Epidemiological and virological influenza survey in Dakar, Senegal: 1996-1998

An influenza survey was conducted in seven sentinel sites in Dakar, Senegal from June 1996 to December 1998. Throat or nasal swab cultures were random ly collected from 804 patients suffering from influenza-like symptoms. Infl uenza viruses were isolated at a similar proportion in adults and in childr en (P = 0.29). Strains of influenza B viruses were isolated from sporadic c ases in 1997, whereas type A virus was associated with an isolated peak. Pr oportions of influenza virus isolation varied from 17.5% to 40.0% between 1 996 and 1998 during the peak period (July/September) of acute respiratory i nfection in Dakar. Rainfall, humidity, and temperatures rose during the sam e period. Influenza in Dakar seems to be an-all-age groups respiratory infe ction characterized by high transmission during the hot and rainy season. T he antigenic similarity of the A(H3N2) and B viruses to those circulating e lsewhere in the world at the same time was confirmed. However, the A(H1N1) strains were found to be more closely related to an Asiatic strain which ha d not been isolated outside Asia previously. Consequently, the strain close to the A(H1N1)/Wuhan/371/95 strain isolated in Dakar was included in the c omposition of the 1998/1999 influenza vaccine. This reinforces the importan ce of setting up a national influenza control strategy in tropical regions.