Influenza surveillance.

The main objectives of influenza surveillance are: collection of influenza virus isolates and analysis of their antigenic characteristics so that the most appropriate virus variants can be recommended as constituents of influenza vaccines for use during the next epidemiological season; collection and analysis of information on influenza morbidity and mortality; and earliest possible detection of influenza epidemics. Exact estimates of the specific morbidity and mortality due to influenza are now being carried out in only certain countries. Simple notification of clinical cases and deaths without laboratory confirmation is unsatisfactory and leads to errors in interpretation. The methods used to predict baseline mortality may be inaccurate, resulting in underestimation of mortality associated with influenza virus infection. Comparison of the impact of influenza in different countries is also difficult owing to a variety of methods used for the estimation of mortality and morbidity. Although the laboratory aspects of influenza epidemiology are more uniformly covered worldwide than the statistical aspects, it is still necessary to increase laboratory coverage of some parts of the world and to improve the techniques for the isolation and characterization of not only influenza viruses but also other acute respiratory viruses. The systems and methods for influenza surveillance should be improved and standardized.