Zoonoses Program, New York State Department of Health, Albany, New York 11237, USA
Address for correspondence: Millicent Eidson, Zoonoses Program, New York State Department of Health, Albany, New York 12237. Voice: 518-474-3186; fax: 518-473-6590.
mxe04{at}health.state.ny.us
Passive surveillance is usually viewed as less efficient for
case ascertainment than active surveillance. However, for diseases
with nonhuman animal reservoirs, active surveillance can be
like looking for a needle in a haystack and may be prohibitively
expensive. Fortunately for surveillance of West Nile virus (WNV)
in the northeast US, the dead crows have served as "neon needles
in a haystack"—indicators of viral activity that call
attention to themselves. In 2000, laboratory testing of dead
birds, including all species, birds found singly, with signs
of trauma, or no compatible pathology, provided the first confirmation
of viral activity in most areas. The surveillance factor most
closely associated with the number of human cases was the dead
crow density. In 2001, dead crow densities will be used as an
additional index for monitoring human risk and need for prevention
and control activities. If there are few crows in an area, if
their case-fatality rate is reduced, or if there is public complacency
about reporting dead crow sightings, this passive surveillance
indicator may not be helpful in identifying areas likely to
have occasional human cases or an outbreak.
