Virological Perspectives and Characterization of Seasonal Influenza B Viruses in Mumbai

Acute respiratory infections caused by influenza viruses are major life-threatening infections affecting the global population. Information on influenza viruses in Mumbai region in India is limited. With an estimated population above one crore, it becomes imperative to identify the predominant circulating strains, seasonal evolution, epidemiology and impact of influenza virus infection on the public health of Mumbai. The present study is aimed to isolate and identify the prevalent influenza B virus strains circulating in the Mumbai region. Virological analysis of 482 throat and nasal samples from patients presenting with suspected influenza-like illness was conducted from January to December 2012 at a research institute in Mumbai. Isolation of positive influenza B samples was performed on Madin Darby Canine Kidney (MDCK) cell line. The isolates were further characterized by hemagglutination inhibition assay and one-step reverse transcriptase polymerase chain reaction. Among all the specimens tested, 71% were positive for influenza virus. The positivity for influenza B virus, influenza A (H1N1) pdm 09 and seasonal influenza A virus was 38%, 22% and 11% respectively. Of the 80 influenza B specimens cultured on MDCK, virus was isolated from 38 (48%) samples. Influenza B/Wisconsin/1/2010-like serotype belonging to the B/Yamagata/18/88 lineage was the predominant serotype identified. Influenza was a significant public health concern in the Mumbai region during the study period. Young children were the most affected age group. The study data generated will help understand the epidemiology of the disease in the Mumbai region as well as generate information for global influenza surveillance.