Background: Prompt differentiation of viral from bacterial infections in febrile children is pivotal in reducing antibiotic overuse. Myxovirus resistance protein A (MxA) is a promising viral biomarker.

Methods: We evaluated the accuracy of a point-of-care (POC) measurement for blood MxA level compared to the reference enzyme immunoassay in 228 febrile children aged between 4 weeks and 16 years, enrolled primarily at the emergency department (ED). Furthermore, we analyzed the ability of MxA to differentiate viral from bacterial infections.

Results: The mean difference between POC and reference MxA level was -76 µg/L (95% limits of agreement from -409 to 257 µg/L). Using a cutoff of 200 µg/L, POC results were uniform with the reference assay in 199 (87.3%) children. In ED-collected samples, the median POC MxA levels (interquartile range) were 571 [240-955] µg/L in children with viral infections, 555 (103-889) µg/L in children with viral-bacterial co-infections, and 25 (25-54) µg/L in children with bacterial infections (P < 0.001). MxA cutoff of 101 µg/L differentiated between viral and bacterial infections with 92% sensitivity and 91% specificity.

Conclusions: POC MxA measurement demonstrated acceptable analytical accuracy compared to the reference method, and good diagnostic accuracy as a biomarker for viral infections.