In children aged older than 2 months, the pediatrician is often faced with the scenario of fever with no apparent source. Because symptoms in young patients are nonspecific and reliable urine samples require invasive testing, there can be a delay in both diagnosis and treatment of urinary tract infections (UTIs). This delay may be associated with increased risk of renal scarring and a longer duration symptomology for the young child.1-3
Assessing the patient
When the pediatrician believes that immediate antibiotic therapy is warranted for the febrile infant without an identifiable source, a urine sample for culture should be obtained through either suprapubic aspirate (SPA) or catheterization as part of the workup. Given that antibiotics are commonly used in pediatric practice, failure to do so will sterilize the urine and likely make diagnosis of UTI more difficult or mask the diagnosis altogether.4,5
Whereas the complete management of infants with fever without a source (FWS) is beyond the scope of this article, it has been addressed in older as well as newer clinical practice guidelines.6,7
The pediatrician also needs to consider the following genitourinary system diagnoses when caring for a patient with fever and no obvious source of infection:
· Asymptomatic bacteriuria may occur in 1% to 3% of younger children and in 1% of older children. It usually resolves spontaneously without any significant or long-term complications or symptoms.8-11
· Among children presenting with fever and no source of infection, the risk of UTI is much greater (7%) than the risk of occult bacteremia among infants appropriately immunized (1%).12-14
· A number of diseases other than UTI have a similar presentation including group A streptococcal infection, appendicitis, and Kawasaki disease.
Urine cultures obtained through catheterization have a sensitivity and specificity of 95% and 99%, respectively, compared with samples obtained though SPA. Bag cultures are found to have an unacceptably high false-positive rate (88%–95% depending on the pretest probability of UTI). Guidelines from the American Academy of Pediatrics (AAP) state that the only utility of a bagged culture is if negative, and that if the pediatrician plans on initiating treatment, urine should be obtained from either a catheterized or SPA specimen.4,5
What is the risk of UTI?
When the pediatrician does not believe that immediate antibiotics are warranted, the guideline allows for different paths based on “low likelihood” of UTI. Although the guideline does not provide a definition or provide specific action steps based on “low likelihood,” it does provide flexibility allowing the pediatrician to set a 1% or 2% threshold of UTI as “low likelihood.”
The overall rate of UTI in young children with FWS is 5%. Young females are more than twice as likely to have a UTI in this scenario compared with boys. The rate of UTI in circumcised boys is 0.2% to 0.4% with uncircumcised boys having a 4-times to 20-times increased risk over that baseline. When another source of infection is identified, the risk of UTI is decreased by 50%.5
Probability of UTI in girls is less than or equal to 1% when not more than 1 risk factor and less than or equal to 2% when no more than 2 risk factors listed in the Table are present.5
In the uncircumcised male when there is FWS, the probability of UTI is greater than 1% at baseline and less than or equal to 2% only if none of the risk factors in the Table are present. In the circumcised male, risk of infection is less than or equal to 1% when no more than 2 risk factors and less than or equal to 2% when no more than 3 risk factors in the Table are present.5
If the infant is deemed not likely to have a UTI depending on the above discussion and the pediatrician’s comfort level, it is reasonable to follow up clinically without further testing. If the pediatrician decides the patient is not a low risk, he or she can proceed with obtaining a urine specimen via SPA or catheterization. Alternatively, a sample may be obtained via another method, and only proceeding to SPA or catheterization if the urinalysis suggests UTI-positive leukocyte esterase, nitrite, pyuria, or bacteriuria.5