A bacterial infection is an infection caused by bacteria. Bacterial infections can often be treated successfully with antibiotics.

An infection may begin as a bacterial infection, or a bacterial infection may follow a viral infection that does not get better. When a viral infection doesn't get better for 10 days or more, or when a viral infection starts to improve and then unexpectedly gets worse, a bacterial infection may be more likely.

A bacterial infection usually affects a single area in the body, such as the sinuses, lungs, ears, or urinary tract. Common bacterial infections include sinusitis, pneumonia, strep throat, ear infections, and bladder infections. If untreated, a bacterial infection can spread to the bloodstream, a condition called bacteremia.