Urinary tract infections in children

Editorials / Commentaries

CJEM 2001;2(3):197-200

Abstract

Résumé

Diagnosing urinary tract infections in febrile infants and children: when evidence-based medicine and clinical practice collide

Introduction

The American Academy of Pediatrics (AAP) recently published practice parameters for the evaluation and treatment of urinary tract infections (UTIs) in febrile children from 2 months to 2 years of age.¹ These highlight 4 specific issues: the recognition of children at risk for UTI, the diagnosis of UTI, the short-term treatment of UTI and the use of imaging modalities in infants with proven UTI.

Subcommittee participants, including pediatricians with expertise in epidemiology, informatics, infectious diseases, nephrology, radiology and urology, developed 11 recommendations (Table 1), which were subsequently reviewed by office-based practitioners. The document¹ contains 2 non-referenced statements of particular interest to emergency physicians.

1: "Urinary tract infections are important because they cause acute morbidity and may result in long-term medical problems, including hypertension and reduced renal function."

This statement is qualified later in the document when the authors note, "the relationship between UTI in infants and young children and reduced renal function in adults has been established but is not well characterized in quantitative terms. Estimates of undesirable outcomes in adulthood, such as hypertension and end-stage renal disease are based on the mathematical product of probabilities at several steps, each of which is subject to bias and error." One wonders: Is the problem real or mathematical?

2: "Infants and young children with UTI are of particular concern because the risk of renal damage is greater in this age group and because the diagnosis is frequently challenging: The clinical presentation tends to be nonspecific and valid urine specimens cannot be obtained without invasive methods (suprapubic aspiration and transurethral catheterization)."

So how did the AAP committee reach their conclusions? The following discussion summarizes the strategies and rationale used to derive these practice guidelines.

Methodology

The AAP committee identified 2000 relevant articles and selected 430 for review. Article quality was variable and inter-rater reliability of quality scores was fair to poor.² Extracted data were recorded on evidence tables that included UTI probability, diagnostic tests performed, methods of specimen acquisition, culturing techniques, initial treatment, duration of therapy and prevalence of urinary tract abnormalities. The likely consequences of misdiagnosis, short- and long-term complications, need for imaging evaluations, and estimated costs were also considered in a formal decision analysis. The strength of the evidence was rated as strong, good, fair or opinion/consensus.

Decision analyses were performed to help clinicians weigh the overall risks and benefits of different strategies. Such analyses are helpful when decisions are made under conditions of uncertainty -- that is, when published evidence is inconclusive.³ Cost-effectiveness analysis was used to quantify the trade-off between cost and clinical effect among treatment strategies. In cost-effectiveness analysis, the additional cost per unit of improvement for different approaches is estimated based on available information. For example, in the case of a febrile child with a UTI, the least expensive strategy would be to neither diagnose nor treat (do nothing). Intuitively, this would also be the least effective strategy. Increasingly aggressive diagnostic and therapeutic strategies would add to both effectiveness and cost.

Results

Table 2 shows the estimated costs, number of untreated UTIs, number of imaging studies required and the likelihood of secondary hypertension, end stage renal disease (ESRD) and death associated with 6 UTI diagnostic strategies, assuming these strategies were applied to a hypothetical sample of 100,000 children with a 5% prevalence of UTI.

Using mathematical models, the committee concluded that culturing catheterized urine samples would provide the lowest risk of death due to sepsis or unnecessary treatment. The committee speculated that culturing bagged urine specimens would result in a slightly higher death rate related to unnecessary antibiotic therapy and imaging. This is based on the assumption that "bag" cultures are only 70% specific and that in a population with 5% prevalence 85% of positive cultures would be falsely positive. These false-positive tests would generate $47.2 million in "downstream" costs per 100,000 febrile infants, without improving clinical outcomes.

The committee also concluded that screening with leukocyte esterase (LE) or nitrite reagent strips would result in a small number of undiagnosed UTIs and would lead to 2.5 times as many imaging work-ups being obtained. Therefore, despite the lower initial cost, overall expense would be higher and clinical outcomes poorer.

