A study of reasons for an increase in acute respiratory tract infections reported by influenza sentinel practices in Germany.

The influenza sentinel and early warning system of the working group on influenza (AGI) comprises more than 600 general practitioners and paediatricians nationwide. The observations made by national influenza monitoring systems rely on parameters that differ between countries. The definition of the numerators and denominators used depends to an important extent on the national health care systems, and considerable differences between the national monitoring systems have to be expected. Consequently the validity and reliability of recorded data as well as the indicative value of certain observations have to be checked for each system. The reasons for an increase in acute respiratory infections relative to total practice contacts, as well as the number of persons who are unable to work, were investigated by telephone interviews with the reporting physicians. Reasons for such increases given by the physician included increases in morbidity in the population but to a considerable extent "organisational" reasons, not linked to an increase in morbidity were identified. Many of those "organisational" reasons seemed to be relevant in health care systems that allow the patients a free choice of the contacted physician. The telephone interview was helpful for interpretation of the data and the detection of primary local outbreaks.