Abstract :
Introduction: Influenza A and its subtypes, classified under the Myxovirus family, are among the primary causes of acute viral respiratory tract infections in humans. Symptoms of influenza-like illness include fever, headache, myalgia, prostration, coryza, sore throat, and cough. This viral infection spreads rapidly worldwide through seasonal epidemics, outbreaks, and pandemics, leading to significant morbidity and mortality. In tropical countries like India, the seasonality of Influenza A (H1N1) pdm09 is less clearly defined. Due to the lack of data on its burden and seasonal trends in the study region, this study aims to address these gaps.
Materials and Methods: This retrospective observational study was conducted using data collected from the Department of Microbiology. Samples received in Microbiology Department for Influenza A (H1N1) pdm09 test from suspected cases of SARI patients of tertiary care hospital from 2016 to September 2024 were selected. Data from patients outside the tertiary care hospital were excluded. SARI was defined as any person having breathlessness, not able to maintain oxygen saturation, positive xray findings or person of > 5 years old presenting with symptoms of acute lower respiratory infection with sudden onset of fever ?38 °C, and cough or sore throat, AND shortness of breath or difficulty breathing with in the last 7 days, AND requiring hospitalization.
Results: Burden of influenza A (H1N1) pdm09 from patients of a tertiary care institute was 1% in 2016, 22% in 2017, 0.0008% in 2018, 21% in 2019, 20% in 2020, 0% in 2021 and 2022, 4% in 2023 and 22% in 2024 till September month. The seasonal trend of cases was observed in August, September, and October during 2016, 2017, and 2018. However, this pattern shifted to January, February, March, and April in 2019 and 2020. In 2023, cases were detected in September, whereas in 2024, the highest number of cases occurred in July and August.
Discussion: The overall burden of Influenza A (H1N1) pdm09 was found to be 21%, with fewer cases reported in 2016, 2018, 2021, and 2022. The decline in cases during 2021 and 2022 may be attributed to the COVID-19 pandemic and its associated preventive measures. A noticeable shift in seasonality was observed, transitioning from the late fall and winter months to the heavy rainfall season. Understanding influenza burden and seasonal trends is crucial for optimizing vaccination timing and implementing effective preventive measures in the region.
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