Viruses versus Bacteria: What’s the difference?

You may have heard your baby’s pediatrician say, “We cannot treat this illness because it is caused by a virus, not a bacteria.” Just what is the difference between the two?

A virus is an infectious agent that cannot live without a host cell. Viruses contain RNA or DNA plus a protein coat. They are 100 times smaller than bacteria. There are over 5,000 types of viruses known today. A virus becomes established by attaching its protein coat to receptors on the host cell surface. It then works its way into the cell so that it can replicate itself within the cell.

A bacterium is a microorganism than consists of one cell. Bacteria come in several shapes: Spherical, rod-like, or spiral. There are many, many bacteria known today—more than five with 30 zeros after it. Bacteria are everywhere: In the soil, in water, on the body’s surface, and inside the body. Many of the bacteria are helpful to a host organism such as a human; some are killed by the immune system; and some cause infections. Bacteria multiply rapidly, often in clusters or groups.

Ninety-eight percent of the infections that babies and children get are caused by viruses. The common cold, the stomach bug, conjunctivitis, bronchiolitis, diarrhea, croup, meningitis, laryngitis, warts, molluscum (a wart like growth), and all sorts of other illnesses are usually caused by viruses in children. Occasionally, a viral infection will weaken the body’s immune system or set up a condition for a secondary bacterial infection to occur. Pneumonia, ear infections, meningitis, conjunctivitis, and urinary tract infections may be caused by either a virus or bacteria.

Diagnosing whether bacteria or a virus is to blame

In order to truly diagnose whether an infection is caused by a virus or a bacterium, you need to get a culture or do sophisticated testing. Since most times these tests are invasive, expensive, and not readily available outside of the hospital, doctors usually use their judgment to decide what is causing the infection.

Treating bacterial and viral infections

Antibiotics can be helpful for a bacterial infection but are not helpful for a viral infection. Anti-viral medications can treat viruses, but they are usually used in a hospital setting when a child is quite ill. Anti-virals are expensive and often shave off one day of an illness’s duration.

Vaccines have helped eliminate many of the life-threatening bacterial and viral diseases that afflicted earlier generations, but many are still with us. The best way to keep these critters at bay is to wash your hands frequently, and to avoid crowded areas if your baby is with you and is less than 2 months of age. Have your child get the vaccines recommended by the Academy of Pediatrics and the Center for Disease Control and follow the recommendations of your child’s pediatrician.

What has been your experience with these annoying and debilitating infections? Any hope for eradicating the common cold? (Recent news is that we may have a vaccine soon but very expensive and impractical!)

Dr. Victoria McEvoy graduated from Harvard Medical School in 1975 and is currently an Assistant Professor of Pediatrics at HMS. She is the Medical Director and Chief of Pediatrics at Mass General West Medical Group. She has practiced pediatrics for almost thirty years. She has been married to Earl for thirty six years and raised four children. She currently enjoys writing, traveling, reading, almost all sports, and spending time with her two grandsons.

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