A sentinel surveillance system is used when high-quality data are needed about a particular disease that cannot be obtained through a passive system. Selected reporting units, with a high probability of seeing cases of the disease in question, good laboratory facilities and experienced well-qualified staff, identify and notify on certain diseases. Whereas most passive surveillance systems receive data from as many health workers or health facilities as possible, a sentinel system deliberately involves only a limited network of carefully selected reporting sites. For example, a network of large hospitals might be used to collect high-quality data on various diseases and their causative organisms, such as invasive bacterial disease caused by Haemophilus influenzae type b, meningococcus or pneumococcus.
Data collected in a well-designed sentinel system can be used to signal trends, identify outbreaks and monitor the burden of disease in a community, providing a rapid, economical alternative to other surveillance methods. Because sentinel surveillance is conducted only in selected locations, however, it may not be as effective for detecting rare diseases or diseases that occur outside the catchment areas of the sentinel sites.
The following criteria should be considered in selecting a sentinel health facility (usually a general or infectious disease hospital) :
It should be willing to participate.
It serves a relatively large population that has easy access to it.
It has medical staff sufficiently specialized to diagnoze, treat and report cases of the disease under surveillance.
It has a high-quality diagnostic laboratory.