Ask Dr. Marla – Infections: Bacteria vs Viral

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What’s the difference between bacterial and viral infections?


Viruses and bacteria are both so-called microorganisms that can cause infections, but the similarities end there. Typically a virus is smaller than a bacteria and needs either people, animals or plants to survive. When we think of a virus we often think of colds or the flu. A common bacterial infection parents might be familiar with is strep throat. What is critical to know is that antibiotics are effective against bacteria, but ineffective against viruses. Unless of course that bacteria is resistant to the antibiotic. Antibiotic resistance is a growing concern in the medical community.

When your child has a sore throat, it is impossible to know by looking at the throat if the cause is a bacteria or a virus. That is why your doctor swabs the area. If no bacteria is found, we know the infection is caused by a virus.

Did you know that as many as 200 different viruses can cause the common cold? That helps to explain why you can get more than one cold in a season. SickKids Hospital points out that most children can expect anywhere from six to 12 colds in a year. Typical treatment for a cold is rest, fluids and medication to reduce fever if it’s making your child uncomfortable (such as ibuprofen or acetomenophin). This is what we call supportive care. Keep your child at home if he or she has a fever. Since antibiotics are powerless against a virus, we rely on the body’s immune system to fight the virus through the production of antibodies.

Viruses are more contagious than bacteria which is why colds and flus spread so easily. To curb the spread, wash your hands often and avoid touching your face, as you may be unaware of what is lingering on your fingertips.

Typically, fever is present the first few days with a viral infection, but can last up to a week with influenza. Vitamins and herbal preparations have not been shown to prevent colds.

A viral illness can develop into a secondary bacterial infection, which could present with another fever, more trouble breathing or a change in behaviour. If you are unsure what is causing your child’s illness, see your doctor.


Dr. Marla Shapiro is a medical doct or, author, broadcaster, lecturer and parent.

Originally published in ParentsCanada magazine, February 2014.

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