Only 13 percent of youngsters who were given the antibiotic combination of trimethoprim plus sulfamethoxazole (brand names Bactrim and Septra) developed a urinary tract infection while on the medication compared to 19 percent of the children on a placebo, according to the study.

"There was a small benefit across many groups of children, which will be worthwhile in some -- e.g., very young children, those with severe infections and those with recurrent infections," said the study's lead author, Dr. Jonathan C. Craig, a professor of clinical epidemiology at the School of Public Health at the University of Sydney in Australia.

Results of the study are published in the Oct. 29 issue of the New England Journal of Medicine.

Urinary tract infections (UTIs) are very common in children. According to the study, 2 percent of boys and 8 percent of girls will have at least one UTI by the time they're 7 years old. Although often a mild infection, UTIs can be serious, with as many as 5 percent of children with one of these infections developing some type of kidney damage.

And that kidney damage can be long-lasting, according to Dr. Alejandro Hoberman, of the Children's Hospital of Pittsburgh, who authored an accompanying editorial in the journal.

"Some children have a condition known as vesicoureteral reflux, which with a urinary tract infection can lead to renal scarring, which can eventually lead to high blood pressure, the pregnancy complication preeclampsia and even kidney problems," Hoberman explained.

Craig's study included children with varying degrees of vesicoureteral reflux, which means urine backs up from the bladder into the kidney, as well as children without this condition. However, all of the children included in the study had had at least one symptomatic UTI.

The median age of the children at the start of the study was 14 months, and they were recruited from four centers in Australia. Just under two-thirds of the children were girls.

Half of the children (288) were randomly selected to receive the antibiotic combination preventively for 12 months, while the other youngsters received a placebo for 12 months.

The finding that 13 percent of the children receiving antibiotics developed a UTI during the study period versus 19 percent of those on placebo means that 14 children have to be treated with antibiotics to prevent one UTI from occurring, according to the study.

There were no statistically significant differences in the rates of adverse events in either group.

"This study is a welcome addition to the literature. It was a larger sample of children and had a control group with placebo, but there were only modest treatment effects. I think it's probably not a one-size-fits-all approach. There may still be subgroups of children [like those with reflux] who may benefit more," said Hoberman.

But, he added, "I'm not ready to completely discount antimicrobial prophylaxis yet. Let's not throw the baby out with the bathwater."

Craig said he believes the modest reduction in urinary tract infections with preventive antibiotic use outweighs the potential risks, such as the possible development of antibiotic-resistant bacteria.

More Information

To learn more about urinary tract infections in children, visit the U.S. National Institute of Diabetes and Digestive and Kidney Diseases.