Biomarkers and their association with bacterial illnesses in hypothermic infants

To describe the association of biomarkers with serious bacterial infection (SBI; urinary tract infection [UTI], bacteremia and/or bacterial meningitis) in hypothermic infants presenting to the emergency department (ED).

We performed a cross sectional study in four academic pediatric EDs from January 2015 through December 2019, including infants ≤90 days old presenting with a rectal temperature of ≤36.4 °C. We constructed receiver operating characteristic (ROC) curves to evaluate the accuracy of blood biomarkers including white blood cell count (WBC), absolute neutrophil count (ANC) and platelets for identifying SBI, with exploratory analyses evaluating procalcitonin and band counts.

Among 850 included infants (53.5% males; median days of age 13 [IQR 5-58 days]), SBI were found in 55 (6.5%). For infants with SBI, the area under the curve (AUC; 95% confidence interval) for WBC was 0.70 (0.61-0.78) with sensitivity 0.64 (0.50-0.74) and specificity 0.77 (0.74-0.80). The AUC for ANC was 0.77 (0.70-0.84) with sensitivity 0.69 (0.55-0.81) and specificity 0.77 (0.74-0.8). For platelets, the AUC was 0.6 (0.52-0.67) with sensitivity 0.73 (0.59-0.84) and specificity 0.5 (0.46-0.53). Both the WBC and ANC were minimally accurate for identifying hypothermic infants with SBI. When looking at the accuracy of these biomarkers for identifying invasive bacterial infection (IBI; bacteremia and/or bacterial meningitis), ANC again showed minimal accuracy with an AUC of 0.70 (0.55-0.85).

Biomarkers commonly used as part of an infectious workup are generally poor at identifying SBI in hypothermic infants. Our findings from this cohort of hypothermic infants are similar to those reported from febrile infants, suggesting similarities in the bioresponse to infection between hypothermic and febrile infants. Additional research is required to improve risk stratification for hypothermic infants, and to better guide evaluation and management.