An infection in any part of the urinary system, the kidneys, bladder, or urethra.
Urinary tract infections are more common in women. They usually occur in the bladder or urethra, but more serious infections involve the kidney.
A bladder infection may cause pelvic pain, increased urge to urinate, pain with urination, and blood in the urine. A kidney infection may cause back pain, nausea, vomiting, and fever. Common treatment is with antibiotics.