Corresponding Author: Moslehi Mohammad Ashkan, MD, Department of Pediatrics, Nemazee Hospital , Shiraz University of Medical Sciences, Shiraz , Iran . E-mail: moslehim@sums.ac.ir

DIAGNOSIS

Diagnosis of UTI is based upon culture of an organism from an appropriately collected specimen of urine. An abnormal urinalysis must be confirmed by a positive urine culture.

Urinalysis
A urinalysis typically includes microscopic assessment of the number of white blood cells (WBC) per high powered field (hpf) of a centrifuged specimen of urine. However, the sensitivity, specificity and positive predictive value of pyuria, defined as 5 WBC per hpf, to correlate with a positive urine culture are low.^34,35 Prediction of UTI is improved when hemocytometer WBC counts are performed on uncentrifuged specimens, as recommended in adults.³⁶ In a study of febrile (rectal temperature >38º C) infants younger than eight weeks of age in which UTI occurred in 13.6 percent, hemocytometer WBC 10/µL had a higher sensitivity (82 versus 59 percent) compared to standard urinalysis.35 Dipsticks that detect the presence of leukocyte esterase and nitrite are available commercially; the former corresponds to significant pyuria and the latter to Enterobacteriaceae, which convert urinary nitrate to nitrite. In adults, the dipstick has a sensitivity and specificity of 95 and 75 percent, respectively.³⁷ The positive predictive value is 30 to 40 percent (when tested in patients suspected of possible UTI), and the negative predictive value is 99 percent. Dipsticks may be used for rapid and easy screening. However, urine culture must always be performed in an infant in whom UTI is suspected. The presence of organisms on a Gram stain of 0.01 mL of unspun urine correlates with subsequent growth in a urine culture of >10(5) CFU in adults. This density of bacteria rarely is recovered in a urine culture from neonates. Even if urine Gram staining were readily available, it rarely would be performed in infants for this reason.

• Urine collection
  Specimens should be obtained by suprapubic bladder aspiration or catheterization. Collections in a bag frequently are contaminated, and a midstream clean catch specimen is impractical in newborns.
 
• Suprapubic aspiration
  Suprapubic aspiration of the bladder urine is the most reliable technique to identify bacteriuria .31The technique is simple, relatively safe, and causes minimum discomfort. The procedure should be performed in infants who have a palpable bladder and who have not voided recently. After cleaning the suprapubic area with an antiseptic solution, a 23- or 25-gauge needle is inserted perpendicular to the baby, approximately one centimeter above the pubic symphysis. In one report, ultrasound guidance improved the yield of urine compared to unguided aspiration (96 versus 60 percent) .³²Any growth of urinary pathogens is significant.
 
• Bladder catheterization
  Bladder catheterization is an alternative to suprapubic collection. Bacterial contamination resulting from incomplete cleansing of the perineal area or prepuce renders this technique less reliable than suprapubic aspiration. In a study comparing catheterization to bladder aspiration in febrile infants younger than one year of age, catheterization cultures with >1000 CFU/mL had a sensitivity and specificity of 95 and 99 percent, respectively .³³

Sepsis evaluation As noted above, approximately one-third of newborns with UTI have an accompanying bacteremia, and some have meningitis. Thus, a blood culture should be obtained in all infants in whom UTI is suspected, and culture of the cerebrospinal fluid (CSF) should be considered. Infants at increased risk for fungal infection should be evaluated for disseminated disease.

TREATMENT

Treatment with intravenous broad-spectrum antimicrobial agents should be initiated as soon as cultures of urine, blood, and CSF (if indicated) have been obtained. Ampicillin and gentamicin provide coverage for the most common bacterial pathogens. Experts vary in their dosing recommendations. In term infants younger than seven days old, the American Academy of Pediatrics Red Book recommends ampicillin (25 to 50 mg/kg per dose Q8 hour IV) and gentamicin (2.5 mg/kg per dose Q12 hour IV).38 Other experts use once-daily gentamicin dosing (4 mg/kg per dose Q24 hour IV).39 Vancomycin (10 to15 mg/kg per dose Q12 hour IV for infants < 7 days and Q8 hours thereafter) usually is substituted for ampicillin in infants with later onset infections to provide empiric coverage for hospital-associated infections, including coagulase-negative staphylococci, Staphylococcus aureus, and Enterococcus species. If meningitis is suspected, the higher doses of antibiotics must be used, pending the results of cultures .38 Antibiotics should be tailored when the results of the cultures and the antimicrobial susceptibilities become available. Sterilization of the urine should occur within 48 hours of treatment with the appropriate antimicrobial agent. Optimally, it should be confirmed by repeating the urine culture at that time. If bacteriuria persists despite appropriate therapy, the urinary tract and other sites should be investigated to determine a potential reservoir of infection.

The duration of antibiotic therapy is 10 to 14 days for newborns with uncomplicated bacterial UTI. We complete the treatment course in newborns with intravenous antibiotics, although older infants often are switched to oral antibiotics after clinical improvement. Longer treatment is needed for fungal infections.

Conventional teaching holds that the urine culture should be repeated two to three days following the completion of treatment. However, because suprapubic aspiration or repeat catheterization would be required, it often is omitted if the patient is clinically stable. Antibiotic prophylaxis with low-dose amoxicillin (15 to 20 mg/kg per day PO) is started until a radiographic evaluation has been performed to detect urinary tract abnormalities. Continuation of this prophylaxis depends upon the results of imaging studies.