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


Category
2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
 
2020
 
2021*
 
Positive Dead Birds 1 0 0 2 0 0 0 0  0  1  0  0  0
Positive Horses 0 0 3 0 0 3 1 0  0  2  1  1  4
Positive Mosquito Samples
51
186
9
168
139
218
97
95 228 138  417  108 748

Statistics provided by Environmental Services.
*Maricopa County Environmental Services Department's PCR testing results, as of October 22, 2021.

St. Louis Encephalitis Statistics


Category
2015 2016  2017  2018  2019
 
 2020
 2021*
Positive Mosquito Samples 60 0 160 106  213 152 30
               

Statistics provided by Environmental Services.
* MCESD's PCR testing results, as of October 22, 2021.

Public Health Statistics on Human Cases

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

  1. Environmental Services Department

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

    Phone: 602-506-6616
    Fax: 602-506-5141

  1. Public Health


    Phone: 602-506-6900
    Fax: 602-506-6885