What are bacteria and viruses?

While bacteria and viruses can both cause mild to serious infections, they are different from each other. This is important to understand, because bacterial and viral infections must be treated differently. Misusing antibiotics to treat viral infections contributes to the problem of antibiotic resistance.

Bacteria and viruses, too tiny to be seen by the naked eye, can cause similar symptoms, such as a sore throat, and are often spread in the same way, but that’s where the similarities end.7,19

A bacterium is a single, but complex, cell. It can survive on its own, inside or outside the body. Most bacteria aren’t harmful. In fact, we have many bacteria on and inside our body, especially in the gut, to help digest food.7,19

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 host’s healthy cells.19

Bacteria cause bacterial infections, such as throat infections, and viruses cause viral infections. It is important to know whether a bacterium or virus is the cause of an infection, because the treatments differ. Examples of bacterial infections include whooping cough, strep throat, ear infection and urinary tract infection (UTI). Viral infections include the common cold, flu, most coughs and bronchitis.7

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 for a ‘culture’ test to have the bugs identified under a microscope.19

Doctors usually treat bacterial infections with antibiotics. They either kill bacteria or stop them multiplying. But since antibiotic resistance is a growing problem, antibiotics may be prescribed only for serious bacterial infections.7

The treatment of viral infections can include:7

  • managing symptoms, such as using honey for coughs and drinking warm fluids, like chicken soup for oral hydration;
  • taking paracetamol to relieve fever;
  • stopping viral reproduction using local antiseptics, antiviral medicines, such as medicines for HIV/AIDS and cold sores;
  • preventing infection in the first place, such as using vaccines for flu and hepatitis