General considerations for surveillance during Phase 3
In pursuing these objectives, the following considerations underpin the Phase 3 surveillance strategy:
• The strategy observes the practical requirement to balance the intensity and cost of surveillance against
acceptable risks. Until the end of the outbreak (as described above), a surveillance with high sensitivity
must be maintained i.e. activities that have a high chance of detecting new EVD cases and deaths,
especially in areas of recent EVD activity, recognizing that a significant number of suspects will be
found to have no EVD on further investigation.
• Once the outbreak has been declared over, and as the risk of EVD subsides, a sensitive surveillance
strategy will be replaced by one that is more specific i.e. less labour intensive and less costly, allowing
the possibility that a single new case will not be detected immediately, but maintaining a high probability
of detecting a cluster of cases or a community death.