Programme for the surveillance of influenza in Portugal: results of the period 1990-1996.

To describe the situation of the influenza in Portugal through the estimates of the incidence rates and the identification of the viral strains implicated on it during the period 1990-1996.,The integrated clinical and laboratory surveillance system for influenza in Portugal is based on the Portuguese sentinel network. Influenza cases are identified by general practitioners (GP) and notified to Division of Epidemiology (DEP) and to National Influenza Centre. Clinical and epidemiological data based on the clinical diagnosis are recorded and incidence rates are computed for the whole country. Throat swabs and blood samples are taken from the patients with influenza and sent to the National Influenza Centre to identify and classify the viral strains implicated.,Lists of patients of the GPs collaborating on "Médicos-Sentinela" network.,In 1990-1991, 1992-1993, and 1994-1995 there was a higher prevalence of influenza B virus and the highest influenza activity occurred in February and March in contrast with 1991-1992, 1993-1994, and 1995-1996 where the highest numbers of influenza cases occurred in November and December, and were associated with influenza A.,During the past six years, 1990-1996, the influenza activity has been moderate in Portugal. From 1990-1996 influenza A and B viruses were prevalent every second year. The prevalence of influenza A was associated with the occurrence of the highest number of influenza cases during December and January and the prevalence of influenza B with the occurrence of the highest number of influenza cases during February and March.