How Can I Tell Whether I Have Flu or COVID-19?

checking for flu and coronavirus — Dr. Volker Eissing peers into the throat of a patient while checking for flu and also to take a throat swab sample for coronavirus testing at his temporary office in Papenburg, Germany. David Hecker/Getty Images

There's significant potential for a 2020 "twindemic" as flu season looms and the COVID-19 pandemic continues. So, this fall and winter when you feel those sniffles and a scratchy throat start to come on it's going to be only natural to wonder what ails you: influenza or COVID-19? Not to mention, what do you do about it?

The distinction is important, because although both are highly contagious respiratory diseases that are potentially dangerous, they are handled differently. A positive COVID-19 test requires a person to isolate at home for 10 days after the test was initially taken or onset of symptoms, according to the Centers for Disease Control and Prevention (CDC). (People with severe COVID-19 cases or who are immunocompromised may have to isolate even longer, up to 20 days, depending on their doctors' advice.) This is a significant difference from influenza, where people can go back out in public once they've been fever-free without the use of fever-reducing medication for 24 hours. This can obviously affect when a person is cleared to return to work, school or sports.

The mortality rates for both diseases are very different too. For COVID-19, it is 3-4 percent, while for seasonal influenza, the rate is less than 0.1 percent, according to the World Health Organization, which notes that 80 percent of COVID-19 cases are mild or asymptomatic.

What's the Same and What's Different About COVID-19 and Flu Symptoms?

"There is a lot of overlap. There's no one symptom that can definitively tell you have one or another," explains Dr. Ben Singer, pulmonary and critical care specialist at Northwestern Memorial Hospital in Chicago.

For example, all the following are typical symptoms of both flu and COVID-19:

Fever
Cough
Shortness of breath (more severe in COVID-19 patients)
Fatigue
Sore throat
Muscle aches
Headache

These are COVID-specific symptoms:

Loss of smell or taste
Diarrhea
Sometimes, "COVID Toe", purplish spots or rashes that show up on the toes, heels or fingers

Onset and Duration of Flu and COVD-19

One differentiating factor between flu and COVID-19 is how quickly and severely the diseases hit a patient. "Flu people tend to get sick very quickly," Dr. Singer says, noting that by comparison people with COVID get sick over time. "They have symptoms a week or so before they need to come into the ICU."

Typically, flu symptoms develop one to four days after infection, while for COVID-19, it is usually five days after infection, according to the CDC. However, COVID-19 symptoms can begin as early as two days after infection or as late as two weeks after infection. Both flu and COVID-19 are spread from close contact with another person, through coughing, sneezing or talking.

People with full-on flu also tend to get better faster than those patients with serious COVID-19, although people with mild versions of both illnesses tend to recover at around the same rate.

What to Do When Symptoms Present

Here's what you should do when potential COVID-19 or flu symptoms pop up.

Call Your Doctor. You'll be screened over the phone for symptoms and might even have a video conference to determine next steps. "If they don't have the COVID test they almost certainly should know [where to get it]," Singer says. Wondering why you should bother the doctor if they're just going to send you somewhere else for a test? "The doctor knows so much more about people's medical history and whether they would be more susceptible to complications from one disease or another," explains Singer.
Get a COVID-19 Test. If you have symptoms and are so advised by a doctor, get a COVID-19 test. The problem is that the results could take a while to come back. "This is why I would really hope there will be widespread availability of rapid testing for both viruses so when someone has these nonspecific symptoms they could rapidly find out if it's flu, COVID or neither," Singer says. While you wait for results, however, you'll have to isolate at home. At least you're already in conversations with your doctor, in case you get sicker.
Get a Flu Test. Your doctor may also advise you to go ahead with a flu test. In the past, many people didn't bother with this because they could recover at home with little to no intervention. However, a very low percentage of people can have both flu and COVID-19, leaving them extra-vulnerable to complications, and also to making others sick.
Stay Home. Treatment for mild cases is similar for both illnesses. "If you have a mild disease, stay home, rest, drink lots of fluids, treat your symptoms, and keep in touch with your health care provider," says Dr. Leann Poston with Invigor Medical. "In both influenza and COVID, if you have more severe symptoms contact a health care provider immediately." Over-the-counter medications, like acetaminophen (Tylenol), can be used to treat mild cases of COVID-19 or flu. For more severe cases of flu, antiviral drugs (like Tamiflu) are available. Severe cases of COVID-19 may require hospitalization and a variety of other treatments.

Get a Flu Shot to Prevent Confusion

The flu vaccine gets a lot of flack for not being 100 percent effective, but it's still the best line of defense against the illness, as it significantly reduces the severity of the virus if you still manage to come down with it. During a pandemic where mixed messages seem to abound, the health professionals are totally in sync that everyone who's able should get a flu vaccine.

"Only around 2/5 [40 percent] of the U.S. population gets their annual influenza vaccine. If we could double that percentage, we could reach herd immunity and nearly eliminate the presence of influenza in most years," explains Troy Tassier, an associate professor of economics at Fordham University and the author of "The Economics of Epidemiology" in an email. "This is especially important this year with the expected drain on health care resources from a predicted COVID-19 second wave." Indeed, a simultaneous wave of both influenza and COVID-19 could be catastrophic to the health care system.

Dr. Manisha Singal, chief medical officer and critical care physician at Washington, D.C.'s Bridgepoint Hospital cautions people to take the incoming flu season seriously. "There is real potential devastation that co-infection may have on our lives," she says. "Our best defense is a strong offense – we need to utilize the tools and preventative strategies we have available to us now."

Now That's Important

Don't forget about the common cold, which also shares symptoms with COVID-19. Schools and offices are likely to adopt stricter rules about whether people can come in with even mild respiratory symptoms this winter. "It's my hope that the institution of physical distancing measures and masking in schools are going to help prevent a lot of this spread," Singer says, noting that the common cold, influenza and COVID-19 are spread the same way. "So, if you're doing things to block transmission of COVID you're doing things to block the others."