Urinary tract infections in children: why they occur and how to prevent them

Author: Stanley Hellerstein
Date: May 15, 1998

Urinary tract infections (UTIs) are common in children. The treatment goals are to eliminate the infection and prevent kidney damage. The usual approach in children is to first treat the infection and then obtain imaging studies of the urinary tract. This article focuses on why children have UTIs and what can be done to prevent them.

Factors That Predispose Children to UTIs

Circumcision

Uncircumcised male infants appear to be at increased risk of UTIs in the first three months of life. In a study of 100 otherwise healthy infants ranging in age from five days to eight months and admitted to the hospital because of a first known UTI,[1] most of the UTIs in infants younger than three months of age were in males, but female infants predominated thereafter. The fact that 95 percent of the male infants in the study were not circumcised led to speculation that the uncircumcised male has an increased susceptibility to UTI--at least early in life.

This issue was examined in a retrospective study at Tripler Army Medical Center.[2] The study showed that uncircumcised boys had a 4.1 percent incidence of UTI during their first year of life, while girls had an incidence of 0.5 percent and circumcised males an incidence of 0.2 percent. Subsequently, a large retrospective study of infants cared for in U.S. Army hospitals supported the theory that circumcision protects against UTIs in young male infants. The periurethral area was found to be more frequently and more heavily colonized with uropathogens, especially Escherichia coli, in uncircumcised infants than in circumcised infants.[3]

Winberg and associates[4] offer an explanation for the high incidence of UTIs in uncircumcised male infants in an intriguing article, "The Prepuce: A Mistake of Nature?" They suggest that one unphysiologic intervention--circumcision--serves to counterbalance the effect of another unphysiologic state of affairs--exposure of the infant to the microbiologic environment of the maternity unit. In a natural biologic setting, with no perineal shaving or cleansing, mothers often defecate when giving birth in a squatting or kneeling position. Because of this, the infant is colonized at birth with the mother's aerobic and anaerobic bacteria. The infant receives specific protection against infection from these bacteria through immunoglobulins transferred from the mother during gestation and after delivery in the mother's breast milk.

In contrast, babies born and cared for in a hospital are likely to be colonized by strains acquired from the external environment, against which their mothers may have no immunity. Such infants have little protection against infection from hospital-acquired strains of E. coli that colonize the gastrointestinal tract, the perineum and the periurethral area in females and preputial area in uncircumcised males. Colonization of the prepuce by these potentially dangerous bacteria places the uncircumcised male at high risk for a UTI. Circumcision diminishes that risk.

Changes in the Periurethral Flora

It is not only in the male that the character of the periurethral flora is a key factor in the occurrence of UTIs. After the first few months of life, UTIs occur far more frequently in girls than in boys, presumably because of the shorter length of the female urethra. Following birth, heavy periurethral colonization with aerobic bacteria normally becomes established in both sexes.[5] Colonization with E. coli and enterococci diminishes during the first year and normally becomes light after five years of age.

Adult women prone to recurrent UTIs have colonization of the periurethral area with the specific microbe that will cause the next infection.[6] Similar findings were demonstrated in studies of UTIs in school-aged girls.[7-8] The periurethral area is colonized by both anaerobic and aerobic bacteria from the gastrointestinal tract, which serve as part of a normal defense barrier against pathogenic microorganisms.

Two studies indicate that breast feeding protects against UTIs, both during the time the infant is receiving breast milk and for a period after breast feeding is discontinued, presumably by promoting a stable intestinal flora with fewer potentially pathogenic strains.[9,10] Disturbance of the normal periurethral flora fosters colonization by potential uropathogens. Experimental and clinical studies show that resistance to colonization by uropathogens can be broken down by administration of amoxicillin or a first-generation cephalosporin (Cephadroxil).[11] Of special interest is a study of girls with respiratory infections treated with trimethoprim-sulfamethoxazole; the study showed that this antimicrobial agent did not disturb the normal flora.[12]

Voiding Dysfunction

Voiding dysfunction is characterized by some or all of the following: urgency, frequency, dysuria, hesitancy, dribbling of urine and overt incontinence. Symptoms of voiding dysfunction may be secondary to a UTI or to local irritants such as pinworm infestation or bubble bath, or hypercalciuria.

In the anatomically and neurologically normal child, voiding dysfunction is usually caused by persistence of an unstable urinary bladder, an important contributor to recurrent UTIs. An unstable urinary bladder is a common functional disorder and usually has been present since daytime urinary control was first developing in the child. The outstanding characteristic is persistent urinary urgency.

