Do I Need an Antibiotic? Bacterial vs. Viral Infections

Feb 21, 2017

Bacteria vs virus – learn the difference and the best way to fight each.

Think a good dose of antibiotics will knock that cold or flu out of you? Think again. Antibiotics, if prescribed and taken correctly, usually can kill bacteria but they are useless against viruses such as the cold and flu.

Unlike bacteria, viruses generally require a vaccination to prevent them in the first place or antiviral drugs to treat them. Often, the only treatment for a viral infection is to let the illness run its course.

What’s the difference?

Bacteria: Mostly friendly

Bacteria are single-celled microorganisms that are everywhere—in the air, soil and water, on plants and in animals. Most bacteria—including those in our intestines —are harmless. Some actually help by digesting food and destroying disease-causing microbes, according to the Mayo Clinic, which notes that fewer than 1 percent of bacteria cause disease in people.

Some infections bacteria can cause include strep throat, tuberculosis, and urinary tract infections (UTI).

How is a bacterial infection treated?

Taking a prescribed course of antibiotics according to a doctor’s instructions can kill the infection. Unfortunately, bacteria are adaptable and the overuse of antibiotics has helped create strains of bacteria that have grown resistant to antibiotics. Plus, overuse of antibiotics also can kill off healthy bacteria in your body and may let toxic germs gain a foothold, according to the U.S. Centers for Disease and Control.

Virus: Invading you to stay alive

Viruses are smaller than bacteria and can’t survive without a living host. A virus attaches itself to cells and usually reprograms them to reproduce itself. Also, unlike bacteria, most viruses do cause disease.

Some virus-caused diseases include the common cold, AIDS, herpes, and chickenpox.

Viral infections require either vaccinations to prevent them in the first place—like with vaccinations against polio or the measles—or antiviral drugs to treat them.

How is a viral infection treated?

Antiviral drugs, developed largely in response to the AIDS pandemic, do not destroy a virus but inhibit its development. Antivirals also are available to treat some illnesses like the herpes simplex virus, the flu and shingles, according to Medical News Today.

Antibiotics are not effective against viruses, and the Centers for Disease Control and other health organizations now recommend against using antibiotics unless there is clear evidence of a bacterial infection.

Most viral infections tend to resolve on their own without treatment so any treatment generally is aimed at providing relief from symptoms like pain, fever and cough.

How are they spread?

Both viral and bacterial infections are spread in similar ways:

  • Coughing and sneezing
  • Contact with infected people, especially through kissing and sex
  • Contact with contaminated surfaces, food, and water
  • Contact with infected creatures, including pets, livestock, and insects like fleas and ticks

How can a doctor tell the difference?

Viruses and bacteria are tricky. Not only can they cause similar symptoms but many illnesses—like pneumonia, meningitis and diarrhea—can be caused by either a virus or a bacterium.

Your doctor often can diagnose you through a medical history and physical exam. The doctor may order blood or urine tests or a spinal culture to help pinpoint a viral or bacterial infection.

According to physicians interviewed by, most doctors consider four things when faced with a virus vs. bacteria question:

  • Have a fever? Common with both bacterial and viral illnesses. But if the flu is  circulating in your area right now, antibiotics won’t be the answer to the virus. Your doctor will look to treat your symptoms. Be sure to get a flu shot next season, if possible. 
  • Been sick long? Viral infections that linger sometimes can turn into a larger problem, such as a sinus infection when bacteria join in. Your doctor may prescribe an antibiotic.
  • What color is it? While green or yellow mucus can be a sign of a bacterial infection, doctors say that’s an unreliable indicator of the need for an antibiotic.
  • What’s your throat look like? White spots can be a sign of bacteria. A sore throat without other cold symptoms can be strep throat, which absolutely requires antibiotics. To be sure, you need a culture or rapid antigen test, which can be done while you wait.

Make yourself feel better

The CDC offers a lengthy list of non-prescription drug measures you can seek for relief of your symptoms. Besides generally getting rest of drinking plenty of fluids, here are some of the easiest ones for adults to follow:


  • Use a clean humidifier or cool mist vaporizer
  • Avoid smoking, secondhand smoke, and other pollutants
  • Take nonprescription pain relievers like acetaminophen or ibuprofen to relieve pain or fever
  • Use saline nasal spray or drops

Sore Throat

  • Ice chips, sore throat spray, popsicles, or lozenges
  • Gargle with salt water

Sinus Pain/Pressure

  • A warm compress over the nose and forehead can help relieve sinus pressure
  • Breathe in steam from a bowl of hot water or shower

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