Epidemiology of influenza viruses from 2009-2013-A sentinel surveillance report from Union territory of Puducherry, India

Objective: To report the i ndings of inl uenza surveillance programme from Union territory of Puducherry and to document the clinical and epidemiological data of inl uenza viruses over a i ve year period from 2009-2013. Methods: Respiratory samples were collected from patients with influenza-like illness from 2009-2013 as part of routine diagnostic and surveillance activity. Detection of pandemic inl uenza A(H1N1) 2009, inl uenza A(H3N2) and inl uenza B was done using Real-time PCR. Results: Of the total 2 247 samples collected from patients with inl uenza-like illness during the study period 287(12.7%) and 92(4.0%) were positive for inl uenza A(H1N1) 2009 and inl uenza A(H3N2) respectively. A subset of 557 of these samples were also tested for inl uenza B and 24(4.3%) were positive. Signii cantly higher positivity rate for both viruses was observed in adults when compared with children. The peak positivity of influenza A(H1N1) 2009 was observed in 2009 followed by 2012, while that of inl uenza A(H3N2) was more uniformly distributed with the exception of 2012. Overall mortality rate due to influenza A(H1N1) 2009 was 7.6% while it was 1% for influenza A(H3N2). Each year influenza-like illness and influenza virus activity coincided with period of high rainfall and low temperature except in the first half of 2012. Conclusions: As the sole referral laboratory in this region, the data provides a comprehensive picture of inl uenza activity. This information will be useful in future planning of the vaccine schedule and inl uenza pandemic preparedness.