Bacterial vs. Viral Infection: What's the Difference?

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MRSA bacteria

When you get an infection, it’s usually due to a bacterial or viral infection. It’s important to know which type of infection you have, since the treatment for bacterial vs. viral infections can differ. Sometimes it can be difficult to tell these two types of infections apart, since symptoms can be similar. Yet there are key differences between the two, which can help guide care when you or your loved ones are sick.

Characteristics of Bacterial Infection vs. Viral Infection

While bacteria and viruses are both germs that can make us ill, they differ when it comes to causes, symptoms and treatment approach.

Bacteria are tiny, single-celled microorganisms that thrive in many types of environments, both inside human bodies or outside, on surfaces such as carpets, or outside in the soil. Many live throughout our bodies—on our skin or mucous membranes, and in our intestines, where they help us digest food.

While most bacteria in our bodies are beneficial, some can cause infections, such as:

  • Urinary tract infections

Viruses are smaller than bacteria. They require living hosts (people, plants or animals) to multiply and survive. When a virus enters your body, it invades cells and takes them over, causing the cells to produce more virus. However, as with bacteria, some viruses help our bodies, primarily by boosting our immune systems and fighting off disease-causing germs.

Illnesses caused by viruses include:

  • Flu (influenza)
  • Hepatitis A, B, C, D and E
  • Common colds
  • COVID-19
  • Measles
  • Poliomyelitis

Some illnesses can be caused by either viruses or bacteria. These include:

  • Ear infections
  • Pneumonia

Complications of Bacterial and Viral Infections

Sometimes, bacterial infections occur while you’re recovering from a viral illness. For example, you could develop a sinus or ear infection after getting a common cold virus, or pneumonia while ill with COVID-19 or flu.

Warning signs that you may have developed a secondary bacterial infection, and need to see your health provider, include:

  • Symptoms lasting longer than usual for a viral infection (beyond 10 to 14 days)
  • Fever worsening rather than improving

One dangerous complication of a bacterial infection is sepsis. Sepsis (which can develop into septic shock) occurs when your body’s immune system overreacts to an infection—usually a bacterial one, such as pneumonia, urinary tract infection, or bloodstream infection. It can also occur as a response to viral infections, such as influenza or COVID-19. Sepsis can cause vital organs to shut down and can be fatal. However, when caught early, sepsis can be treated with antibiotics and medications to support organ function.

Viral infections can also be dangerous, as we have seen with the COVID-19 pandemic. This virus can cause acute respiratory distress syndrome, blood clots, kidney and heart problems, pneumonia and organ failure, among other complications.

Bacterial vs. Viral Infection Treatment

Perhaps the biggest difference between bacterial vs. viral infections is in the use of antibiotics. Antibiotics are only effective against bacteria, not viruses. So, if your child’s middle ear infection is caused by a cold virus, antibiotics won’t help. If it’s caused by bacteria and is moderate to severe, your doctor likely will prescribe an antibiotic.

Unfortunately, inappropriate overuse of antibiotics has led to a rise in bacteria that are resistant to antibiotics. Doctors increasingly struggle to find an antibiotic that will work against certain bacterial infections.

Bacterial and viral infection treatment approaches overlap in some areas:


Non-antibiotic treatments are being developed to fight these antibiotic-resistant infections and slow the development of antibiotic resistance. For example, monoclonal antibodies are being used to fight both viruses like COVID-19 and bacterial infections, such as Clostridium difficile, or C. diff (a gastrointestinal illness). Monoclonal antibodies are a type of immunotherapy, which uses antibodies produced in a lab to target specific germs and activate the immune system to help combat them.

Another type of targeted treatment to fight infections uses viruses called bacteriophages, or phages for short. These are genetically engineered to fight infection-causing bacteria. Phage therapy is in the experimental stages; doctors have used it successfully in people, but it is not approved as a medical therapy.

Antiviral drugs

Antiviral medications also can help treat certain virus-caused illnesses, such as shingles, hepatitis and influenza, though they must be given soon after symptoms develop. Antiviral flu treatment can reduce the time someone is ill by about a day, plus reduce fever and lessen the severity of other flu symptoms.


Vaccines are available to prevent some viral and bacterial infections. Vaccines have long been used to prevent bacteria-caused illnesses like diphtheria, tetanus and pertussis, as well as viral infections like hepatitis, chickenpox and measles. In early December, the U.S. Food & Drug Administration approved two new vaccines to prevent COVID-19 which is caused by SARS-CoV-2 virus infection. Other vaccines are expected to be approved in 2021.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Dec 24
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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