Influenza surveillance: experiences from establishing a sentinel surveillance system in Germany.

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Abstract
OBJECTIVES--Before and during peak influenza periods there is increased morbidity from other respiratory tract disorders. Sentinel networks of primary care physicians can be very effective in the early detection of influenza epidemics and the German network, the Arbeitsgemeinschaft Influenza (AGI), began its work in this area in 1992. METHODS--Data are transmitted weekly from the doctor's computer via Btx to a central computer. The numerator is the weekly number of acute respiratory infections (ARI) in five age groups and the denominator is the weekly number of patient consultations. Data on hospitalisation, mortality, and days of sick leave from work or school are also collected. Swabs for influenza specimens are collected in 30 physicians' offices each Monday and sent to three reference centres. FINDINGS--During the last recording period, from week 46 1993 to week 15 1994, 411 physicians' offices participated in the network. For 16 to 22 weeks, more than 60% of the participants transmitted data. During both the 1992-93 and 1993-94 influenza seasons, peaks were observed in the rate of ARI. There was a corresponding increase in sick leave from work and school. Rates for hospitalisation and deaths due to influenza showed no peaks during either season. CONCLUSIONS--Although the German sentinel network for influenza experienced some technical problems in the first year, it was possible to solve these. Reporting rates were very satisfactory in the second year. The network will now be expanded to include 750 physicians in order to receive 600 weekly reports and obtain a solid baseline for an early warning system.