Table 1 summarizes the AAP recommendations.¹ Despite these, the committee acknowledged that, in circumcised boys less than 1 year of age, the invasive strategy's benefit is equivocal and that, in children over 1 year of age, its benefit is unsupported (hence that bag urine specimens may be used for screening). The committee also suggested that in children who are not acutely ill a screening urine sample may be obtained by the "most convenient means," but that if this sample suggests infection an aspirated or catheterized specimen should be cultured.¹

Are the recommendations valid?
In assessing the validity of these recommendations, three questions should be addressed.

1. Were all important diagnostic and therapeutic strategies considered?

   The AAP committee reviewed several common strategies and considered most major complications and adverse events. Interestingly, however, they did not model a strategy that many clinicians might prefer -- that of analyzing "bag" urine and obtaining suprapubic aspiration or transurethral specimens only if the initial bag urine suggests infection.

2. Were critical determinants derived from credible sources and were primary assumptions valid?

   Unfortunately, the quality of the source articles was variable and the committee's agreement on article quality was only fair to poor. The authors failed to provide information regarding the precision of sensitivity and specificity assumptions for the diagnostic tests analyzed. In addition, the cost data upon which the model was built are probably not relevant in the Canadian setting. Importantly, the core assumption -- that employing a suboptimal screening test will lead to undiagnosed childhood UTI, which in turn will lead to adult hypertension and end-stage renal disease -- may be questionable. Certainly, the incidence of these late sequelae as related to delayed or missed diagnosis of childhood UTI is ill defined. All these factors raise doubt about the validity of the model used to derive the AAP guidelines.

3. Was the impact of uncertainty considered?

   Sensitivity analyses, which allow clinicians to explore the effect of uncertainty around model assumptions, were presented in the technical report.

How will the AAP recommendations influence ED practice?

Clinical guidelines are often not followed. The most common barriers to guideline adoption are lack of agreement with guidelines, lack of awareness of guidelines and difficulty performing the recommended behaviour.⁴ Other barriers included a lack of time and resources to stay abreast of the large volume of clinical information, limited guideline accessibility, discomfort with "cookbook medicine," the presence of contradictory guidelines and a perceived increase in liability. Along these lines, emergency physicians often view urinary catheterization and bladder aspiration as invasive, uncomfortable and time consuming. Many are unfamiliar with SPA, concerned about its potential complications, and aware of its variable success rate (from 23% to 90%).¹ In the end, the penetration of the AAP recommendations into Canadian EDs will depend on how they are viewed by the physicians working there.

The following article,⁵ by Anna Jarvis and Dennis Scolnik from the Hospital for Sick Children in Toronto, describes an approach to childhood UTI.

References

1. Practice parameter: the diagnosis, treatment, and evaluation of the initial urinary tract infection in febrile infants and young children. American Academy of Pediatrics. Committee on Quality Improvement. Subcommittee on Urinary Tract Infection. Pediatrics 1999;103 (4 pt 1):843-52.
2. Downs SM. Technical report: urinary tract infections in febrile infants and young children. The Urinary Tract Subcommittee of the American Academy of Pediatrics Committee on Quality Improvement. Pediatrics 1999;103(4): e54. Available at: www.pediatrics.org/cgi/contnet/full/103/4/54e
3. Richardson WS, Detsky AS. Users' guide to the medical literature. VII. How to use a clinical decision analysis. A. Are the results of the study valid? Evidence-Based Medicine Working Group. JAMA 1995;273:1292-5.
4. Cabana MD, Rand CS, Powe NR, Wu AW, Wilson MH, Abboud PA, et al. Why don't physicians follow clinical practice guidelines? A framework for improvement [review]. JAMA 1999;282:1458-65.
5. Jarvis A, Scolnik D. A clinical perspective on diagnosis of urinary tract infections in children [controversy]. CJEM 2000;2(3):201-2.

Dr. Spence is supported by a fellowship award from the Emergency Health Service Branch of the Ministry of Health. All opinions are those of the authors, and no endorsement by the Ministry is intended or should be inferred.