APPENDIX II-W: Comparing Risk
of WNV:
Comparing Risk of
Virus against Risk of
Adulticiding
Peterson et al. (2006)
compared the risk of
ground-based ultra-low-volume (ULV)
adulticiding against the risk of
virus (WNV). They concluded that
[B]y virtually any
current human-health measure,
the risks from infection by WNV exceed the risks
from exposure to mosquito insecticides.
Therefore, perceptions
that human-health risks
from the insecticides used to control adult mosquitoes
are greater than the risks from WNV currently
cannot be supported by the current
scientific evidence.
We appreciate their elegant analysis of
health risks associated with residential exposure
to ground-based ULV adulticides, and
we concur that such risks are very low.
However, we are concerned that their risk–
risk comparison may be misinterpreted to
indicate that the human health risk associated
with adulticiding is more than offset by
its potential for WNV disease reduction.
Peterson et al. (2006)
did not provide data to
support this. Such a risk–benefit comparison
requires at least two refinements.
First, it needs to take
into account intervention
effectiveness. Although it is not
unreasonable to expect some benefit, it is
unlikely that adulticiding is completely (or
even mostly) effective. Hence, a risk–benefit
comparison would need to address the likely
situation of adulticiding being substantially
< 100% effective, for
example, by reducing
estimates of adulticiding-based benefit by a
factor of 1/x, where x represents the effectiveness
of adulticiding.
Second, it needs to
discount benefit based
on upstream interventions. Adulticiding
often takes place in the context of an integrated
mosquito/WNV management program.
In this situation,
upstream approaches
(e.g., larviciding, personal
protection) discount
the attributable benefit of downstream
interventions (e.g., adulticiding). For
example, use of larviciding and personal
protection, respectively, providing y
and z
effectiveness, reduces the potential benefit of
adulticiding by a factor of 1/[(1 – y) ×
(1 – z)].
Where upstream interventions are used
and are fairly effective and adulticiding
is not
(or
even if it is), adulticiding-attributable
disease reduction may by substantially less
than overall WNV risk. For example, if
larviciding is 75% effective, personal protection
90% effective,
and adulticiding
10% effective, the risk reduction achieved
through adulticiding would be 1/400th of
the overall risk of WNV-related disease;
that is,
Overall risk/{1/[(x) × (1 – y) × (1 – z)]}.
The authors declare they have no competing
financial interests.
Steve Schofield
Martin Tepper
Janick Lalonde
Directorate of Force
Health Protection
Canadian Forces Health Services
Group Headquarters
Department of National Defence
Ottawa, Ontario, Canada
E-mail: schofield.sw@forces.gc.ca
REFERENCE
Peterson RKD, Macedo PA, Davis RS. 2006. A human-health
risk assessment for
used in mosquito management. Environ Health Perspect
114:366–372.
West Nile Virus: Peterson et
al.
Respond
We thank Schofield et al.
for their interest
in our article and for their comments. We
would like to clarify that Peterson et al.
(2006) is simply a screening-level (tier 1)
risk assessment in which we separately and
conservatively examined the residential
human risks from exposure to
virus (WNV) and mosquito adulticides. As
with all screening-level risk assessments,
our assessments were not refined, but they
did reveal the magnitude of risk compared
to relevant end points. As Schofield et al.
point out, our article should not be misinterpreted
to indicate that the health risks
associated with adulticiding are offset by
its potential for WNV reduction. This is
because we did not conduct a risk–benefit
assessment, which was beyond the scope of
our study.
Our article (Peterson et
al. 2006) represents
an initial step in an ongoing multiyear
analysis of risk issues associated with certain
vectorborne diseases and vector management
strategies. We plan to address some of
the issues Schofield et al. raise in subsequent
papers.
The authors declare they have no competing
financial interests.
Robert K.D. Peterson
Paula A. Macedo
Ryan S. Davis
E-mail: bpeterson@montana.edu
REFERENCE
Peterson RKD, Macedo PA, Davis RS. 2006. A human-health
risk assessment for
used in mosquito management. Environ Health Perspect
114:366–372.
Environmental Health Perspectives • VOLUME
114 |
NUMBER 9
| September
2006 A 519
Correspondence
This appendix is copied from:
http://www.ehponline.org/docs/2006/114-9/EHP114pa516PDF.PDF