We conducted population-based surveillance for influenza virus among children under age 5 years in the Kamalapur neighbourhood of Dhaka. Between April 2004 and November 2005, 14% of children with acute infectious respiratory illness had influenza virus isolated from their respiratory secretions. The incidence of influenza virus infection was 84.5 episodes/1000 children/year. 58% of isolates were influenza A (H3N2, H1N1) and 42% are influenza B (Shanghai and Hong Kong). Both strains of Influenza A virus and both strains of Influenza B virus that are circulating within Asia are circulating within Bangladesh.

Although influenza virus was isolated more commonly between April and September, influenza transmission occurred year round. This may be important globally, as most temperate zones have peak transmissions during the late fall to winter months (November-March). Populations like Bangladesh may provide a supplemental reservoir, helping to keep the virus in circulation with opportunities for mutation until the following season. If these data are confirmed in other settings it suggests that influenza vaccination in Bangladesh would need to occur early in the year to prevent the highincidence season.

These are data from children under age 5 years. The impact of influenza infection on adult health in Bangladesh is unknown, but the high incidence among children and the multiple circulating strains suggest that influenza virus may also be an important respiratory pathogen in adults. Further research could clarify the magnitude of the problem and permit evaluation of the cost-effectiveness of routine influenza vaccination.

Health and Science Bulletin, 4(1):1-5