A urinary tract infection (UTI) is an infection that affects a part of the urinary tract. Lower urinary tract infections may involve the bladder (cystitis) or urethra (urethritis) while upper urinary tract infections affect the kidney (pyelonephritis). Symptoms from a lower urinary tract infection include suprapubic pain, painful urination, frequency and urgency of urination despite having an empty bladder. Symptoms of a kidney infection, on the other hand, are more systemic and include fever or flank pain usually in addition to the symptoms of a lower UTI. Rarely, the urine may appear bloody. Symptoms may be vague or non-specific at the extremities of age (i.e. in patients who are very young or old).
The most common cause of infection is E. coli, though other bacteria or fungi may sometimes be the cause. Risk factors include female anatomy, sexual intercourse, diabetes, obesity, catheterisation, and family history. Although sexual intercourse is a risk factor, UTIs are not classified as sexually transmitted infections (STIs). Pyelonephritis usually occurs due to an ascending bladder infection but may also result from a blood-borne bacterial infection. Diagnosis in young healthy women can be based on symptoms alone. In those with vague symptoms, diagnosis can be difficult because bacteria may be present without there being an infection. In complicated cases or if treatment fails, a urine culture may be useful.
