Experience of European collaboration in influenza surveillance in the winter of 1993-1994

Background The spread of influenza is of major public health concern. Surveillance programmes exist in many countries. We here describe an international collaboration sharing information from Belgium, France, The Netherlands, Portugal and the United Kingdom during the influenza A(H3N2) epidemic occurring in Europe at the end of 1993. Methods Procedures for clinical and virological surveillance in each country are described. National data were assembled at one point in each country and entered on a computerized data base in Paris for integration. A background rate of influenza was identified from the two previous winters (1991-1992 and 1992-1993) using the measurement of incidence routinely used in each country. The epidemic in late 1993 was described in relation to the background rate. The proportion of cases in each of three age groups (0-14, 15-44 and 65 years and over) was compared in different stages of the epidemic. Results All national systems effectively identified the onset and monitored the course of the epidemic. Standardization of incidence data gave only limited assistance to the interpretation of the data. The distribution of cases by age group was similar in the early and late periods of the epidemic in all countries. increased clinical incidence was matched by a simultaneous increase in positive virus identifications in all countries except England and Wales, where the interval between the week of peak clinical incidence and of peak virus reports is mainly due to a reporting procedure based on date of report received at the Central Public Health Laboratory rather than date of specimen capture. Conclusion An international early warning system for monitoring influenza has been established.