The stew of illnesses swirling through the population right now has many of us sick, sometimes for weeks, but unsure what, exactly, we have.

If you’re having symptoms, how can you tell which virus or infection you have? Because flu, Covid, and respiratory syncytial virus, or RSV, have virtually indistinguishable symptoms, doctors say, it’s almost impossible to know without a test.

It may not matter which flavor of seasonal virus you’ve got. Unless you’re severely ill or are in a high-risk group for severe illness or hospitalization, doctors’ advice is largely the same: stay home and rest until you’re feeling better.

That said, drug treatments for flu and Covid should be started early on, so getting a jump on treatment is important if you think you’ll need it. And strep throat is a bacterial infection that requires antibiotics.

Doctors say there are symptoms that are more associated with some winter illnesses than others.


RSV typically presents as a minor cold in healthy adults and children, most of whom have had the virus multiple times. In the elderly and in babies, RSV can cause more severe illness, including difficulty breathing. A surge in RSV infections hit earlier this year and put pressure on children’s hospitals. National RSV hospitalizations appear to be declining now.

Patients with RSV often display a lot of congestion and mucus secretions, says Preeti Parikh, a pediatrician in New York. Body aches and gastrointestinal distress are less common with RSV. Wheezing, particularly in babies, can occur when the small airways in the lung become inflamed.

Flu vs. Covid-19

Fever, body aches and headaches are more typical of flu and Covid-19, says Dr. Parikh. Gastrointestinal symptoms can also occur with flu, Covid and strep.

Fatigue is more common with flu and Covid-19, says Kristin Englund, an infectious-disease physician at Cleveland Clinic.

Coughing can be a symptom of all three respiratory viruses. A loss of sense of smell and taste is more commonly associated with Covid-19, although doctors say it can occur with other respiratory infections.

How quickly and how severely you first feel symptoms can be one clue in distinguishing among flu, RSV and Covid, says Daniel Kuritzkes, chief of the division of infectious diseases at Brigham and Women’s Hospital in Boston.

With flu, “symptom onset is quite sudden, where people feel like they’ve been hit by a truck or a ton of bricks," says Dr. Kuritzkes. Covid and RSV can hit more gradually, he says.

“If somebody had sudden onset of symptoms and tested negative for Covid, then I would presume that they had influenza, especially now that RSV numbers are dropping off," says Dr. Kuritzkes.

Getting the flu can increase the risk of getting a second infection, including strep throat.

Strep throat

Sore throats are also common in all the viruses as well as strep throat. With strep, the sore throat is often more severe and you may feel difficulty swallowing. If you have a sore throat accompanied by fever, and you’re testing negative for Covid-19, go to a doctor to get tested for strep.

Coughing is less common with strep throat. Other strep symptoms include headache, abdominal pain, a high fever and a diffuse, red rash.

Telltale signs of strep include swollen glands in the neck and red, inflamed tonsils, “which is not what you see in the case of somebody who has a viral infection," says Dr. Kuritzkes.

White patches are often visible in the back of the throat, says Graham Snyder, medical director of infection prevention and hospital epidemiology at the University of Pittsburgh Medical Center.

“For throat infections, seeing your doctor may be important especially if it’s not something that’s resolving after a couple of days," says Dr. Snyder. Viral infections typically begin to get better after a few days, he notes.

Bacteria called group A streptococcus, or group A strep, are common and can cause a range of diseases including strep throat. Most infections are mild and can be treated with antibiotics. However, health officials said recently they are exploring a possible increase in rarer, more serious strep A bacterial infections among children, which occur when bacteria enters the bloodstream.

Common cold

The common cold, or rhinovirus, is circulating, too. If you have upper respiratory symptoms, like congestion and a runny nose, you could have a cold, says Dr. Parikh. Fevers are less common and typically low-grade.

Test and treat

If you’re in a high-risk group for flu or Covid-19, getting tested early is important because antiviral medications must be started early, notes Dr. Kuritzkes. Most healthcare providers can do a rapid test for flu.

When you’re sick, be on the alert for signs of secondary bacterial infections like pneumonia or sinusitis, doctors say, which can sometimes develop in the wake of a virus. Those signs can include a worsening cough that brings up a lot of phlegm, sinus pain, and thick yellow or green discharge from your nose, says Dr. Kuritzkes.

And always call your doctor or seek medical care if you’re having difficulty breathing, can’t eat or drink, or have worsening symptoms.

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