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An asymptomatic 18 month old boy, undergoing radiological investigations after a urinary tract infection (UTI) diagnosed few months earlier, is reviewed at the clinic. According to departmental protocol, a three monthly urine culture should be submitted in infants and young children as, until the age of 4 years, they remain at risk of developing renal scars after UTIs. You wonder as to the value of this routine culture.
Structured clinical question
In an asymptomatic infant or preschool child with a history of UTI under 4 years of age [patient] does the detection and management of asymptomatic bacteriuria (ABU) on routine urine culture [intervention] decrease the incidence of symptomatic UTI or renal scarring [outcomes]?
Search strategy and outcome
Secondary sources—Cochrane Library (Issue 3, 2003): search words: (1) “urine culture” OR (2) “asymptomatic bacteriuria” OR (3) “urinary tract infection”. Database of systematic reviews: 32, 24, and 135 articles (for 1, 2, and 3 respectively), with 24, 14, and 101 complete reviews (for 1, 2, and 3 respectively). No relevant systematic review for under 4s.
PubMed (1975–2003): search words—(“urine culture” OR “asymptomatic bacteriuria” OR “urinary tract infection”) AND (“prognosis” OR “renal scar*”). Limits: child <4 years. Search outcome: 12 papers, of which two were relevant (under 4 years of age).
SumSearch: 43 articles, two relevant (already retrieved by PubMed).
See table 3.
As infants and young children are thought to remain at risk, until the age of 4 years, of developing renal scars after UTIs, some paediatric departments carry out periodical urine culture in this group, even in the absence of symptoms. In addition to the fact that urine collection and culture in preschool children under 4 years of age is not always technically easy and is associated with an unsatisfactory high risk of bacterial contamination, detection of ABU in this group would be of value if its treatment results in decreased risk of renal scarring and symptomatic UTI, without adverse effects of the therapy.
Previous reports have shown that the development of new renal scars or the progression of existing scars are very uncommon after the age of 4 years,3 and, although new scars may occasionally develop after the age of 4 years, they generally occur in the context of symptomatic UTI or acute pyelonephritis but not after ABU.4 Although there is evidence of progression of scarring in relation to ABU, there is no evidence of benefit from treatment. Studies of ABU in schoolchildren have shown that absence of treatment does not increase the risk of subsequent renal scarring after the age of 5 years5 and that bacterial strains in ABU do not commonly cause symptomatic pyelonephritis.6 However, changes in bacterial flora have been associated with recurrences of or development of acute pyelonephritis ABU.7 In children with ABU, the use of antibiotic therapy for intercurrent infections leads to a change in the urinary flora and is associated with an increased risk of pyelonephritis,8 in contrast to untreated ABU where no spontaneous changes of urinary bacteria occurs.9
We therefore reviewed all published studies to try answering specifically the structured clinical question: What is the evidence that the detection and management of ABU in preschool children under 4 years of age decrease the incidence of symptomatic UTI or renal scarring? Unfortunately, we found no good quality randomised studies addressing that specific question. The two studies reviewed show that in children under 4 years of age, no new renal scarring occurred when bacteriuria was asymptomatic1 and that renal scarring only occurred in children with symptomatic recurrences associated with abnormal cystograms.2 However, both studies have obvious weaknesses: in addition to small sample sizes, there was no treatment randomisation. The first study was carried out in an unselected population of children, but not after a selected group with previous UTI which would very likely have a different natural history and prognosis. The second study was carried out exclusively in girls, who are known to have a different natural history than boys. In addition, as these studies were carried out before DMSA was available, the diagnosis of renal damage was made by intravenous urography (IVU). As DMSA is more sensitive than IVU to detect cortical scarring, some small scars may not have been recognised on IVU, although such small scars are not thought to be clinically significant. In addition, the first study did not clearly differentiate between primary and secondary (after a previous UTI) ABU.
Despite their weaknesses, which should caution about the generalisation of their findings, these studies have shown that the detection and the treatment of ABU in infants and preschool children did not decrease the risk of renal scarring. In addition, antibiotic induced modifications of the bacterial flora may increase the risk of acute pyelonephritis, and therefore the risk of cortical damage. Therefore, the practice of routine detection of bacteriuria in asymptomatic infants and preschool children is not supported by evidence1,2 and may even be harmful.7,8 Future randomised double blind controlled studies, clearly differentiating between primary and secondary ABU, with outcomes based on DMSA, are recommended.
CLINICAL BOTTOM LINE
There is no evidence to show that detection and treatment of ABU in infants and preschool children with a history of UTI decrease the risk of renal scarring.
The benefit of routine detection and treatment of ABU in such children is not supported by evidence and may even be harmful.