Recognition and management of voiding dysfunction is the area in which the physician can be most effective in the prevention of recurrent UTIs. A girl with voiding dysfunction is at increased risk for recurrent UTIs because of reflux of urine laden with bacteria from the distal urethra into the bladder.[13] Studies have demonstrated that reflux of contrast material from the distal urethra into the bladder occurs when continence is maintained by contraction or compression of the bladder outlet rather than by the normal neurogenic inhibition of the detrusor contraction. Normally, the distal urethra is not sterile but has a flora similar to that of the periurethral area. When urinary leakage is prevented by compression of the urethral sphincter during an uninhibited contraction, the flat bladder base becomes funnel shaped and the posterior urethra is filled with urine. Shortly thereafter, when the contraction subsides, bacteria-laden urine from the urethra may reflux back into the bladder. Reflux of contaminated urine into the bladder, which itself may have an increased susceptibility to infection because of ischemia resulting from uninhibited detrusor contraction, is the explanation for recurrent UTIs in many children.

A relationship between constipation and UTIs is well known.[14] It has been shown that constipation per se, with a dilated rectum, causes the same pattern of voiding dysfunction as that encountered in children with persistence of an unstable bladder. Effective treatment of the constipation results in normalization of bladder function and cessation of UTIs.[15]

Prevention of UTIs

The first step in the prevention of UTIs in the neurologically intact child with an unobstructed urinary tract is to ask, "Why does this child have a UTI at this time?" A detailed voiding and defecation history should be obtained. Recent treatment of an upper respiratory infection with amoxicillin or a cephalosporin may indicate the need to try to avoid prescribing these agents for the child in the future. However, if amoxicillin or a cephalosporin is required for treatment of an upper respiratory infection, it is important not to discontinue therapy with nitrofurantoin (Macrodantin) or trimethoprim-sulfamethoxazole (Bactrim, Septra) in the child who is receiving suppressive antimicrobial therapy to prevent recurrent UTIs. We frequently encounter a child with recurrence of a UTI when this happens, possibly because of the effect on the periurethral flora or because of the high incidence of amoxicillin-resistant E. coli.

Physical examination should include careful inspection of the lumbosacral area for signs of underlying dysraphism (pilonidal sinus, tuft of hair, etc.). A rectal examination should be performed to detect a large fecal reservoir, even if there is no history of constipation.

Voiding dysfunction is treated with the use of a voiding retraining program that emphasizes good voiding technique, usually following a timed voiding schedule. In many instances a pharmacologic agent such as oxybutynin (Ditropan), propantheline (ProBanthine) or hyoscyarnine sulfate (Levsin) is helpful. The goal is to eliminate the episodes of urinary urgency, during which there may be reflux of bacteria-laden urine from the distal urethra into the urinary bladder. Anticholinergic agents not only alter bladder function but also suppress intestinal motility, so attention to constipation must be ongoing.

UTI Prevention Myths

[2.] Wiswell TE, Smith FIR, Bass JW. Decreased incidence of urinary tract infections in circumcised male infants. Pediatrics 1985;75:901-3.

[3.] Wiswell TE, Miller GM, Gelston HM Jr, Jones SK, Clemmings AF. Effect of circumcision status on periurethral bacterial flora during the first year of life. J Pediatr 1988; 113:442-6.

[4.] Winberg J, Bollgren I, Gothefors L, Herthelius M, Tullus K. The prepuce: a mistake of nature? Lancet 1989; 1 (8638):598-9.

[5.] Bollgren I, Winberg J. The periurethral aerobic bacterial flora in healthy boys and girls. Acta Paediatr Scand 1976;65:74-80.

[6.] Kraft JK, Stamey TA. The natural history of symptomatic recurrent bacteriuria in women. Medicine 1977;56:55-60.

[7.] Bergstrom T, Lincoln K, Orskov F, Orskov I, Winberg J. Studies of urinary tract infections in infancy and childhood. 8. Reinfection vs. relapse in recurrent urinary tract infections. Evaluation by means of identification of infecting organisms. J Pediatr 1967;71:13-20.

[8.] Kunin CM, Deutscher R, Paquin AJ. Urinary tract infection in school children: epiderniologic, clinical and laboratory study. Medicine 1964;43:91-130.

[9.] Marild S, Jodal U, Mangelus L. Medical histories of children with acute pyelonephritis compared with controls. Pediatr Infect Dis J 1989;8:511-5.

[10.] Pisacane A, Graziano L, Mazzarella G, Scarpellino B, Zona G. Breast-feeding and urinary tract infection. J Pediatr 1992;120:87-9.

