146: Urinary Tract Infection

I. DEFINITION

Urinary tract infection (UTI) is the presence of pathogenic bacteria or fungus in the urinary tract.

II. INCIDENCE

Various series report an incidence of 0.5–1.0% in term infants weighing >2500 g and higher rates (3–5%) in premature infants or infants weighing <2500 g. Escherichia coli remains the most common pathogen, followed by other gram-negative rods.

III. PATHOPHYSIOLOGY

Inoculation of the normally sterile urinary tract is thought to occur via fecal-perineal contamination, instrumentation, or spread from an infectious process outside of the urinary tract.

IV. RISK FACTORS

Any altered anatomy (ie, posterior urethral valves, vesicoureteral reflux, ureteropelvic junction obstruction) or derangement in normal bladder function predispose to UTI. For hospital-acquired infections, indwelling Foley catheters or recent instrumentation are the most common risk factors. In addition, uncircumcised males and patients with systemic infectious processes or immunosuppression are at greater risk.

V. CLINICAL PRESENTATION

Infants may appear acutely toxic (respiratory distress, apnea, bradycardia, hypoglycemia, poor perfusion) or present with nonspecific findings of lethargy, irritability, poor feeding, vomiting, jaundice, or failure to thrive.

VI. DIAGNOSIS

1. Laboratory studies

   1. Urine culture. Suprapubic aspiration or bladder catheterizations are the only 2 methods of obtaining a reliable urine culture in a neonate (see Chapters 25 and 26). Cultures obtained from a suprapubic bladder aspiration or urethral catheterization that grow >50,000 colony-forming units of a single organism and have evidence of pyuria on urinalysis are interpreted as positive. Clean-catch or collection bag specimens often are inaccurate due to contamination and are only clinically reliable if the culture demonstrates no growth. Urine culture is no longer recommended in infants <72 hours of age in an early-onset sepsis workup and is more appropriately done for late-onset sepsis workup.

   2. Urinalysis. Leukocyte esterase is the most sensitive (83%) finding on a urinalysis and has a specificity of 78%. The presence of nitrites is 98% specific but is only has a sensitivity of 53%. Detection of bacteria by microscopy has high interexaminer variability, but is as high as 81% sensitive and 83% specific in some hands. No single finding is diagnostic; however, when there is microscopic bacteriuria or pyuria in addition to the presence of leukocyte esterase or nitrites, a urinalysis is >99% sensitive and 70% specific.

VII. MANAGEMENT

1. Initial antibiotic treatment. For the majority of neonatal cases, initial treatment with broad-spectrum intravenous (IV) antibiotics is appropriate (usually Ampicillin and Gentamicin). In nontoxic infants over a month of age, oral therapy has been found to be as efficacious as IV therapy. (For dosages and other pharmacologic information, see Chapter 148.)

2. Further investigations. All neonates with a febrile UTI or suspected anatomic abnormality require renal/bladder ultrasonography, and voiding cystourethrogram (VCUG). The American Academy of Pediatrics guidelines no longer recommend VCUG at the ...