Urinary tract infection (UTI) is defined as the presence of multiplying micro-organisms (bugs) in the tract through which urine flows from the kidneys via the bladder to the outside world. UTI is 50 times more common in women, with about 5 per cent per year developing symptoms. UTI is uncommon in men below 60 years of age, but the frequency is similar in men and women in older age groups. The condition ranges from cystitis (a mild but distressing inflammation that is limited to the bladder) to severe infections of the kidney such as pyelonephritis (when the infection has reached the kidney tissue itself). Therapy depends on how and why the infection shows itself. Most patients respond rapidly to antibiotic therapy and are unlikely to have any other urinary tract abnormality.

Symptoms differ, depending on whether the infection affects the lower (bladder and urethra) or upper (kidneys and ureters) parts of the urinary tract. The symptoms of lower urinary tract infectoin are dysuria (burning on passing urine), frequency (frequent need to pass urine) and urgency (compelling need to urinate). The urine can be cloudy with an offensive odour. In older men, generalised symptoms such as confusion and incontinence can be present. Urine infections are much commoner in the elderly, due to poor bladder emptying, an enlarged prostate, or incontinence associated with stroke or dementia.

The symptoms of upper urinary tract infection are the same as lower tract symptoms plus loin (flank) pain, fever and chills. The patient is likely to be ill and might require hospital admission.