A short urethra predisposes girls to UTI. Uncircumcised maleinfants are at 5to 12-fold increased risk for UTI compared withcircumcised male infants. Obstruction to urine flow and urinary stasis is the major risk factor and may result from anatomicabnormalities, nephrolithiasis, renal tumor, indwelling urinarycatheter, ureteropelvic junction obstruction, megaureter, extrinsic compression, and pregnancy. Vesicoureteral reflux, whetherprimary (70% of cases) or secondary to urinary tract obstruction, predisposes to chronic infection and renal scarring. Scarring also may develop in the absence of reflux.
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The symptoms and signs of UTI vary markedly with age. Few have high positive predictive values in neonates, with failure to thrive, feeding problems, and fever as the most consistent symptoms. Direct hyperbilirubinemia may develop secondary to gram-negative endotoxin. Infants 1 month to 2 years old may present with feeding problems, failure to thrive, diarrhea, vomiting, or unexplained fever. The symptoms may masquerade as gastrointestinal illness with colic, irritability, and screaming periods. At 2 years of age, children begin to show the classic signs of UTI such as urgency, dysuria, frequency, and abdominal or back pain. The presence of UTI should be suspected in all infants and young children with unexplained fever and in patients of all ages with fever and congenital anomalies of the urinary tract.
The diagnosis of UTI in infants and young children requires the presence of both pyuria and at least 50,000 CFU/mL of a single pathogenic organism. For older children and adolescents, >100,000 CFU/mL indicates infection. Urine samples for urinalysis should be examined promptly (within 20 minutes) or refrigerated until cultured. Urine obtained by midstream, clean-catch technique for older children and adolescents is an appropriate collection method, whereas transurethral catheterization is the appropriate method for younger children and infants in which antibiotics are being started. Perineal bags for urine collection are prone to contamination and are not recommended for urine collection for culture. If there
Urinalysis showing pyuria (leukocyturia of >10 white blood cells [WBCs]/mm3) suggests infection, but also is consistent with urethritis, vaginitis, nephrolithiasis, glomerulonephritis, and interstitial nephritis. Urinary dipstick tests that combine both the leukocyte esterase and nitrite (or positive leukocyte esterase and positive microscopy for bacteria) have sensitivity of 70% and specificity of 99% for detecting a UTI. Either test used alone has poor sensitivity.
Ultrasonography of the bladder and kidneys is recommended for infants with febrile UTIs to exclude structural abnormalities or detect hydronephrosis. Voiding cystourethrogram (VCUG) is indicated if the ultrasound is abnormal (hydronephrosis, scarring, or other findings to suggest obstruction or congenital abnormality). Vesicoureteral reflux is the most common abnormality found and is ranked from grade I (ureter only) to grade V (complete gross dilation of the ureter and obliteration of caliceal and pelvic anatomy) (see Chapter 167). A technetium-99m DMSA scan can identify acute pyelonephritis and is most useful to define renal scarring as a late effect of UTI.