In many European countries, there is a considerable lack of useable health-related data from the ambulatory care sector. Thus, primary health care research - i. e. contact-based epidemiology of ambulatory care - has been of increasing importance for the last decade. Through ongoing health care research, the frequency and distribution of health problems which either have not yet or never will have contact with the hospital sector can be monitored.

Sentinel practice networks, also referred to as practice research networks, have become an important epidemiological instrument for morbidity surveillance in many countries of the western world. In such networks, office-based physicians cooperate on a (mostly) non-monetary basis in monitoring defined events among their patients (e. g. influenza, mumps, asthma attacks) in a standardized way. Sentinel systems can also be used as an approach to the served population for various types of epidemiological studies. The unique contribution of such networks is the ability to obtain data on pre-clinical health-related events continuously and directly from the ambulatory health care system. After adequate analysis, these data may indicate spatial and temporal trends in the frequency and distribution of defined health events and give information on patient management, or etiologic hypotheses can be generated or tested. Nevertheless, many methodological problems inherent to this approach have to be solved in order to obtain valid information by sentinel systems [4, 5]. Some of these obstacles are intrinsic to the health care system itself, others are specific to contact-based epidemiology by means of sentinel practice networks.

Schlaud M, Schwartz FW. Foreword. J Epidemiol Community Health 1998; 52 (Suppl 1): 1S.