Urinary Tract Infections in children are mostly a matter of anatomy. They are normally caused by bugs tracking up the urethra (bit where the wee comes out) and colonising the bladder. Under normal circumstanses the bladder is a sterile environment, meaning that there is no bacteria in it. The bottom end of the urethra however, sits in an area that is not so sterile; quite close to the anus (where the poo comes out.) Needless to say, poo is not sterile. In fact, it has lots of bacteria in it. (But that is normal, it supposed to have some bacteria in it, known as 'commencals' or good bacteria.) If the bacteria stays where it supposed to (i.e. in the poo inside you and not in your bladder) then all is well. Often, however, the bacteria manages to get from the poo, or surrounding area and tracks up the urethra into the bladder, causing an infection, a 'urninary tract infection' or 'UTI', commonly known as a 'wee infection'. Due to anatomy, UTIs are much less common in boys. The bacteria needs to track all the way up the urethra (i.e. the inside of the penis) and into the bladder. This is a much longer length than in girls, in whom the bladder is quite close to the opening of the urethra.
A urinary tract infection can occur higher up in the urinary tract. A kidney infection is a 'higher urinary tract infection', know as 'pyelonephritis' whereas a bladder infection is a 'lower urinary tract infection' or 'cystitis'.
An anatomical abnormality will also predispose children to having a urinary tract infection, but they are still common in children who have entirely normal anatomy.
Symptoms of a UTI vary with the age of a child. A young child may have a temperature, vomiting, lethargy, irritability and poor feeding. Older children (generally those over 3) may also show signs of being in pain when doing a wee ('dysuria'), they may go to the toilet a lot ('frequency'). (Obviously if they are old enough they can tell you that it hurts.) You may also notice blood in their urine ('haematuria'). Other symptoms include tummy pain, offensive or cloudy urine.
If your doctor (either your GP or in the hospital) is concerned that your child has a urinary tract infection, they will do a urine sample. This is really easy with older children, you just get them to wee into a sterile pot. With younger children in nappies, it is much more difficult. The best sample to get is called a 'clean catch' and this involves sitting around with your child's nappy off, hoping to catch a drop of urine in a pot when they do a wee. There are other methods, such as a special pad that can be put into their nappy. If your doctor is really worried, they might need to put a needle into the baby's bladder and get some urine. (This is not as bad as it sounds! Sometimes it is easier than getting blood out of a baby.)
Urinary tract infections are treated with antibiotics. The antibiotics may be given by mouth or by a drip depending on how severe the illness is. The majority will clear up with antibiotics in a couple of days. Some children will also need follow up imaging such as ultrasounds.
As well as maintaining good personal hygiene (clean genital area) it is important for children (especially girls) to wipe from 'front to back' after going to the toilet. This is so that bacteria from around the anus is not brought forwards towards the urethra. Constipation can also precipitate urinary tract infections (see blog post Kids and Constipation.) Drinking sufficient amounts of water and making sure you go do a wee when you need to (i.e. not holding onto it) can also help prevent urinary tract infections.