In ED-collected samples, the median POC MxA level was 571 (interquartile range [IQR], 240–955) μg/L in children with viral infections, 555 (IQR, 103–889) μg/L in children with viral-bacterial coinfections, and 25 (IQR, 25–54) μg/L in children with bacterial infections (P < .001). The gene discussed is MX1; the disease is viral infectious disease.