Clinicoepidemiological analysis of post pandemic emergence of Influenza A (H1N1) infection, in a tertiary care hospital-A retrospective analysis

Background of the study- A novel influenza A (H1N1) virus resulting from quadruple re -assortment emerged in Mexico on March 2009 and emerged as pandemic, rapidly spreading across about 178 countries with significant mortality. WHO announced the onset of post pandemic period on August 2010 with request to nations to have a close surveillance.Aim of the study- To analyze clinical and epidemiological data from influenza A (H1N1) infection positive cases, in and around Chennai city, in the post pandemic period.Materials and Methods -Throat swabs were collected from all the patients who presented with signs and symptoms suggestive of flu, during the study period (July 2011 to June 2012) and the samples were tested for H1N1 influenza virus by RT-PCR method.Results - Out of 318 cases tested, 32 (10.06 percentage ) cases were positive for Influenza A (H1N1), with majority of the patients belonging to the age group of 21-30 yrs (59.37 percentage).Females (59.37 percentage) were more commonly affected than males (40.63 percentage).10 of the positive cases(31.25 percentage) were seen in people who were living in closed community, 13 of the positive cases(40.62 percentage) occurred in health care personnel and all the positive cases were clustered during the period of April and May 2012 . Most common clinical symptom was fever (96.87 percentage) followed by cough with expectoration (71.87 percentage) and the most common combination of symptoms were fever, sore throat ,cough (15.63 percentage).Conclusion- Our study showed, localised outbreak of pandemic Influenza A (H1N1) that had occurred in summer months of post pandemic period, predominantly affecting young adults, exhibiting acute, mild self limiting illness. The study emphasis on continued surveillance ,vaccination and clinical management during the post pandemic period.