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

*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.

Revised: May 2000

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