A. Urinary tract infection (UTI) is an inflammatory process of the urinary tract due to an infectious agent. The spectrum of presentation ranges from mild lower urinary tract symptoms to a febrile and systemic illness. Variation exists in means of diagnosis, evaluation, and management of children with urinary tract infections, from method of collection of the urine specimen to timing and extent of imaging for workup of UTI.

A. About 3.5 % of children will have a UTI each year. Urinary tract infection accounts for up to 1.75 million office visits and 180 million healthcare dollars spent annually in the United States.

B. The prevalence of urinary tract infection varies with age, sex, and race.

1. Symptomatic infections occur in 1.4 of 1,000 neonates. Overall, UTIs are more common in females, but during the neonatal period (age less than 4 weeks) males are two times more likely to have a UTI compared with females. Circumcision reduces the odds of UTI by 85% in males. From 1 month to 6 months of age the incidence by sex is equal and from 6 to12 months the ratio of UTIs in males to females is 1:4. Subsequently, infections in males decrease significantly and remain low compared with females. Girls continue to be at risk for UTI with additional peaks in incidence at toilet training and with onset of sexual activity.

2. The incidence of UTI varies by race with Blacks having a much lower rate of UTI compared with Whites, Asians, and Hispanics.

C. Overall, Escherichia coli accounts for more than 80% of all urinary tract infections. Uropathogen prevalence varies significantly with sex, although E. coli is the most common uropathogen in both sexes (80% of outpatient female UTIs versus 50% of outpatient male UTIs). Klebsiella, Proteus, and Enterococcus are the next most common bacteria with Pseudomonas aeruginosa and Enterobacter also known to cause UTIs.

A. Risk Factors

In addition to specific underlying factors related to the male versus female anatomy (Table 6-1), urinary stasis and retrograde flow of urine are thought to predispose patients to UTI. Children most at risk for recurrent UTI include those with prior UTI, bladder and bowel dysfunction, and congenital anomalies of the kidneys and urinary tract (CAKUT), especially those with vesicoureteral reflux (VUR) and high-grade hydronephrosis and hydroureteronephrosis.

1. Female anatomic factors

a. In females, it is thought that bacteria can gain access to the urinary tract more easily than in males due to the perineal location of the urethral orifice and the shorter female urethra.

b. The normal perineal bacterial flora may enter the urethra. These bacteria are normally washed out with voiding without consequence. However, if there is a disruption of this normal flora (due to vaginitis, illness, stress, medication) the growth can increase and potentially allow access of enough bacteria to the bladder to cause infection.

c. In sexually active adolescents, vaginal penetration can predispose to infection.

d. Vaginal voiding can lead to increased moisture in the perineum allowing for bacterial overgrowth. These children will often complain of “smelly” urine and/or underpants.

2. Male anatomic factors

a. Foreskin: In infants, an intact foreskin increases the incidence of urinary tract infection 10 times compared with males who have been circumcised. The inability to retract the foreskin is a normal physiologic occurrence in newborn males. At birth, only 4% of males have a completely retractable foreskin. Over time, the foreskin will gradually loosen and become retractable via three mechanisms including penile growth, erections, and smegma production. By 3 years of age, 90% of males will have a retractable foreskin and less than 1% will have phimosis by 17 years of age. The prepuce can serve as a reservoir for potentially uropathogenic bacteria. Studies have demonstrated the P-fimbriated E. coli is more adherent to the inner preputial skin

3. Prior UTI: Children with UTI have a recurrence rate of 30% within 1 year of initial UTI. The rate increases to 50% over a 5-year period.

4. Bladder and bowel dysfunction: Bladder and bowel dysfunction (BBD) is the combination of functional constipation and lower urinary tract symptoms. Constipation has been shown to be prevalent in up to 50% of cases of children presenting with bladder dysfunction. The pathophysiology of BBD is unclear. Rectal distention that comes with constipation may have a mass effect on the bladder, which in turn leads to urinary dysfunction. Another plausible theory is that the rectal and urinary sphincters originate from a common neural network, which is dysfunctional. Children with BBD and any grade of VUR have a higher risk of recurrent febrile or symptomatic UTIs compared with children with high-grade VUR alone (56% versus 30%).

5. Congenital anomalies of the kidneys and urinary tract (CAKUT) includes, but is not limited to, vesicoureteral reflux, ureteropelvic
junction obstruction, megaureter, ureterocele, posterior urethral valves, hydronephrosis, hydroureteronephrosis, ureterovesical junction obstruction, prune belly syndrome, bladder exstrophy, and neurogenic bladder abnormalities.

a. Vesicoureteral reflux (VUR): VUR is the retrograde passage of urine from the bladder to the upper urinary tract (ureters and kidneys). Children with VUR have a higher incidence of recurrent UTI, although the exact pathophysiology is unclear. The cycling of urine in the setting of moderate and severe VUR is likely a nidus for infection. Moreover, there is increased risk that cystitis converts to pyelonephritis in the presence of VUR. Among children with first-time febrile UTI, VUR is present in about 40% of cases. Reflux is related to the muscle backing of the ureter as it enters the bladder wall (Fig. 6-1). Inadequate length of the submucosal muscular backing can lead to VUR. The anatomy of concave (A) and convex (B) renal papillae can also be a risk factor for pyelonephritis, with concave papillae thought to be more susceptible to refluxing urine into the soft tissue in the kidney (Fig. 6-2).