Diseases & Conditions


Urinary Tract Infection (UTI)

A urinary tract infection (UTI) is a bacterial infection of the urinary bladder (cystitis) or the kidneys (pyelonephritis).

Urinary tract infections (UTIs) are common in childhood. Nearly all UTIs are caused by bacteria that enter the urethral opening and move upward to the urinary bladder and sometimes the kidneys. Rarely, in severe infections, bacteria may enter the bloodstream from the kidneys and cause infection of the bloodstream (sepsis) or of other organs.

During infancy, boys are more likely to develop UTIs. After infancy, girls are much more likely to develop them. UTIs are more common in girls because their short urethras make it easier for bacteria to move up the urinary tract. Uncircumcised infant boys (because bacteria tend to accumulate under the foreskin) and young children with severe constipation also are more prone to UTIs.

UTIs in older school-aged children and adolescents differ little from UTIs in adults (see Urinary Tract Infections (UTI): Introduction ). Younger infants and children who have UTIs, however, more commonly have various structural abnormalities of their urinary system that make them more susceptible to urinary infection. These abnormalities include vesicoureteral reflux (an abnormality of the ureters—the tubes connecting the kidneys to the bladder—that allows urine to pass backward from the bladder up to the kidney) and a number of conditions that block the flow of urine. As many as 50% of newborns and infants with a UTI and 20 to 30% of school-aged children with a UTI have such abnormalities.

Up to 50% of infants and preschool children with a UTI—particularly those with fever—have both bladder and kidney infections. If the kidney is infected and reflux is severe, 5 to 20% of children go on to have some scarring of the kidneys. If there is little or no reflux, very few children have scarring of the kidneys. Scarring is a concern because it may lead to high blood pressure and impaired kidney function in adulthood.

Symptoms and Diagnosis

Newborns and infants with a UTI may have no symptoms other than a fever. Sometimes they do not eat well, are sluggish (lethargic), vomit, or have diarrhea. Older children with bladder infections usually have pain or burning during urination, a need to urinate frequently and urgently, and pain in the bladder region. They may have difficulty urinating or holding urine (incontinence). Urine may smell foul. Children with kidney infections typically have pain in the side or back over the affected kidney, fever, chills, and a general feeling of illness (malaise).

A doctor diagnoses a UTI by examining the urine. Toilet-trained children may provide a urine sample by urinating into a cup after thoroughly cleaning the urethral opening. Doctors obtain urine from younger children and infants by inserting a thin, flexible, sterile tube (catheter) through the urethral opening into the bladder. In infants, the doctor sometimes withdraws urine from the bladder with a needle inserted through the skin just above the pubic bone. Urine collected in plastic bags taped to the child's genital region is not helpful because it is often contaminated with bacteria and other material from the skin.

To detect white blood cells and bacteria in the urine, which occur in UTI, the laboratory examines the urine under a microscope and performs several chemical tests. The laboratory also performs a culture of the urine to grow and identify any bacteria present. The culture is the most significant of these tests.

In general, boys of all ages and girls younger than 2 years who develop even a single UTI need further tests to look for structural abnormalities of the urinary system. Older girls who have had recurring infections also need these tests. The tests include ultrasound, which identifies kidney abnormalities and obstruction; and voiding cystourethrography, which further identifies abnormalities of the kidneys, ureters, and bladder and can identify when the flow of urine is partially reversed (reflux). For voiding cystourethrography, a catheter is passed through the urethra into the bladder, a dye is instilled through the catheter, and x-rays are taken before and after the child urinates. Another test, radionuclide cystourethrography, is similar to voiding cystourethrography, except that a radioactive agent is placed in the bladder and images are taken using a nuclear scanner. This procedure exposes the child's ovaries or testes to less radiation than voiding cystourethrography. However, radionuclide cystourethrography is much more useful for following the healing of reflux than for diagnosing it, because the structures are not outlined as well as in voiding cystourethrography. Another type of nuclear scanning may be used to confirm the diagnosis of pyelonephritis and identify scarring of the kidneys.

Prevention and Treatment

Prevention of UTIs is difficult, but proper hygiene may help. Girls should be taught to wipe themselves from front to back (as opposed to back to front) after a bowel movement to minimize the chance of bacteria entering the urethral opening. Avoiding frequent bubble baths, which may irritate the skin around the urethral opening of both boys and girls, may help lessen the risk of UTIs. Circumcision of boys lowers their risk of UTIs during infancy by about 10 times, although it is not clear whether this advantage by itself is a sufficient reason for circumcision. Regular urination and regular bowel movements may lessen the risk of UTIs.

UTIs are treated with antibiotics. Children who appear very ill or whose initial test results suggest a UTI are given antibiotics before culture results are available. Otherwise, doctors wait for culture results to confirm the diagnosis. Children who are very ill and all newborns receive antibiotics by injection either intramuscularly or intravenously. Other children are given antibiotics by mouth. Treatment typically lasts 7 to 14 days. Children who require tests to diagnose structural abnormalities often continue antibiotic treatment at a lower dose until tests are complete.

Some children with structural abnormalities of the urinary tract require surgery to correct the problem. Others need to take antibiotics daily to prevent infection. Certain mild abnormalities go away on their own and require no treatment.

Last full review/revision June 2006 by Geoffrey A. Weinberg, MD

Source: The Merck Manual Home Edition