How to differentiate between flu and coronavirus

As influenza season approaches, some Americans, and especially parents, are worried that if they or their children should become ill, it may not be easy to know which disease they have — the flu or Covid-19.

They are correct. Most symptoms of the two diseases are so similar that short of a test — or two or three tests — it won’t be possible to know for sure. But there are some clues. (And it is possible to have both infections at the same time; some patients in China this year were found to have both.)

Read: Fly away flu

But first: Get a flu shot.

It is not yet clear whether the United States will have much of a flu season this year. Flu activity in the Southern Hemisphere, which is often predictive of activity in the US, was 99% below normal during its winter. Epidemiologists believe that is because Australians, New Zealanders, South Africans, Chileans and other residents of the southern half of the globe were wearing masks, staying several feet apart and washing their hands to prevent transmission of the coronavirus. Those same precautions also prevent flu transmission.

Because there are very few flights between the Southern Hemisphere and the US right now, there may be no opportunity for the usual four seasonal influenza strains to “reseed” themselves among Americans. If they do, masks and social distancing should limit their spread.

Also read: When and why you should get a flu shot

Nonetheless, experts urge all Americans to get flu shots. Before it ended abruptly during lockdown, last year’s flu season was on track to be one of the worst in recent memory. The number of children who died was equal to that in the 2017-18 season, which was the worst since the Centers for Disease Control and Prevention began tracking flu-season deaths in 1976.

If you catch the flu, experts say, having had the shot makes it much less likely that you will be hospitalized or die.

Because of the fears of a “twindemic,” flu shots were made in large numbers this year and distributed to pharmacies and doctor’s offices beginning in August, which is early. As of late last month, some doctors reported difficulty ordering as many as they want, but pharmacy chains say they are getting steady supplies. To find a flu shot, try vaccinefinder.org or one of the chain pharmacy websites, such as CVS.com/immunizations/flu.

Assessing the difference between a cold and the flu.

There are at least 100 viruses that can cause the common cold, but only four that cause seasonal flu. Many people who catch colds assume they have the flu, but experts consistently say the same thing about how to tell the difference: “Flu makes you feel as if you were hit by a truck.” The fever, aches and headaches of a bad case of influenza are generally worse than a case of respiratory syncytial virus, rhinovirus or other common cold viruses.

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Everyone knows the symptoms of the flu: fever, headaches, body aches, sore throat, runny nose, stuffed sinuses, coughing and sneezing — and, for infants, ear infections. Some victims, especially children, get diarrhea or vomiting too.

In severe cases, the most common complication is pneumonia. The typical signs of a flu pneumonia are shortness of breath, especially when you exert yourself, and unusually rapid breathing — doctors typically look for that in children — and sometimes pain in the chest or back.

Identifying Covid-19 by its flulike and ‘wacky’ symptoms.

Knowing whether you have Covid-19 is much more complicated because there are so many different — and sometimes pretty wacky — symptoms, many of which echo those of the flu.

The most common symptoms are high fever, sometimes with chills, a dry cough and fatigue.

The one sign that really distinguishes the two infections is that many Covid-19 victims suddenly lose their sense of smell — not because they have a stuffy nose but because they don’t register even strong odors like onions or coffee. Not all virus victims get anosmia, the formal name for loss of smell, but one study found that 87% did.

Less common symptoms include a sore throat, congestion, runny nose, vomiting, diarrhea, stomach pain and feeling somewhat out of breath when exerting yourself. Some victims have red or itchy eyes, and some get redness or blisters on their fingers or toes — so-called Covid toes, which resemble chilblains.

More dangerous symptoms — which mean you should get immediate medical attention — include serious breathing difficulty; pain or pressure in the chest; blue lips or blue face; confusion or incoherent answers to simple questions; and collapsing or losing consciousness.

Adding to the disease’s fearsome nature is that it can cause blood clots that lead to heart damage, brain damage and lung damage. And even some cases that appear mild or asymptomatic create signs of what doctors believe may be long-lasting heart damage.

Another unusual aspect of Covid is that people sometimes develop pneumonia without realizing how sick they are. Doctors are unsure why; one theory is that the air sacs in the lungs are damaged in a way that does not cause the buildup of carbon dioxide, which creates that “desperate for air” feeling.

Many doctors recommend buying a pulse oximeter, a fingertip device that measures oxygen levels in the blood. Multiple readings below 92% should trigger a call to a doctor. The earlier pneumonia is caught, the better the outcome.

Understand that Covid-19 symptoms in children are similar to those in adults.

Children generally get through Covid-19 with few problems; for the youngest ages, it is thought to be less dangerous than the flu.

Children have the same constellation of symptoms that adults do, although parents may be more likely to notice it when their youngsters have runny noses, red eyes and the exhausted crankiness that comes from just feeling terrible.

Dangerous symptoms include difficulty breathing, bluish lips, confusion or inability to wake up, and intense abdominal pains or inability to keep down any liquids. If there are any signs of these, it is important to get a child to a doctor or hospital quickly.

In very rare cases, children can get multisystem inflammatory syndrome, which is thought to be caused by an overactive immune response and can cause shock and organ failure.

But doctors emphasize that it is rare and that parents should realize it is highly unlikely their sick child has it.

Expect potential difficulties with testing.

For Covid-19, symptoms can begin two to 14 days after exposure, but most begin five to seven days after it.

However, as with diseases like measles, you can start spreading the virus two days before you begin to feel sick. So if you think you might have been exposed, it is very important to warn others and isolate yourself from them as soon as you can, especially if they are older or medically fragile.

It is an axiom of general medicine that when one disease is sweeping through an area and a patient has its symptoms, it is usually safe to assume that’s what the patient has and begin treating it, rather than waiting for test results. So unless both the flu and the coronavirus begin circulating heavily at the same time in your city, do not be surprised if your doctor does not recommend a test.

And getting tested for the coronavirus can be tricky, especially with so many test delays. The PCR type is more accurate than 15-minute “rapid antigen tests,” but it can take hours or even days to return results, depending on whether it has to be sent away to a central lab.

One positive test probably means you are infected, but one negative test should not be trusted; too many things can go wrong. Two negative PCR tests taken at least 24 hours apart are a better indication of whether you are infection-free.

If your insurance company will pay for only one test, you might consider paying for the second one yourself for the peace of mind.