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

OBJECTIVE: To report the findings of influenza surveillance programme from Union territory of Puducherry and to document the clinical and epidemiological data of influenza viruses over a five year period from 2009 to 2013.

METHODS: Respiratory samples were collected from patients with influenza-like illness from 2009 to 2013 as part of routine diagnostic and surveillance activity. Detection of pandemic influenza A (H1N1) 2009, influenza A (H3N2) and influenza B was done using Real-time PCR.

RESULTS: Of the total 2247 samples collected from patients with influenza-like illness during the study period 287 (12.7%) and 92 (4.0%) were positive for influenza A (H1N1) 2009 and influenza A (H3N2) respectively. A subset of 557 of these samples were also tested for influenza B and 24 (4.3%) were positive. Significantly 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 influenza 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 influenza activity. This information will be useful in future planning of the vaccine schedule and influenza pandemic preparedness.