Characterization of circulating Influenza virus strains in Kolkata, India during 2006-2008
Session I: Sarkar – YI submission
Characterization of circulating Influenza virus strains in Kolkata, India during 2006-2008.
Author’s Name & Affiliation: Mehuli Sarkar1, A.S. Agrawal1, R. Dey1, H. Kaur2, M.S. Chadha3, A.C. Mishra3 and M.Chawla-Sarkar1
1 Division of Virology, National Institute of Cholera and Enteric Diseases, P-33 C.I.T. Road, Scheme XM, Beliaghata, Kolkata-700010, India.2 Indian Council of Medical Research (ICMR), New Delhi – 110 029, India.3 National Institute of Virology, Pune - 411 001, India
Influenza is an acute, highly contagious respiratory infection with a potential of causing serious illness. Identification and characterization of circulating viruses over a period of time provides information for the annual formulation of influenza vaccines to WHO and the seasonality of disease in particular region for improved interventions. Thus to evaluate the frequency of influenza virus infections and strains, surveillance was initiated for characterizing circulating influenza virus strains in Eastern India during Sept-2006- Sept-2008 in the outpatient department of hospitals in Kolkata. Nasal/throat swabs from patients (n=1495) with clinical evidence of Influenza-like illness (ILI) were collected in viral transport medium. To evaluate the molecular characteristics of circulating strains, the samples were screened simultaneously by multiplex Real time RT-PCR (rRT-PCR) using Influenza A/B, H1, H3, H5 specific primers and inoculated in MDCK cell line for virus isolation. Out of 1495 samples screened, 14.5 % were positive for Influenza A and 4% for Influenza B by rRT-PCR but only 7.65% (5.35% +2.35%) were culture positive. All culture positive samples were also positive by rRT-PCR. Thus rRT-PCR is not only sensitive but also specific and fast technique, delivering results within 6-8 h compared to 8-12 days for hemagglutination assay (HA) positive virus culture. Influenza A (H1N1) viruses continued to be dominant subtype in Eastern India during September 2006-September 2007 after which Influenza A (H3N2) and Influenza B were predominant. Age specific distribution of incidence revealed higher Influenza infection in pediatric populations (3-5 years). The Influenza peak activity was observed in June-October, corresponding with monsoon season, i.e., high relative humidity (17% positive during rainy season). No correlation was observed with maximum or minimum temperature and influenza activity. Thus the data suggests that Influenza A and B are co-circulating in the community with characteristic seasonal peak co-relating with rains.
