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West Nile Virus - Phased Response Printer Friendly Version

Suggested Guidelines for Phased Response to West Nile Virus Surveillance Data

Risk category
Probability of human outbreak
Recommended response*
None Off-season; adult vectors inactive; climate unsuitable. Develop WN virus response plan. Secure surveillance and control resources necessary to enable emergency response. Initiate community outreach and public education programs.
Remote Spring, summer or fall; areas unlikely to have WN virus epizootic in 2001 based on lack of previous or current WN virus activity in the region. Response as in category 0, plus: Conduct entomologic survey (inventory and map mosquito populations; see AMCA and other manuals for guidance); community outreach and public education; avian mortality, human encephalitis/meningitis and equine surveillance.
Remote Spring, summer or fall; areas anticipating WN virus epizootic in 2001 based on previous or current surveillance findings indicating WN virus epizootic activity in the area. Response as in category 1a, plus: Source reduction; use larvicides at specific sources identified by entomologic survey and targeted at likely amplifying and bridge vector and virus surveillance; public education emphasizing source reduction.
Low Spring, summer or fall; area with initial, sporadic or limited WN virus epizootic activity in birds and/or mosquitoes. Response as in category 1b, plus: Increase larval control and source reduction and public education emphasizing personal protection measures, particularly among the elderly. Enhance human surveillance and activities to further quantify epizootic activity (e.g., mosquito trapping and testing). Consider focal or targeted adult mosquito control if surveillance indicates likely potential for human risk to increase.
Moderate Spring, summer or fall; areas with initial confirmation of WN virus in a horse and/or a human, or moderate WN virus activity in birds and/or mosquitoes. Response as in category 2, plus: Strongly consider adult mosquito control if surveillance indicates likely potential for human risk to persist or increase.
High Spring, summer or fall; quantitative measures indicating WN virus epizootic activity at a level suggesting high risk of human infection (for example, high dead bird densities, high mosquito infection rates, multiple positive mosquito species, horse or mammal cases indicating escalating epizootic transmission, or a human case and high levels of epizootic activity) and abundant adult vectors. Responses as in category 3, plus: Expand public information program to include TV, radio, and newspapers (use of repellants, personal protection, and continued source reduction, risk communication about mosquito control); initiate or continue active surveillance for human cases; implement adult mosquito control program targeted at areas of potential human risk.
Outbreak in progress Multiple confirmed cases in humans; conditions favoring continued transmission to humans (see level 3). Response as in category 4, plus: Implement or intensify emergency adult mosquito control program, enhanced risk communication about adult mosquito control, monitor efficacy of spraying on target mosquito populations. If outbreak is widespread and covers multiple jurisdictions, consider wide-spread aerial spraying as per the WN virus Emergency Contingency Plan.
Ref: Page 38 of Epidemic/Epizootic West Nile Virus in the United States: Revised Guidelines for Surveillance, Prevention and Control
*Local and regional characteristics may alter the risk level at which specific actions must be taken.



This page was last modified onMonday, July 26, 2010 9:21