Influenza virus and its subtypes circulating during 2018-2019: A hospital-based study from Assam.

Purpose: Influenza virus can cause serious respiratory illness sometimes resulting in epidemics and pandemics associated with significant morbidity and mortality across the globe. Hence, continuous surveillance of the activity of the influenza virus and its subtypes is necessary to help the policy makers to take effective and appropriate decisions regarding its control. The study aimed to determine distribution of influenza viruses in Assam of north-east India having subtropical climate that may lead to viral subtype divergence.

Methods: Clinically suspected ninety cases with Influenza like illness (ILI) were included, irrespective of age and sex during the period 1st July 2018 to 30th June 2019. Aseptically collected Nasopharyngeal swabs in viral transport media (VTM) were tested by conventional Reverse Transcriptase Polymerase Chain Reaction (RT PCR) for detection of Influenza A and Influenza B viruses which were further processed for detection of subtypes such as H1N1 pdm09, H3N2 and Influenza B (Yamagata and Victoria lineage). Normally distributed continuous variables were summarised by mean and standard deviation. All categorical variables were summarised as percentages.

Results: Influenza activity was seen in 42.2% of ILI cases with male predominance (57.9%). Influenza A was the predominant type (84.2%). Among the subtypes, A(H1N1) pdm09 was predominant (76.3%) followed by Influenza B (Victoria lineages) (15.8%) and AH3N2 (7.9%). Significant difference was observed between different subtypes with regard to age distribution only. Influenza activity in Assam showed two seasonal peaks; the primary one from May to July and the secondary from November to February.

Conclusion: The study described the distribution of different Influenza viruses and its subtypes in Assam along with their seasonal activities. These findings will help to formulate the policy for its prevention and control in Assam as well as to monitor the efficacy of the current influenza vaccine.