A urinary tract infection (UTI) is an infection in the organs and tubes that process and carry urine out of the body. Most UTIs are either bladder infections (cystitis) or kidney infections (pyelonephritis).

UTIs occur most often when bacteria begin to grow in the kidneys, the bladder, the tubes that carry urine from the kidneys to the bladder (ureters), or the tube that carries urine from the bladder to outside of the body (urethra). Sexual intercourse may introduce bacteria into the urinary tract, especially in women. Catheterization is a common source of bacterial infection in people who are hospitalized or live in long-term care facilities.

An adult or older child with a UTI may have:

• Pain or burning during urination.
• An urge to urinate frequently but usually passing only small quantities of urine.
• Dribbling (inability to control urine release).
• Reddish or pinkish urine.
• Foul-smelling urine.
• Cloudy urine.

Urinary tract infections are more common in women than in men. They are also more common in older adults than in younger adults.

Treatment for most urinary tract infections is antibiotic pills and home treatment, such as drinking lots of fluids. If widespread infection (sepsis) develops or if the infection is severe or harms kidney function, hospitalization may be necessary so that antibiotics can be given directly into a vein (intravenous antibiotics).