Mosquito-Borne Disease Surveillance

Maricopa County Environmental Services Department has an extensive mosquito-trapping program that enables staff to identify areas where there is mosquito activity and to detect any mosquito-borne diseases. 

Various types of mosquito traps are set up throughout the county that collect mosquitoes for testing. These mosquitoes are pooled together, by species, into groups of 1-50 mosquitoes. This collection of mosquitoes is called a mosquito pool. The female mosquitoes are separated and are then processed and tested for West Nile virus (WNV) and Saint Louis Encephalitis (SLE). Traps with pools or samples that test positive for WNV and SLE are listed in graphics below.

West Nile Virus Statistics

Category2010201120122013201420152016201720182019
 
2020
 
2021
 
2022
Positive Horses Reported to ESD0300310 0 2 1 1 4 00
0
0
Positive Mosquito Samples18691681392189795228138 417 1076462157
48
16

Statistics provided by the Environmental Services Department (ESD) 

*Maricopa County Environmental Services' PCR testing results as of June 6, 2025.

St. Louis Encephalitis Statistics


Category20152016 2017 2018 2019
 
 2020 20212022
 
2023
Positive Mosquito Samples600160106 2131524425342
5
10
         



Statistics provided by Environmental Services.

* MCESD's PCR testing results as of June 6, 2025.

Public Health Statistics on Human Cases

Find current human case counts and historical case counts of mosquito-borne diseases among Maricopa County residents.

June 2025

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  1. Environmental Services Department

    Physical Address
    301 W Jefferson St
    Suite 170
    Phoenix, AZ 85003

    Fax 602-506-5141

  1. Public Health


    Physical Address
    4041 N. Central Ave.
    Suite 1400
    Phoenix, AZ 85012

    Fax 602-506-6885