Urinary tract infections are fairly common in children, especially girls, and when doctors worry about recurrence, they often prescribe antibiotics preventively.

But the practice not only does not reduce the risk of reinfection, a new study says, but it also may make it more likely that a new infection will be resistant to drugs.

The findings do not mean that the infections should not be treated with antibiotics, said the senior author of the study, Dr Ron Keren of The Children's Hospital of Philadelphia. Untreated infections can lead to serious kidney problems.

"The question is, after you have that first infection, does putting a patient on a daily low dose of antibiotic prevent recurrent urinary tract infections?" Keren said. Since the drugs can be given for several years, the researchers said doctors should discuss the pros and cons with families before beginning them. The study appears in the current Journal of the American Medical Association. The lead author is Dr. Patrick H Conway. The researchers based their findings on a review of the medical records of more than 70,000 children under age 6 over a period of almost five years. Many of the children had a urine reflux condition that often leads to infection. A better approach may be to carefully monitor children believed to have a reflux problem.