Is Your Cold a Virus or Bacterium? How to Tell the Difference

Have you ever had a bad cold or a nagging cough and wondered if it was a virus or bacterial infection? Knowing the difference can save you time and money during cold and flu season.


“The symptoms of a bacterial infection and a virus are often very similar—fever, muscle aches, cough, and sore throat—but they require different treatments,” says Soma Mandal, MD, an internal medicine physician at Summit Medical Group. “People should rely on their general practitioner to distinguish between the two. Most respiratory illnesses are not serious—the culprit is usually a virus.”


Bacteria, which cause ear, strep throat, and sinus infections, as well as bronchitis, pneumonia, and whooping cough, are treated with antibiotics. Viruses, however, which lead to the common cold, the flu, and certain pneumonias, do not respond to antibiotics.


When people take antibiotics unnecessarily it causes resistance, meaning the medication does not work as well when you really need it. Antibiotics can also cause side effects, most commonly upset stomach. According to the Centers for Disease Control and Prevention, 1 in 3 antibiotics prescribed is unnecessary.


“We suspect that a respiratory illness is caused by a bacterium if patients have recurring fevers, symptoms that last more than 10 days, shortness of breath, or excessive yellow or green mucus,” says Dr. Mandal. “I always remind my patients that some green or yellow phlegm can be caused by a virus. Congestion can be uncomfortable, but unless there are other signs of infection, they usually do not need an antibiotic.” 


Unfortunately, viruses are a waiting game, typically lasting 7 to 10 days. Dr. Mandal says over-the-counter nasal sprays and fever reducers like Tylenol or Motrin can help patents feel more comfortable.


Sometimes a virus can weaken your immune system and damage the tissue, making it easier for bacteria to grow. That is why Dr. Mandal recommends patients make an appointment if they are not feeling better after 10 days. People with an increased risk for bacterial infection—such as the elderly or individuals with compromised immune systems—should see a physician within the first few days.



Call to Action: Most respiratory illness is caused by a virus and does not need to be treated by a physician. Make an appointment if you have signs of a bacterial infection including: symptoms that last more than 10 days, recurring fevers, shortness of breath, or excessive yellow or green mucus.





By Carolyn Sayre

Reviewed by Soma Mandal, MD




Last reviewed: December 2016


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