Researchers have developed and validated a clinical prediction rule that can help identify febrile infants age 60 days and younger who are at low risk for serious bacterial infection (SBI). The rule is based on urinalysis, absolute neutrophil count (ANC) and procalcitonin levels.

“Once further validated on an independent cohort, clinical application of the rule has the potential to decrease unnecessary lumbar punctures, antibiotic administration, and hospitalizations,” the Febrile Infant Working Group of the Pediatric Emergency Care Applied Research Network (PECARN) writes in JAMA Pediatrics, online February 18.

Between 8 and 13 percent of young febrile infants have SBIs, including urinary-tract infection (UTI), bacteremia and bacterial meningitis, Dr. Nathan Kuppermann of University of California Davis School of Medicine in Sacramento and colleagues point out.

To derive and validate their prediction rule, they assembled a cohort of 1,821 febrile infants (mean age, 36 days; 42 percent female, 43 percent white and non-Hispanic, 20 percent black and 29 percent Hispanic).

SBIs were present in 170 infants (9.3 percent), including 26 (1.4 percent) with bacteremia, 151 (8.3 percent) with UTI, and 10 (0.5 percent) with bacterial meningitis; 16 infants (0.9 percent) had concurrent bacterial infections.

In the derivation cohort of 908 infants, a negative urinalysis, ANC of 4,090/uL or less and a serum procalcitonin of 1.71 ng/mL or less identified a low-risk group of 522 infants, with an SBI risk of 0.2 percent. The sensitivity of the prediction rule in the derivation set was 98.8 percent.

In the validation cohort of 913 infants, the rule identified a low-risk group of 497 infants with an SBI risk of 0.4 percent, yielding a sensitivity of 97.7 percent. The negative predictive value was 99.6 percent and the negative likelihood ratio was 0.04.

One infant in the derivation cohort (with Enterobacter cloacae bacteremia) and two infants in the validation set (with UTIs with negative urinalyses) with SBIs were misclassified by the prediction rule. No infants with bacterial meningitis were missed by the rule.

“Importantly,” say the researchers, “the rule does not require CSF data, potentially obviating the need for routine lumbar punctures for many young febrile infants provided that further external validation confirms accuracy. Furthermore, the rule is straightforward and uses objective variables, simplifying implementation.”

They note, however, that while the sample included 170 patients with SBIs, only 30 had bacteremia or bacterial meningitis, “reflecting the current epidemiology of SBIs in this age group. Therefore, validation of our findings on cohorts with greater numbers of invasive infections is desirable before implementation. Finally, until further validation of the prediction rule, clinicians must remain most cautious with infants younger than 28 days, in whom the risks of bacteremia and bacterial meningitis as well as herpes encephalitis are the greatest,” they suggest in their article.