A painful bacterial infection in a joint.

Bacterial arthritis happens when a bacterial infection moves to a joint. It's most common in infants and older adults. The infection most often affects knees. But it also can affect hips, shoulders and other joints. Quick treatment is needed to keep joints from being damaged.

Besides pain, symptoms include joint swelling and trouble using the joint. The joint can be swollen, red and warm. There might be fever.

Treatment involves draining the joint. Antibiotics are often given through a vein in the arm at first. Then antibiotics taken by mouth might be used.