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How do I know if my symptoms are from Covid, the common cold, flu or R.S.V.?

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Sept. 22, 2022, 2:36 p.m. ET

The flu, Covid and respiratory syncytial virus (R.S.V.) have symptoms that overlap — and also can look quite similar to those of the common cold, which is caused by a variety of viruses. You can develop a cough, fever, headache or runny or stuffy nose with any respiratory virus, said Dr. Michael Chang, an infectious disease specialist at Memorial Hermann Health System in Houston.

One way to differentiate among viral infections is to monitor how quickly your symptoms ramp up. Symptoms of the flu come on quickly — often just one day after exposure to someone who was sick — and can be felt all over the body. People with the flu often describe feeling like they’ve been hit by a truck, Dr. Chang said. With colds, symptoms may take two or three days to appear and are much milder.

Covid and R.S.V. have even longer incubation periods. It can take an average of five days from exposure to the coronavirus to the development of early Covid-19 symptoms, though newer subvariants like BQ.1 and BQ.1.1 may result in an active infection as soon as three days after exposure. R.S.V. takes about four to six days. With Covid and R.S.V., symptoms also build slowly: You may start out feeling sniffly, then develop a cough or a headache the next day and a fever the next.

Adults afflicted with the flu are likely to experience very high fevers, up to 103 or 104 degrees, Dr. Chang said. But fevers rarely accompany colds, particularly in adults. People with Covid-19 and R.S.V. experience mild fevers or none at all. “Especially with the newer variants and people having been exposed through immunization or if they’ve had an infection before, we’re seeing that more patients are now only mildly symptomatic, and they only have low-grade fevers, around 99 or 100,” Dr. Chang said.

A few symptoms are unique to Covid, such as brain fog, which occurs most frequently in older adults. Some people with Covid lose their sense of taste and smell, while others occasionally experience rashes and blisters on their toes or a sudden onset of hair loss.

People with R.S.V. are unlikely to feel muscle aches and fatigue. Instead, R.S.V. is often accompanied by a distinctive wet and forceful cough. Young children with R.S.V. may also produce a high-pitched wheezing sound when they exhale.

Compared to adults, young children experience more severe symptoms of R.S.V. and the flu — but kids seem to have more asymptomatic or mild bouts of Covid-19. People over the age of 65, those with underlying medical conditions and pregnant women can experience severe illness with all three viruses.

The only reliable way to tell which infection you have is by testing, said Dr. Adam Ratner, a pediatric infectious disease specialist at N.Y.U. Langone. An at-home Covid test can quickly determine whether or not you have the virus, although testing too soon after infection can lead to false negatives. Experts advise taking a second rapid test 24 to 48 hours after the first, to ensure the results are accurate.

You can also try a combined P.C.R. test developed by Labcorp that allows you to take a nasal swab for Covid-19, flu and R.S.V. and mail the sample to a lab. Results take one or two days. Most clinics, urgent care centers and hospitals also offer combination tests for all three viruses.

We’ve also created this interactive guide to help — you can mark symptoms and then sort by selecting an illness below.

Rarely

•• Sometimes

••• Often

*A stuffy nose may temporarily decrease the ability to taste or smell but it does not cause a sudden, complete loss of these senses.

Source: Centers for Disease Control and Prevention

Dani Blum is an associate reporter for Well at The Times. More about Dani Blum

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