(NewsNation) — With respiratory illness spiking across the country, there’s a good chance you’re sick to start the new year.

Maybe you have the symptoms of COVID-19, prompting you to take a test or two that you received for free from the federal government in 2023. It’s also possible you’re testing negative.

While there is a relatively obvious reason why your test is negative (more on that in a moment), there is another less obvious possibility you may be overlooking.

You may recall hearing that some of the COVID tests shipped out by the government in October were already beyond their printed best-by date. Some of those tests had expiration dates for February 2023, a whole eight months before they arrived in mailboxes.

However, the Food and Drug Administration said the tests were not actually expired, noting that it had extended the expiration dates for more than a dozen at-home COVID test kits. So the aforementioned kits that were originally set to expire in February 2023 were instead listed as being effective until February 2024.

As you may have guessed, COVID tests aren’t considered effective beyond their extended expiration dates. That means if you’re testing negative, it could be that your test is out of date. The FDA previously warned that expired COVID tests shouldn’t be used because the parts they are made of may “degrade, or break down, over time” and give “inaccurate or invalid test results.”

Tests you may have in your bathroom cabinet, like the iHealth COVID-19 Antigen Rapid Test or the BinaxNOW, are among those with extended expiration dates. For iHealth kits with printed expiration dates ranging from February 2023 to September 2023, the extended dates have since passed. BinaxNOW kits with printed dates prior to June 2023 have also passed their extended expiration dates.

You can find the full list of COVID tests with extended expiration dates on the FDA’s website.

If your test kit has not expired, and you’re still testing negative, you may just have a different respiratory illness.

“If you are feeling symptomatic and you test negative for COVID-19, usually the most likely reason is you’re infected with something else besides COVID-19,” said Dr. Andrew Pekosz, a virologist and professor at Johns Hopkins Bloomberg School of Public Health, during a media briefing.

After all, two other respiratory viruses, influenza and RSV, are starting to circulate at high levels in many states, and all three illnesses have overlapping symptoms.

But Pekosz went on to say that a negative test doesn’t really change much as far as next steps go.

“If you’re feeling sick, there really should be no difference whether you’re testing positive for COVID-19, flu or RSV,” he said. “If you’re feeling sick, stay home, take care of yourself. If you’re in a high-risk group, seek medical attention so you can get some advice as to what to do. There are a lot of viruses out there that are causing similar spectrums of diseases. So if you’re feeling sick, you are sick.”

The CDC also notes that a negative COVID test doesn’t entirely mean you’re free of infection. Even if the virus is not detected, it could still be there in small amounts. The CDC went on to say that you may have another illness you need to get tested for, and that you should consult your health care provider if you have questions about test results or your symptoms.

Jeremy Tanner contributed to this report.