Clinical utility of Myxovirus resistance protein A (MxA) for differentiation between viral and bacterial infection in adult acute care: a prospective observational study

Distinguishing between viral and bacterial infections remains a diagnostic challenge with major implications for treatment and appropriate antibiotic use. This study aimed to evaluate the performance of Myxovirus resistance protein A (MxA) as a marker of viral infection in acutely ill adult patients. A total of 869 consecutive adult patients was allocated into groups based on the presence or absence of infection and its etiology. The effectiveness of MxA and MxA-based ratios in identifying viral infections was evaluated and results were compared with an optimal statistical model obtained through multiple linear regression analysis. Confounding factors influencing MxA production were identified. Additionally, we developed an algorithm to guide antibiotic prescription in a subgroup of patients with respiratory tract infections. MxA was significantly elevated in viral infections and coinfections. With an AUC of 0.87, a sensitivity of 79.8% and a specificity of 87.1% at an optimal cut-off of 21 µg/l, MxA exhibited a high diagnostic yield. Combining MxA with CRP and procalcitonin further enhanced its performance and was comparable to that of the optimal statistical model. The magnitude of MxA production differed by viral etiology. Comorbidities were not associated with any consistent alteration in MxA expression. MxA is a reliable biomarker for distinguishing viral from bacterial infections in acutely ill adults. The MxA/PCT ratio further improves diagnostic accuracy and may support future antibiotic stewardship strategies.