Etiology and Pathogenesis

Although some of the mechanisms are unclear, certain populations of children are at higher risk for UTIs. In the neonatal period, uncircumcised boys are at the highest risk of infection followed by girls and circumcised boys. Uncircumcised neonates presenting with fever have an incidence of approximately 20% versus 2% for circumcised boys. Two theories that potentially explain this discrepancy are the unkeratinized skin of the uncircumcised foreskin being more prone to bacterial invasion and relative tightness of the infant foreskin causing possible partial obstruction of the urethral meatus. It should be noted, however, that despite the elevated risk, UTIs are still a rare event in uncircumcised boys. Outside the neonatal period, girls are at higher risk for infection than boys, and the incidence decreases in both sexes with age. Other important host risk factors include familial predisposition, race, sexual activity, underlying anatomy, urinary function, and manipulation of the urinary tract (most commonly in the form of bladder catheterization). Two problems warranting further discussion are dysfunctional elimination syndrome (DES) and vesicoureteral reflux (VUR), the retrograde passage of urine from the bladder into the upper urinary tract.

DES is a very common and often underdiagnosed problem affecting the otherwise healthy pediatric population. It is characterized by abnormal voiding or stooling patterns, incontinence, and observed withholding maneuvers. In school-aged children, evidence suggests that DES plays a significant role in UTIs and the persistence of VUR. VUR is the most common urologic abnormality in children, found in 1% of the population and up to 40% of children with febrile UTIs. VUR is graded 1 to 5 with 95% grade 3 or better, and the majority of mild cases self-resolving by age 1 year. Children with VUR are at increased risk for recurrent UTIs. Furthermore, VUR may also increase the risk of pyelonephritis renal scarring, although evidence has not shown a clear correlation.

Infections of the urinary tract begin with ascension of flora that transiently colonize the lower urinary tract. The most common organism responsible for infection is the enteric gram-negative organism Escherichia coli. Other gram-negative organisms include Klebsiella, Proteus, Citrobacter, and Enterobacter spp. Gram-positive infections by enterococcus, Staphylococcus saprophyticus, and rarely Staphylococcus aureus are also known to occur. For infection to take place, the organisms must not only be present in the urinary tract but also needs to attach, adhere to, and invade the mucosa and epithelium. The bacteria are then able to ascend via the epithelial cells to the bladder and kidney (Figure 93-1). It is thought that genetically determined variation in the host’s defense against this process may explain the familial association of UTIs among first-degree relatives.

Figure 93-1 Cystitis.

Clinical Presentation

UTIs can present in a variety of ways with varying differentials depending on the age of the patient. In general, the older the patient, the more specific the presentation will be. In infants and small children (younger than 2 years of age), UTIs may only present with fever. Certainly, fever without a clear source should prompt the clinician to consider a UTI, but even in infants with another potential source, evaluation of the urine may still be prudent. Other symptoms may include irritability, poor feeding, or failure to thrive. Of note, parental report of “foul-smelling urine” has not been shown to correlate with UTIs. The differential diagnosis, as with all infants with fever and an unknown source, is extensive, but the clinician should primarily be concerned about occult bacteremia, sepsis, and viral infections. Other aspects of the history that may be helpful are the degree and duration of the fever and any history of UTIs in the patient or family.

In older children, presentation is more similar to that of the adult. Symptoms may include fever, abdominal pain, urinary symptoms (dysuria, urgency, incontinence, hematuria, frequency), back pain, or vomiting. The differential diagnosis can vary greatly depending on the presentation. For the urinary symptoms, the differential diagnosis includes urinary calculi, urethritis (chemical, sexually transmitted infection), vaginal foreign body, and DES. The differential for fever and abdominal pain in older children includes group A streptococcus infections, Kawasaki’s disease, appendicitis, and gastroenteritis, the first three of which may also present with pyuria. In the patient’s history, it is also important to note any history of: UTIs in the patient or family, VUR or DES, constipation, or poor growth.

On physical examination of an infant or child with suspected UTI, it is important to note the degree of fever (if present) and any signs of cardiovascular instability that would reflect severe illness. Other findings on examination, more common in older patients, may include suprapubic or costovertebral tenderness. A complete abdominal examination should be performed to assess for any abdominal masses or abnormal distension of the bladder. A genital examination should look for any signs of urethritis or vulvovaginitis and for any anatomic abnormalities. If the patient is febrile, attention should also be paid to other potential sources of fever (Figure 93-2).

Figure 93-2 Common clinical and laboratory features of acute pyelonephritis.

Evaluation and Management (Table 93-1)

Laboratory Evaluation

The appropriate management of a patient with UTI can vary significantly depending on the severity of illness. Those with mild to moderate illness can be effectively managed as outpatients, but those with severe illness may require inpatient or even intensive care and dialysis. Because of the often nonspecific nature of presentation, laboratory analysis of the urine is essential to confirm the diagnosis in all settings. Two important steps for the clinician as they evaluate the patient are (1) whether to obtain a urine sample and (2) how best to do so.

Table 93-1 Summary of Treatment and Workup of Patients at Risk for Urinary Tract Infection

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