A urine infection is caused by germs (bacteria) that get into the urine. Most urine infections are due to bacteria that normally live in the large bowel. They cause no harm in the bowel but can cause infection if they get into other parts of the body. Some bacteria lie around the back passage (anus) after a stool (faeces) has been passed. These bacteria can sometimes travel to the urethra (the tube that passes urine from the bladder) and into the bladder. Some bacteria thrive in urine and multiply quickly to cause infection.

Urine infections often cause painful burning and stinging when passing urine, a need to pass urine frequently, fevers, nausea and vomiting. A urine sample is needed to confirm if a urine infection is present.
The infection is commonly just in the bladder (when it is called cystitis), but may travel higher up to affect one or both kidneys as well(this is called pyelonephritis).

Nearly 1 in 20 boys, and more than 1 in 10 girls, have at least one urine infection by the time they are 16 years old. Children aged under 5 years are the most commonly affected.

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