UTIs in Febrile Young Children

Urinary tract infections are the most frequent source of occult and serious bacterial infections in children 2-24 months of age. UTI should be considered in children 2-24 months old who present with a fever (temperature 100.4° F) and unknown source of infection. The American Academy of Pediatrics has published new guidelines for diagnosis, treatment, and evaluation of UTI.

Specimen Collection and Laboratory Diagnosis

Suprapubic aspiration (SPA) is the most reliable collection method, because it minimizes contamination of the sample from perineal flora. It is also the most invasive and difficult to perform, with reported success rates of 23%-90%. The next-best method is bladder catheterization, which has a sensitivity of 95% and specificity of 99%, compared with SPA. When performing catheterization, it is important to have a sterile container ready, because obtaining the specimen often stimulates the child to void.

A collection bag applied to the perineum to obtain a urine specimen is the least-invasive option, but it has high false-positive rates due to contamination – with false positive rates of 88% -99%. This high false-positive rate necessitates that a more accurate specimen be obtained before the diagnosis of UTI can be made, in order to avoid overprescribing antimicrobial therapy and conducting an unnecessary evaluation of the urinary tract.

In interpreting the urinalysis (UA), it is important to understand that the tests for nitrites are specific but not sensitive. So, there are few false-positive results – but a negative test does not reliably rule out a UTI. Leukocyte esterase has a reported sensitivity of 94% but has a specificity of approximately 70%-80%; so, false positives are common.

The diagnosis of a UTI is established by a urinalysis showing evidence of infection (pyuria, bacteriuria, leukocyte-esterase positive, or positive nitrites) and at least 50,000 colony-forming units (CFUs) per mL of a single uropathogen. The presence of bacteriuria without pyuria raises the possibility that asymptomatic bacteriuria rather than an infection is the cause of bacteria in the urine.

Clinical Evaluation

If a febrile infant with no obvious source to explain his/her fever requires antibiotic therapy due to the severity of illness, a urine specimen for culture and urinalysis collected either by suprapubic aspiration (SPA) or catheterization should be obtained before starting antimicrobial therapy.

If the need for antibiotics is not immediate, the clinician should assess the patient’s likelihood of having a UTI. Patients with a low likelihood may be clinically followed without any additional testing.

If a patient has a high likelihood of UTI, then there are two choices. The first is to obtain a urine specimen either through catheterization or SPA. The second choice is to obtain a specimen though the most convenient means and check a urinalysis. If the UA is positive for leukocyte esterase or nitrites, then a reliable specimen should be obtained through catheterization or SPA. If the UA is negative, the child can be followed clinically.

Clinical characteristics can help to determine the likelihood of a UTI. In girls, predictors of UTI include: white race, age younger than 12 months, temperature 39° C, fever for at least 2 days, and absence of another infection source. Girls with no more than one or two of these risk factors have a 1% and 2% risk, respectively, of having a UTI.

In boys, predictors of UTI include: non-black race, having a temp of 39° C, a fever lasting more than 24 hours, and absence of another source of infection. Circumcised boys with fewer than two or three risk factors have 1% and 2% probability, respectively, of having a UTI. Because the rate of UTI in uncircumcised boys is 4-20 times greater than in circumcised boys, the diagnosis of a UTI always needs to be considered in uncircumcised boys.

Treatment

Either oral or parenteral therapy can be used, with the choice based on clinical judgment – taking into account severity of illness, ability to take oral medication, and reliability of follow-up. Choice of initial therapy should be based on local sensitivity patterns and later adjusted if resistance to the chosen antibiotic is found. Duration of therapy should be 7-14 days.

Imaging

Renal and bladder ultrasonography (RBUS) should be performed on all febrile infants with UTI to assess for anatomic abnormalities. Infants who do not initially improve within the first 2 days of treatment, or who have clinically severe illness, should have RBUS during the first 2 days of illness to identify a possible renal/perirenal abscess or obstructive uropathy.

In infants who are clinically improving with treatment, it is preferable to perform the RBUS later. Performing a RBUS during the patient’s acute illness may lead to false-positive findings, because Escherichia coli endotoxin can cause temporary dilation of the renal system during acute illness.