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Living Well

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

Last updated: Nov 28, 2016

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. Soma Mandal, MD, an internal medicine physician at Summit Medical Group, discusses how to tell when you need antibiotics, or simply take a wait-and-see approach.

Q. What are bacteria and viruses?

Dr. Mandal: Bacteria are one-celled organisms that multiply and are linked to ear, throat, and sinus infections, as well as bronchitis, pneumonia, and whooping cough. Viruses are little parasites that reproduce rapidly and cause the common cold, the flu, and certain pneumonias. Most respiratory illnesses are not serious—the culprit is usually a virus not bacterium.  

Q. Bacterial and viral infections feel similar to me. How can you tell the difference?

Dr. Mandal: People should rely on their general practitioner to distinguish between the two. We suspect that a respiratory illness is caused by a bacterium if you develop a secondary fever after the first few days of being sick. Make an appointment if you have:

  • Symptoms that last more than 10 days
  • Recurring fevers
  • Shortness of breath
  • Excessive yellow or green mucus

People with an increased risk for bacterial infections, such as the elderly, individuals with compromised immune systems, or a history of asthma, should see a physician within the first few days.  

Q. I know antibiotics will not help me recover from a viral illness. What is your best advice on dealing with an awful cold?

Dr. Mandal: Unfortunately, it is really a waiting game—viruses typically last 7 to 10 days. They generally do not need to be treated by a physician, but there are ways you can speed up your recovery:

  • Stop smoking or stay away from people who smoke.
  • If the air is dry at home, add a humidifier.  
  • Use an over-the-counter nasal spray, but limit it to 2 to 3 days because it can cause rebound congestion.
  • Use Tylenol or Motrin to alleviate fever and muscle aches.
  • Soothe your throat with lozenges, crushed ice, and honey.
  • Rest during the day and get plenty of sleep at night.
  • Drink plenty of fluids.
  • Apply warm towels for facial discomfort.
  • Do not blow your nose too hard.
  • Wash your hands frequently to avoid spreading germs.

Q. You often use a wait-and-see approach with a virus. Do you ever play the waiting game with bacteria?

Dr. Mandal: Not usually. We can easily see ear infections, test for strep throat, and hear rattling in the chest that makes us suspicious of pneumonia. In these cases, patients need an antibiotic to feel better.

Q. What happens if my virus does not get better—can it turn into a bacterial infection?

Dr. Mandal: Sometimes a virus can weaken your immune system and damage the tissue, making it easier for bacteria to grow. That is why we tell patients to come in after 10 days.

Q. Maybe I should take an antibiotic just to cover me. Is there any harm?

Dr. Mandal: Yes, when people take antibiotics unnecessarily it causes antibiotic resistance —meaning the antibiotics do not work as well when you really need them. 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.

Q. I have green mucus. Can viruses ever produce colored phlegm?

Dr. Mandal: Yes, they can. In general, when you are healthy, mucus is colorless. Mucus helps protect your airways, but when you get an infection—viral or bacterial—it can damage the cells that line the airway. The infection releases proteins that give the mucus a green color. I am not concerned when someone is able to easily bring up yellow or green phlegm without fever or difficulty breathing. But when they have these other signs, they probably need an antibiotic.  

Q. Is there any upside—can bacteria or viruses ever be beneficial?

Dr. Mandal: There are good bacteria that live in our gut. They help with our digestion and give us protection. However, viruses are not beneficial to us at all.

Q. Do vaccines protect against bacterial infections or viruses?

Dr. Mandal: Both. Vaccines prevent serious viruses such as, the measles and the flu, by taking a small part of the virus and injecting it into your body. This allows your body to produce antibodies against that particular virus. Some seasons, however, when the flu virus mutates, the vaccine does not cover the right strain. Vaccines also protect against bacterial infections, including meningitis and whooping cough.


  1. Podcast with Soma Mandal, MD, internal medicine physician, SMG radio.
  2. Centers for Disease Control and Prevention. “CDC: 1 in 3 antibiotic prescriptions unnecessary.” Centers for Disease Control and Prevention. 1 Jan 2016. Web. 14 November 2016.