Background and objectives: Influenza virus is a typical human pathogen causing serious respiratory illness resulting in significant mortality throughout the globe. Andhra Pradesh witnessed the first case of influenza A H1N1 in India from Hyderabad (now in Telangana) on May 16, 2009. In the recent past, Andhra Pradesh witnessed exponential increase in the number of confirmed cases of influenza infection. In this study, we present the salient features of the recent outbreak of influenza during 2017-2018 in the state of Andhra Pradesh, first of its kind after the division of the state.
Materials and methods: Clinically, suspected cases of influenza-like illness received in the Virus Research and Diagnostic Laboratory, Department of Microbiology, Sri Venkateswara Institute of Medical Sciences (SVIMS), Tirupati, from January 2017 to May 2018 were included in the study. The samples were tested for influenza A, influenza A (H1N1) pdm09, influenza A (H3N2), influenza B, influenza B/Yamagata and influenza B/Victoria.
Results: A total of 1286 samples were received for testing. The positive samples were influenza A unsubtypable (109), influenza A (H1N1) pdm09 (356), influenza A (H3N2) (38) and influenza B (19; Victoria - 2, Yamagata - 17). There was no significant difference in positivity between genders with 260 (49.81%) females and 262 (50.19%) males being positive.
Conclusion: The outbreak started in the late monsoon (January) of 2017 and had two peaks; one in summer months and another in winter months. Influenza B virus was reported from December 2017 to May 2018. Age groups ≤5 years and 6-18 years had higher positivity as compared to other age groups. Regular surveillance programmes are required for assessing the trends of influenza infections due to various subtypes and to plan timely and adequate steps for preventing the spread to larger vulnerable population.
Keywords: Andhra Pradesh; India; influenza; outbreak.