Epidemiology of Human Metapneumovirus (HMPV) in India: a cross-sectional study.

Background: The Department of Health Research, Ministry of Health and Family Welfare, India, established the Virus Research and Diagnostic Laboratory Network (VRDLN) in 2014 to strengthen viral diagnostic capabilities and provide a system for routine virological surveillance. In 2022, we also initiated the Model for Integrated Influenza Surveillance in Tamil Nadu (MIST) to enhance surveillance of virologic and clinical characteristics of severe acute respiratory infections (SARI) cases in selected sentinel tertiary care hospitals. This study investigates the epidemiology of Human Metapneumovirus (HMPV) in India by analysing data from these distinct but related surveillance systems. Methods: We analysed VRDLN data from 2019 to 2024 to describe HMPV cases based on time, place, and personal characteristics. We presented a comparison of two periods-2019 to 2023 and 2024-to compare historical trends with the current scenario. We also examined detailed clinical and laboratory profiles of HMPV-positive SARI cases collected under the MIST project from 2022 to 2024 (a case series). Hospitals under the VRDLN conducted testing of any physician-referred patient, while MIST exclusively tested SARI patients who met a standardised case definition. While the VRDLN provided an overall picture of the testing and positivity trends, MIST provided details on laboratory parameters, and clinical course and outcomes of positive cases. All laboratories adhered to standardised quality-assured testing protocols and reported data to a centralized database. Findings: Between 2019 and 2023, the VRDLN tested 20,625 patients for HMPV, of whom 1030 (3.2%) were positive. In 2024, 11,155 patients were tested, with 367 (3.3%) confirmed positive. Across both periods, age-stratified analysis indicated that the majority of tests were conducted among children. The highest positivity was observed in those aged 1-2 years, with 4.5% (128/2864) testing positive in 2019-2023 and 4.6% (70/1508) in 2024. Most HMPV-positive cases presented with Acute Respiratory Infection (ARI)/Influenza-like illness (ILI), accounting for 85.4% [566/17,090] of cases in 2019-2023 and 40.3% [148/1697] in 2024, as most testing was carried out among these patients. Fever and cough were the most common symptoms, reported in 70.3% of cases from 2019 to 2023 and 79.6% (292/8398) in 2024, and in 60.5% (401/12,059) and 60.8% (223/5977) of cases, respectively. Under the MIST project, we tested 3599 SARI patients between 2022 and 2023, identifying 28 (0.8%) HMPV-positive cases. Patients experienced a median illness duration of 11 days (interquartile range [IQR]: 7.5-14.5) and stayed in the hospital for a median of 7 days (IQR: 5-9.5). Eight cases required intensive care for a median of 3.5 days (IQR: 2.5-6), while 12 cases needed oxygen support for a median of three days (IQR: 3-5.5). Among the 28 cases, 25 (89.3) showed clinical improvement at discharge, and 22 (84.6) were healthy at a one-month follow-up. As of April 2025, 12 patients remained healthy, one experienced recurrent lung complications, and six were lost to follow-up. Interpretation: The increased testing and higher positivity rates in 2024 highlight the growing recognition of HMPV as a significant respiratory pathogen in India. However, we noted no recent change in the epidemiological features of HMPV. Strengthening surveillance networks remains critical to understanding the burden of such emerging viral pathogens and guiding public health policies. Although HMPV detection in our surveillance population indicates a potential association with illness, it should not be regarded as definitive evidence of causation. Moreover, hospitalisation duration should be interpreted in the context of potential unmeasured co-infections and comorbidities, rather than being solely attributed to HMPV infection. Funding: Funded by the Department of Health Research, Ministry of Health and Family Welfare, Government of India.