​The most common symptom of urinary tract infection is a painful, burning sensation when passing urine. Urinary tract infections are caused by bacteria entering the urethra and multiplying in the bladder. They are usually treated successfully with antibiotics prescribed by a doctor. Urinary tract infections are quite common, especially among women and children. 
Normal urine is sterile and contains no germs such as bacteria, viruses, or fungi. Urinary tract infections (UTIs) occur when bacteria enter the urinary tract via the urethra. UTIs are most commonly caused by bacteria that normally live in the bowel.
The urinary tract consists of the kidneys, bladder, ureters, and urethra. The urethra is the opening to the urinary tract where urine comes out.
​UTI can be classified by the area of the urinary tract that it affects:

• When only the urethra is affected it is known as urethritis
• When the bladder is affected it is known as cystitis (the most common form of UTI)
• When the kidneys are affected it is known as pyelonephritis, which can cause kidney damage if left untreated.