Defining 'surveillance' in drug safety.

The concept of surveillance in pharmacovigilance and pharmacoepidemiology has evolved from the concept of surveillance in epidemiology, particularly of infectious diseases. We have surveyed the etymology, usages, and previous definitions of 'surveillance' and its modifiers, such as 'active' and 'passive'. The following essential definitional features of surveillance emerge: (i) surveillance and monitoring are different--surveillance involves populations, while monitoring involves individuals; (ii) surveillance can be performed repeatedly and at any time during the lifetime of a medicinal product or device; (iii) although itself non-interventional, it can adduce any types of evidence (interventional, observational, or anecdotal, potentially at different times); (iv) it encompasses data collection, management, analysis, and interpretation; (v) it includes actions to be taken after signal detection, including initial evaluation and communication; and (vi) it should contribute to the classification of adverse reactions and their prevention or mitigation and/or to the harnessing of beneficial effects. We conclude that qualifiers add ambiguity and uncertainty without enhancing the idea of surveillance. We propose the following definition of surveillance of health-care products, which embraces all the surveyed ideas and reflects real-world pharmacovigilance processes: 'a form of non-interventional public health research, consisting of a set of processes for the continued systematic collection, compilation, interrogation, analysis, and interpretation of data on benefits and harms (including relevant spontaneous reports, electronic medical records, and experimental data).' As a codicil, we note that the purposes of surveillance are to identify, evaluate, understand, and communicate previously unknown effects of health-care products, or new aspects of known effects, in order to harness such effects (if beneficial) or prevent or mitigate them (if harmful).