We're entering that time of the year when there are multiple communicable diseases in play, and the similarities between them will make it hard to distinguish which one you're experiencing.

Typical symptoms of the flu, Covid and the common cold all include coughing, sore throat and a runny nose. And because of that overlap, testing is the only way to be sure, according to Céline Gounder, an infectious disease specialist, epidemiologist and senior fellow at the Kaiser Family Foundation.

"At this stage in the pandemic, it's really difficult to differentiate between the flu, Covid, common colds and even seasonal allergies," says Gounder. 

"I, even as an infectious disease specialist who's been practicing for a couple decades now, cannot differentiate just on an exam. You really need to do a test."

Early in the pandemic, symptoms like red eyes and loss of smell and taste were clear indicators of Covid-19, but those distinctive indicators aren't showing up in most people with the disease anymore, she adds.

"That's probably a reflection of two things: one, most people have some degree of immunity, so it's playing out a bit differently when people get infected. Secondly, the virus has mutated and different variants are going to behave differently," Gounder says.

Is It a Cold, the Flu or COVID-19?

Source: Centers for Disease Control and Prevention
Credit: Andrew Williams / NBC; Gabriel Cortes / CNBC

Steps to take as we enter cold and flu season

"Wearing a high-quality mask, whether it's a KN95 mask or an N95 mask, when you're indoors in public places, will certainly reduce your risk," says Gounder.

She also recommends:

• Getting vaccinated against Covid-19, including the updated omicron-specific booster
• A seasonal flu shot, which the CDC recommends for everyone six months of age and older

To avoid putting others at risk and to help minimize the severity of any illness you might contract, you should stock up on at-home antigen tests for Covid-19, Gounder suggests.

And if you do end up feeling under the weather, it would be best to assume you may have Covid, and act accordingly by testing and isolating yourself from others.

Even if you test negative on the first day, Gounder recommends retesting on day two to be sure. "If by two days after developing symptoms you're still not testing positive on those at-home tests, it's pretty unlikely you have Covid."

Ideally, people should get diagnosed with viruses like Covid-19 and the flu early in the course of illness, Gounder says.

Detecting those conditions in their beginning stages allows people to receive treatments like Paxlovid for Covid and Tamiflu for influenza to prevent serious complications down the line like hospitalization, she adds.

If you're experiencing severe symptoms like a drop in your oxygen levels or shortness of breath, she strongly recommends going to the hospital where you will be able to receive medical attention and additional testing. 

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