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Mosquito Monitoring
mosquito on a fingertip

Mosquito Monitoring for West Nile Virus

Vector Index Log

The vector index tell us the relative risk of West Nile virus transmission. The vector index is based on the:

  • Total number of Culex Pipien and Culex Tarsalis – the species that carry West Nile virus
  • Number of infected mosquitoes across an area. The vector index is calculated by determining the average number of infected mosquitoes collected per trap in an area.
  • Emergency spraying may be recommended when the vector index is at 0.75 or higher.

Mosquito Monitoring 2023

Zone 1Zone 2Zone 3
Week Ending OnVector IndexVector IndexVector Index
June 17 (Week 24)
June 24 (Week 25)
July 1 (Week 26)
July 8 (Week 27)0.004.350.00
July 15 (Week 28)
July 22 (Week 29)3.3116.085.44
July 29 (Week 30)14.1013.8210.74
August 5 (Week 31)5.9514.121.72
August 12 (Week 32)
August 19 (Week 33)0.973.200.81
August 26 (Week 34)1.333.871.86
September 2 (Week 35)0.190.500.40
September 9 (Week 36)
September 18 (Week 37)

NOTE: “—” indicates a single pool was submitted for that zone that tested positive, therefore we were unable to calculate an infection rate or vector index for that zone.

Sentinel Map

Sentinel Zones for mosquito testing

West Nile Data

Contact Us

Vector Control Program

Main: 303-441-1564
Submit a question


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