[A surveillance system for the study of the circulation of influenza in Madrid during the 1986-1991 quinquennium. The Influenza Surveillance Group of Madrid].

BACKGROUND: The creation of a surveillance system allowing the study of the evolution of the tendency of influenza and act as an alert system for undertaking control measures is necessary due to the great variability characteristic of the circulation of influenza virus. The Madrid Influenza Surveillance Group was therefore designed. The activity carried out during its first five years of existence is evaluated. METHODS: The field work of the Group is based on the clinical study of patients with influenza, among which some are selected for virologic study with the aim to isolate and characterize the circulating virus. The data obtained by the work group itself are used as the dates of the System of Obligatory Disease Declaration and the System of Microbiologic Information as epidemiologic support to define the outbreaks observed. RESULTS: All the virus isolated were similar to those recommended by the World Health Organization for their inclusion in anti-influenza vaccination, with their circulation being largely reproduced throughout Europe. In three of the five seasons studied the type A virus prevailed leading to earlier outbreaks and a greater number of cases than in the two seasons with type B prevalence. CONCLUSIONS: The circulation of the influenza virus in Madrid coincides with that of the rest of Spain at both the maximum peak and relative incidence as well as the type of prevailing virus. The minor circulation detected by the Madrid Group is in concordance with the data provided by the other autonomic communities.