Evaluating strategies for health surveillance. Health event ascertainment at a nuclear facility

The US Department of Energy's Health Surveillance System is a pilot project to design, implement, and evaluate a system of routine morbidity surveillance based on routinely collected occupational medical data at participating Department of Energy facilities. At the Hanford Site, most health events have been ascertained using a 21-day threshold-of-absence criterion. This provisional threshold, established under the assumption that it would capture all important morbidity, has been criticized as potentially omitting morbidity of interest. A review of all health-event absences occurring over a 1-year period revealed that the efficacy of the 21-day threshold varies widely by diagnosis and that absence based eligibility criteria are not useful for all morbidity of interest. Future development will require supplementation of health-event ascertainment by other, diagnosis-based criteria to ensure completeness of ascertainment.