-19 bivalent booster and a
flu shot
to fortify immune defenses. There’s no vaccine for RSV. It’s unclear how the viruses might interact with each other this winter after the last two winters saw unusually low levels of flu, RSV and other respiratory illness.

“There’s nothing stopping you from getting multiple viruses at the same time,” said Chin-Hong. “But we haven’t seen that too commonly, even in the last few years when we have multiple viruses circulating.”

Matt Kawahara is a San Francisco Chronicle staff writer. Email: Twitter: @matthewkawahara