|
Risk category
|
Probability of human outbreak
|
Definition
|
Recommended response*
|
|
0
|
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. |
|
1a
|
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. |
|
1b
|
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. |
|
2
|
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. |
|
3
|
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. |
|
4
|
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. |
|
5
|
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. |
