Response Levels and Thresholds 2021


NFMAD surveillance and response plan is based on the federal regulations for the state of Colorado Permit  published 3/15/13, hence, on conditions at three levels: Normal season, Emergency planning, and Epidemic.  Five risk factors are analyzed to determine the appropriate response level:


  1.  Environmental condition: snowfall, rainfall, temperature, previous to current season
  2.  Adult mosquito vector species, “abundance”
  3.  Viral test positives on RAMP and/or PCR
  4.  Human cases of mosquito-borne illness, including West Nile and SL Encephalitis
  5. Proximity of detected viral activity in relation to population areas


Each of these risk factors counts as 1 point, with 5 points representing conditions indicative of a high risk of human infection with a mosquito-borne virus.


Level 1: Normal Season, 1.0-2.5

-typical  snowpack, rainfall, average typical temperatures

-mosquito vector species at or below threshold

-Zero viral activity in test pools from trapping

-No human cases


Conduct public education for reducing habitat for breeding at home and personal protection

Conduct mosquito and virus surveillance activities consistent with IPM program

Conduct routine mosquito larval control, as well as continued physical mitigation

Evaluate possible pesticide resistance in vector species, research possible mutations

Ensure adequate emergency response funding

Continue press notices and public information announcements

Level 2: Emergency Planning  2.6-4.0

-Snowpack, rainfall, weather atypical moisture conditions

-mosquito vector species greater than threshold

-One or more positive viral tests of trapped mosquito pools

-One human case in Delta County

-viral activity in close proximity to populated areas


Enhance public education, include signs and symptoms of prevalent illnesses (West Nile, SLE)

Increase surveillance and larval controls

Increase adult surveillance

Increase number of mosquito pools tested for virus

Review, update, and enact selection criteria for adulticide products.  Review candidate pesticides and current product specs for availability and susceptibility of vector species

Conduct localized chemical controls of mosquito adults, up to Phase 3 of Adulticide measures

Contact commercial applicators in anticipation of large scale treatment for adults

Review crisis public communication plan, coordinate with Public Health office.

Level 3: Epidemic,  4.1-5.0

-Snowpack, rainfall, weather,  Atypical, over longer period of time and seasons

-Adult vector populations extremely high, at top of threshold and above

-One or more human illness cases in NFMAD district

-Virus detection on testing in Delta County, regardless of population density


-Conduct full scale media campaign

-Initiate crisis communication plan

-Continue enhanced larval surveillance and control of immature mosquitoes

-Broaden geographic coverage of adult mosquito surveillance and above.

-One or more human illness cases in NFMAD district

-Virus detection on testing in Delta County, regardless of population density

2021 Thresholds for Adult Mosquito Mitigation

Threshold levels are determined based on federal Center for Disease Control (CDC) mandates as of 3/15/13, and the Colorado Department of Public Health rules and regulations for Mosquito Abatement Special Districts during Epidemic designation.  In December of 2012, the CDC reclassified West Nile viral infection as an epidemic, and as a result, NFMAD has significantly altered the operations plan.  Historical data from the years 2008 through 2012 have been compiled and analyzed for each grid map of the district in preparation for the 2013 season.  As of 2019, NFMAD is using the software platform, FieldSeeker, to map and treat the North Fork District, with great success.

Threshold levels are always expressed as a scale of modifiers, meaning that trap data, proximity to denser population areas, calendar of community events, presence of human W. Nile infections in the last year, and other historical data, are all considered when making a treatment decision.  Threshold levels are not simply counting particular species in a trap pool, as much more needs to be considered.

Area with Higher Population Density:

*3-20 Culex species mosquitoes in trap:    Perform  RAMP TEST


*Go to Phase I of Adulticide protocol with targeted, focused      spraying, using backpack or ATV mounted, calibrated equipment


*Go to Phase 1 Adulticide protocol if there are human West Nile cases in area of trapping, and/or a strong, credible suspicion of infected Culex presence based on historical data.

In addition:

*Expand breeding site search, larval and pupal treatment by  .25 mile.

*Evaluate site for possible physical mitigation

*Contact immediate landowners for cooperative mitigation effort and warning of illness possibility

*Re-trap after adulticide application to determine success of   treatment.

*Re-trap again in one week:

if Culex numbers do not drop:    Advance to Phase 2 of Adulticide protocol, and expand search/treatment to .50 mile, in accordance with NPDES and CDC response level requirements.

Area with Lower Population Density:

*15 and above Culex species in trap:

Same modifiers as Area of Higher Population

Total Mosquitoes, non-specified species:

*150 total count and above mosquitoes in trap:

Consider historical evidence of West Nile presence, as well as other modifiers detailed above,  and trigger  Phase 1 Adulticide protocol due to potential for human disease, if non-specified species are acting as an indicator for W. Nile carrying species such as Culex.

For a Scheduled Community Event:

*Increase surveillance, including trapping, 2-3 weeks prior to      event. in a tight perimeter.  Increase all preventive, physical mitigation, larval and pupal product applications, and widen the search for breeding habitat that could cause adult mosquitoes populations to rise in the park or recreational arena hosting the community event.

*Apply Adulticide if indicated and appropriate, according to higher population density modifiers.