A new influenza surveillance system in France: the Ile-de-France "GROG". 1. Principles and methodology.

The aims of influenza surveillance have changed over the years. The early detection of epidemics is essential for practical decisions on vaccine development, strategy of vaccine prophylaxis, chemoprophylaxis or chemotherapy. A new surveillance system is presented which combines the classical specific data related to the isolations, direct detection of virus as well as serological findings, with non-specific indices. The rationale for definition and elaboration of such indices is discussed: selected parameters deal with medical activity of a panel of sentinel doctors (general practitioners and pediatricians), notifications of diagnosed acute respiratory viral infections, measure of emergency doctors activity, absence from work (as seen by physicians, insurance agencies or industrial personnel), selected drug prescription and consumption, hospital admissions. The sentinel physicians also cooperate in taking samples from cases, thereby extending the field of specific surveillance since they have contact with standard cases of the disease and not only hospitalized patients. A weekly comparison of time variations of specific and non-specific indices should permit a reliable evaluation of the epidemic situation and therefore be of great help for practical decisions. The system has operated since 1984, and the initial hypothesis of the sensitivity of some of the indices has already been verified.