Prevalence and epidemiology of pandemic H1N1 strains in hospitals of Eastern India

A novel Influenza A (pH1N1) virus which emerged in April, 2009, spread rapidly across the continents to become pandemic by June, 2009. In Eastern India, testing for influenza was initiated in June, 2009 and continued through July, 2010 to determine prevalence and epidemiological character of circulating pandemic H1N1 strain. Real time PCR was done on nasal and throat swab samples of patients with influenza like symptoms of those who sought medical care in local government hospitals. Of 2971 patients tested, 382 (12.86%) were positive for influenza A and 103 (3.47%) for influenza B. Of 382 influenza A positives, 284 (74.35%) and 98 (25.65%) were subtyped as pandemic H1N1 (pH1N1) and seasonal H1N1 and H3N2, respectively. The novel pH1N1 virus followed typical influenza seasonality in Eastern India and revealed a unimodal peak in July and August, correlating with the rainy season. Most of the positive cases presented with mild ILI symptoms with minimal serious complications. Though four deaths were attributed to pH1N1 infection in 2010, all four had underlying serious medical complications. Infection rate was highest in age group of >55 years followed by 5 - <18 years of age group.   Key words: Pandemic, H1N1, influenza.