The only way to know for sure is to find out if the infection is viral or bacterial.
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But that's something that's currently not easy to do in a doctor's office.
That's why a Duke doctor and his team are developing a rapid test that could end the dilemma and the over-prescribing of antibiotics.
If you have common cold or the flu caused by a virus, over-the-counter medications are often all that's needed.
However if your infection is bacterial, your doctor may want to prescribe antibiotics.
"Respiratory infections are the most common reason that people go and seek care from a health care provider. And that's always one of the questions that the doctors need to try and sort out is do I need to give antibiotics or not," said Duke researcher and medical doctor Ephraim Tsalik.
Tsalik says doctors don't have tests available to quickly answer that question in their office.
And it's an important question since the over-use of antibiotics is creating resistant strains of bacteria.
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"The situation has gotten better over the course of the past several years, but there's still a lot of inappropriate use, simply because those tools are missing," Tsalik said. "So there's a great need for tests like the ones that we've developed."
His test uses a small kit in a plastic pouch about the size of a smartphone to measure the changes in gene activity and tell a doctor whether a patient has a bacterial or viral infection.
There are a few things that are novel about the test kit.
For one, it's fast.
After a small amount of blood is added to the plastic pouch, the pouch is inserted into a machine about the size of a small computer printer.
And it spits out results of the test in under an hour.
Dr. Tsalik and his team hope to make it even more rapid as they continue to refine the process.
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He also hopes to make it affordable so there can be a machine in every family practice.
Another novelty, it doesn't look for the specific cause of the infection.
Instead, it examines the patient's immune response.
"We're actually looking at changes at the genetic level that indicate whether the immune system is responding to a virus or a bacteria," Tsalik said.
Dr. Tsalik and his colleagues have published a study on their research in the Journal of Critical Care Medicine that shows the tests are more effective than current pathogen testing.
And the technology behind the rapid test could have other important uses down the road.
"The pipeline that we're developing will really open up opportunities for a variety of other disease applications. So...I think it holds a lot of promise beyond just this one question," Dr. Tsalik said.
He hopes to bring the rapid test kit to market in the next two years.