Predictors, patterns and outcomes of Human Metapneumovirus in a hospitalized cohort.

<bold>Background:</bold> Since the COVID-19 pandemic, increased numbers of Human Metapneumovirus (HMPV) have been observed, suggesting an epidemiological shift. Despite this, comprehensive data on the clinical profile and severity of HMPV, and comparison to well-studied viruses, Influenza and Respiratory Syncytial Virus (RSV), remains limited. <bold>Methods:</bold> A retrospective cohort study analysed positive Respiratory Multiplex PCR tests of adult cases admitted to the Royal Melbourne Hospital between 01 January 2021 and 31 October 2023. Cohorts included HMPV (n=117), RSV (n=72) and Influenza (n=54). <bold>Results:</bold> Compared to Influenza, the HMPV cohort was older (mean age;63 vs 52 years, p<0.01), more co-morbid, per the Charlson Comorbidity Index (CCI) (mean CCI;4.39 vs 2.83, p<0.01), and had higher rate of hospital admission (86.3% vs 66.7% p<0.01). No differences were found between HMPV and RSV cohorts. Multivariate analysis found HMPV hospitalisation positively correlated with greater CCI and underlying respiratory disease (p<0.01). HMPV cohort had the highest rate of viral pneumonia (64.2%, vs Influenza 30.7%, p<0.01;vs RSV 46.3%, p=0.02) which positively correlated with High Dependency Unit (HDU) admission (p<0.01) and all-cause mortality during admission (p<0.01). No differences were observed in hospital stay, ventilation, HDU admission, or all-cause mortality between cohorts. <bold>Conclusion:</bold> HPMV is an under-recognised cause of significant respiratory illness and hospitalization with a propensity for viral pneumonia. Further, morbidity and mortality outcomes of HMPV are similar to those of hospitalised Influenza and RSV cases. Acknowledging and understanding this impact is essential for effective public health strategies.