A kidney infection occurs when bacteria travel from the bladder up the ureters and into the kidneys. Sometimes kidney infections may occur when bacteria in the blood enter the kidneys.

Symptoms of kidney infection may include:

• Painful urination and other symptoms of a bladder infection.
• Pain in the flank, which is felt just below the rib cage and above the waist on one or both sides of the back.
• Fever.
• Nausea and vomiting.

Oral antibiotics usually can treat kidney infections. But a brief hospital stay and a short course of intravenous (I.V.) antibiotics are sometimes required. If not treated with antibiotics, the infection may damage the kidneys. The infection may also spread to the bloodstream and become life-threatening, especially in young children and the elderly.