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What is the difference between bacterial and viral infections?

3-minute read

Key facts

  • Bacteria are single cells that can survive on their own, inside or outside the body.
  • Viruses cause infections by entering and multiplying inside the host's healthy cells.
  • It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms.
  • Antibiotics won't work for viral infections. Misusing antibiotics to treat viral infections contributes to the problem of antibiotic resistance.
  • Antibiotics won't cure viral infections.

How are bacteria different from viruses?

Bacteria and viruses are too tiny to see with the naked eye. They can cause similar symptoms and are often spread in the same way, but are different in most other ways.

Bacteria are single cells that can survive on their own, inside or outside the body. Most bacteria aren't harmful. In fact, you have many harmless and helpful bacteria on your skin and inside your body, especially in the gut to help digest food.

Viruses are smaller and are not cells. Unlike bacteria, they need a host such as a human or animal to multiply. Viruses cause infections by entering and multiplying inside the body's healthy cells.

How are bacterial infections different from viral infections?

It can be difficult to know what causes an infection, because viral and bacterial infections can cause similar symptoms. Your doctor may need a sample of your urine, stool or blood, or a swab from your nose or throat to see what sort of infection you have.

If you have symptoms on an infection, it is important to know if it is caused by bacteria or viruses, because the treatments differ.

Examples of bacterial infections include whooping cough, strep throat, ear infection and urinary tract infection (UTI).

Examples of viral infections include the common cold and flu, most coughs and bronchitis, chickenpox, monkeypox, COVID-19 and HIV/AIDS.

What treatment will I receive for bacterial and viral infections?

Treating a bacterial infection

Doctors usually treat bacterial infections with antibiotics. It's important to match the antibiotic with the specific type of bacterial infection you have. The right antibiotic will kill bacteria or stop them multiplying.

Antibiotic resistance is a growing problem in Australia and the world. It is caused, in part, by overuse of antibiotics in humans, animals and the environment. This is one of the reasons why your doctor will only prescribe antibiotics when they are confident that the benefits of treatment are greater than the risks.

Treating a viral infection

Antibiotics aren't effective against viral infections. If you have a viral infection, your doctor may recommend one or more of the following treatments:

  • rest at home to allow your immune system to fight the virus
  • managing symptoms, such as warm drinks or chicken soup to soothe your throat and stay hydrated
  • paracetamol to relieve fever
  • stopping viral reproduction using antiviral medicines, such as medicines for HIV/AIDS and cold sores
  • preventing infection in the first place, such as vaccines for flu and hepatitis

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: September 2022

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