[11.] Winberg J, Herthelius-Elman M, Mollby R, Nord CE. Pathogenesis of urinary tract infection-experimental studies of vaginal resistance to colonization. Pediatr Nephrol 1993;7:509-14.

[12.] Lidefelt KJ, Bollgren I, Nord CE. Changes in periurethral microflora after antimicrobial drugs. Arch Dis Child 1991;66:683-5.

[13.] Bauer SB. Neuropathology of the lower urinary tract. In: Kelalis PP, King LR, Belman AB, eds. Clinical pediatric urology. 3d ed. Philadelphia: Saunders, 1992:399-440.

[14.] O'Regan S, Yazbeck S, Schick E. Constipation, bladder instability, urinary tract infection syndrome. Clin Nephrol 1985;23:152-4.

[15.] Loening-Baucke V. Urinary incontinence and urinary tract infection and their resolution with treatment of chronic constipation of childhood. Pediatrics 1997;100:228-32.

[16.] Winberg J. What hygiene measures are advisable to prevent recurrent urinary tract infection and what evidence is there to support this advice? Pediatr Nephrol 1994;8:652.

[17.] Kunin CM. Urinary tract infections in adults. In: Kunin CM, ed. Urinary tract infections. 5th ed. Baltimore: Williams & Wilkins, 1997:129-56.

[18.] Kunin CM. Pathogenesis of infection: the invading microbes. In: Kunin CM, ed. Urinary tract infections. 5th ed. Baltimore: Williams & Wilkins, 1997:280-321.

[19.] Ericsson NO, Von Hedenberg C, Teger-Nilsson AC. Vulvourethral reflux: a fiction? J Urol 1973;110: 606-8.

[20.] Avorn J, Monane M, Gurwitz JH, Glynn RJ, Choodnovskiy I, Lipsitz LA. Reduction of bacteriuria and pyuria after ingestion of cranberry juice. JAMA 1994;271:751-4.

[21.] Dick PT Feldman W. Routine diagnostic imaging for childhood urinary tract infections: a systematic overview. J Pediatr 1996;128:15-22.

[22.] Report of a Working Group of the Research Unit, Royal College of Physicians. Guidelines for the management of acute urinary tract infection in childhood. J R Coll Physicians Lond 1991;25:36-42.

[23.] Koff SA. A practical approach to evaluating urinary tract infection in children. Pediatr Nephrol 1991; 5:398-400.

[24.] Haycock GB. A practical approach to evaluating urinary tract infection in children. Pediatr Nephrol 1991;5:401-2.

[25.] Gleeson FV, Gordon I. Imaging in urinary tract infection. Arch Dis Child 1991;66:1282-3.

[26.] Belman AB. Commentary. Pediatr Nephrol 1997,11:180-81.

[27.] MacKenzie JR, Fowler K, Hollman AS, Tappin D, Murphy AV, Beattie TJ, et al. The value of ultrasound in the child with an acute urinary tract infection. Br J Urol 1994;74:240-4.

[28.] Sreenarasimhaiah V, Alon US. Uroradiologic evaluation of children with urinary tract infection: are both ultrasonography and renal cortical scintigraphy necessary? J Pediatr 1995; 127:373-7.

[29.] Stark H. Urinary tract infections in girls: the cost-effectiveness of currently recommended investigative routines. Pediatr Nephrol 1997; 11: 1747.

[30.] Elder JS, Peters CA, Arant BS Jr, Ewalt DH, Hawtrey CE, Hurwitz IRS, et al. Pediatric vesicoureteral reflux guidelines panel summary report on the management of primary vesicoureteral reflux in children. J Urol 1997;157:1846-51.

STANLEY HELLERSTEIN, M.D., is professor of pediatrics at the University of Missouri-Kansas City School of Medicine and a member of the Section of Pediatric Nephrology at Children's Mercy Hospital, also in Kansas City, Mo. He graduated from the University of Colorado School of Medicine, Denver, and completed an internship and pediatric residency at Indiana University Medical Center, Indianapolis. After a two-year fellowship in fluid and electrolyte metabolism at the University of Kansas School of Medicine, Kansas City, Kan., and Children's Mercy Hospital, Dr. Hellerstein spent six years in private practice. He then returned to Children's Mercy Hospital, where he founded the Section of Pediatric Nephrology. Over the past 25 years, the evaluation and management of children with urinary tract infections has been the focus of much of his clinical, research and scholarly efforts.

Address correspondence to Stanley Hellerstein, M.D., Section of Pediatric Nephrology Children's Mercy Hospital, 2401 Gillham Rd., Kansas City, MO 64108. Reprints are not available from the author.

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