West Nile Virus Response Plan

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APPENDIX A
DECISION MATRIX
West Nile Virus Surveillance
Agency Response Triggering Thresholds

Tier I Counties*: Tier I Actions
Conduct enhanced passive human surveillance
Conduct passive bird surveillance
Conduct Level 1 education campaign
Consider larval mosquito surveillance
Consider adult mosquito surveillance, selected submission of known vector species
Consider local environmental assessments
Consider local disease risk assessments
Pursue state aid review/approval
Tier II Counties*: Tier II Actions = Tier I Actions, plus
Conduct active human surveillance (only counties with historical evidence)
Conduct active bird surveillance
Conduct enhanced Level 1 education campaign
Conduct larval mosquito surveillance and control
Conduct larval habitat source reduction programs
Conduct adult mosquito surveillance, submission of known and suspected vector species
Conduct local environmental assessments
Conduct local disease risk assessments

*Tier II counties: Nassau, Suffolk, Rockland, Westchester, Putnam, Orange, and New York City
Tier I counties: All others

LHU Response Activities Based on Current Surveillance Data
Current Surveillance Data1 Initial LHU Tier Response
1) Culex pipiens larvae detected I - No historical evidence Same as Tier I Actions above, plus
Enhance Level I education campaign
Initiate larval habitat source reduction programs
Map (GIS) larval breeding sites
II - Historical evidence Same as Tier II Actions above, plus
Enhance larval habitat source reduction programs
Map (GIS) larval breeding sites
2) Culex pipiens adults detected I - No historical evidence All of above Tier I Actions, plus
Enhance larval habitat source reduction programs
Consider enhanced mosquito surveillance (gravid traps)
Map (GIS) adult trapping locations
Consider larval mosquito control
II - Historical evidence All of above Tier II Action, plus
Conduct enhanced adult mosquito surveillance activities
Conduct larval mosquito control
Map (GIS) adult trapping locations
3) Single WNV infected mosquito pool I - No historical evidence All of above Tier I Action, plus
Initiate active human surveillance
Initiate active bird surveillance
Initiate Level 2 education campaign
Enhance larval source reduction programs
Initiate larval control programs
Consider ground-based ULV adult mosquito control2
II - Historical evidence All of above Tier II Action, plus
Initiate Level 2 education campaign
Conduct ground-based ULV adult mosquito control2
4) WNV infected mosquito pools in multiple locations I - No historical evidence All of above Tier I Actions, plus
Initiate ground-based ULV adult mosquito control2
Consider aerial adult mosquito control2
II - Historical evidence All of above Tier II Actions, plus
Consider aerial ULV adult mosquito control2
5) Single WNV positive bird3 I - No historical evidence Same as Culex pipiens adults detected, plus
Expand current adult mosquito surveillance with lab testing to include site with dead bird
Initiate Level 2 education campaign
Initiate active human surveillance
Initiate active bird surveillance
II - Historical evidence Same as Culex pipiens adults detected, plus
Initiate Level 2 education campaign
Initiate active human surveillance
Initiate active bird surveillance
6) Multiple WNV positive birds3 I - No historical evidence Same as single positive bird, plus
Consider ground-based or aerial adult mosquito control2
II - Historical evidence Same as single positive bird, plus
Enhanced mosquito surveillance if not done already
Conduct ground-based ULV adult mosquito control2
Consider aerial control of adult mosquitoes2
7) WNV positive horse3 I - No historical evidence Same as multiple WNV positive birds, plus
Initiate active veterinary surveillance
II - Historical evidence Same as multiple WNV positive birds, plus
Initiate active veterinary surveillance
8) Human WNV case Either Tier All of the above, plus
Initiate Level 3 educational campaign
Conduct larval surveillance and control2Conduct adult surveillance and consider aerial control2
9) Multiple Human WN cases Either Tier Same as above single human case, plus
Initiate Level 3 or 4 educational campaign
Consider aerial control of adult mosquitoes2

Footnotes

  1. Each surveillance factor adds to the previous action level.
  2. In general, ground application of pesticides should be the preferred method of control. Aerial application of insecticides for adult mosquito control should be considered only in Tier IV circumstances and only after careful consideration of the risk to human health by taking into account multiple factors, including the size of the vector population, the vectors' physiologic age, the density and proximity of human populations, the time of year, weather conditions, physiography of and accessibility to the area where the vector is located, rapidity of response required as determined by the seriousness of the public health threat, and the likelihood that vectors in nearby areas not subject to control measures will migrate from the area if not subject to control. Aerial spraying should be limited to the immediate area where the vector population has been documented to exist through vector surveillance and to adjacent areas considered at risk for imminent disease transmission.
  3. Evidence of recent infection, i.e. virus isolation, IgM antibody or seroconversion. IgG antibody alone does not provide evidence of recent infection.

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Revised: May 2000

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