2024 West Nile Virus &
St. Louis Encephalitis Report
WEST NILE VIRUS (WNV) AND ST. LOUIS ENCEPHALITIS (SLE) OVERVIEW
There were 21 WNV cases and zero SLE cases recorded in Maricopa County during 2024. Maricopa
County Department of Public Health Division of Epidemiology and Informatics collaborates with the
Maricopa County Environmental Services Department Vector Control Division (MCESD-VCD) to identify
and monitor areas of activity. The peak for both human cases and mosquito detection was during July.

4

Human cases

8

3

Mosquito pools

6

7
5

2

4
3

1

2
1

0

0
Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Number of Mosquito Pools2

Number of Human Cases1

Human Infections of WNV and WNV Positive Mosquito Pools by MMWR Week

MMWR Weeks by Month3
1 A human case is an individual person infected with WNV and with a clinically compatible illness.
2 Mosquito pools are a collection of mosquitoes collected by MCESD-VCD from a county trap that tested positive for WNV.
3 Human data are based on date of symptom onset; mosquito data are based on date of mosquito collection.

WNV Counts for the 2024 Season
Clinical Syndrome

Demographics

WNV
Total*

Asymptomatic
Donor†

WNV
Fever

Neuroinvasive
Disease

Hospitalized

21

3

6

15

18

Deaths

Gender
M/F

Median Age
(Min, Max)

2

15/6

63 years (24, 93)

* Cases are counted during the year in which they are reported to Public Health.
† WNV viremic blood donors who did not become symptomatic.

Rates of Human WNV Illness per 100,000 Population
MESA

0.8

BUCKEYE

0.9

GILBERT
MARICOPA COUNTY
OVERALL

For additional information:
2.1

0.4

• https://www.maricopa.gov/1746/West-Nile-Virus
• https://www.maricopa.gov/5811/Fight-the-Bite

Numbers included in this report are preliminary and might change.

September 2025