Prevalence and Surveillance of Influenza Viruses in Hospitalized Patients with Respiratory Infections in and Around Chennai, Southern Part of India.

The COVID-19 pandemic has heightened concerns about increasing cases of human influenza virus, which pose a significant public health threat to the population in and around Chennai. Therefore, this study analyzed the prevalence of influenza viruses, including influenza A (InfA) and its subtypes H1N1 and H3N2, influenza B (InfB), and respiratory syncytial virus (RSV), in the population of Chennai and surrounding areas. The study included 444 nasopharyngeal and oropharyngeal samples collected between September 2022 and March 2023 from hospitalized patients with severe respiratory symptoms. The sample group consisted of 249 men and 195 women between the ages of 1 and 100 years. The collected samples were processed for detection of InfA, H1N1, H3N2, InfB, and RSV according to the guidelines of the Indian Council of Medical Research (ICMR) and the Department of Public Health, Government of Tamil Nadu. InfA and H3N2 were found to be the most prevalent, with prevalence rates of 11.4%, and 5.1%, respectively. They were followed by H1N1 (3.1%), InfB (2.02%), and RSV (0.5%). H3N2 was more frequently observed in adults and elderly aged groups (4.5%). The most common symptoms associated with InfA infection were fever, body aches, cough, and headache. In addition, RSV, H1N1, and H3N2 viral positivity (11.4%, 5.1%, and 0.5%, respectively) were higher in children aged 1-5 years. This study shows that H1N1 and H3N2 viruses were the predominant strains during the study period in Chennai and provides valuable information for public awareness and preventive measures against early influenza virus infections.