West Nile Virus & St. Louis Encephalitis End of Year Report, 2022
West Nile virus (WNV) arrived in Arizona in 2003 and is now endemic in Maricopa County. St. Louis encephalitis virus (SLE) is a rare mosquito-borne disease in Maricopa County. Maricopa County
Department of Public Health Division of Epidemiology and Informatics collaborates with the Maricopa County Environmental Services Department Vector Control Division to identify and monitor areas of
WNV and SLE activity. This report describes trends in human infections during 2022.

Year
Total*

Non-neuroinvasive

Neuroinvasive

Hospitalized

Deaths

Sex at Birth
M/F

Median Age
(IQR)

WNV
42**

13 Fever

23 Encephalitis
6 Meningitis/Other Neuro

29 Neuroinvasive
<5 Non-neuroinvasive

<5

28/14

65
(52-73)

SLE
13

<5 Fever

9 Encephalitis
<5 Meningitis

11 Neuroinvasive
<5 Non-neuroinvasive

<5

8/5

60
(39-67)

*Cases are counted in the year in which they are reported to Public Health. Seven WNV cases and one WNV death in the year total had illness onset or incubation in 2021.
**WNV viremic donors who did not become symptomatic (n=2) and those who did not have fever or neurological illness (n=6) are not included in year total.

12

Human Infections of WNV by Month Onset

10
8
6
4

*

2

*

*

Feb

Mar

*

0
Jan
4

Apr

May

Jun

Jul

Aug

Sep

Oct

Human Infections of SLE by Month Onset

*

2

*

*

*

*

†The difference in the mean age of SLE survivors (54 yrs) vs deaths (68 yrs) was not statistically significant (α=0.05).

5 Year Average 180
160
140
120
100
80
60
40
20
0
Nov
Dec

120

5 Year Average

4

*

2

*

*

*

†The difference in the mean age of WNV survivors (61 yrs) vs deaths (82 yrs) was not statistically significant (α=0.05).

*

WNV Deaths 2018–2022

100
80
60
40

*

*

20
0
2018

2019

2020

2021

2022

SLE Deaths 2018–2022

*

*

0

0
Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

2018

*Data are suppressed to prevent identification of cases due to small number (< 5) of cases

2019

2020

2021

2022

West Nile Virus & St. Louis Encephalitis End of Year Report, 2022

Number of Human Cases1

5

4
3
Human

2

Mosquito
1
0

10
9
8
7
6
5
4
3
2
1
0

Number of Mosquito Pools2

Human Infections of WNV1,3,* and WNV Positive Mosquito Pools by MMWR Week

Rates of Human Illness per
100,000 Population
Maricopa County Overall Rate
and Cities§ with Highest Rates

WNV

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
MMWR Week3

PHOENIX

Human Infections of SLE1,3,* and SLE Positive Mosquito Pools by MMWR Week
35
30

4

25

3

20

2

Human

15

Mosquito

10

1

5
0

0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

SCOTTSDALE

Number of Mosquito Pools2

Number of Human Cases1

5

1.2
3

MARICOPA COUNTY
OVERALL

0.95
0

1

2

3

SLE Maricopa County
Overall 0.3‡
‡Due to the low number of cases in 2022, rates of

human SLE illness by cities was not done.

MMWR Week3
1 A human case is an individual infected with WNV or SLE and with a clinically compatible illness.
2 Mosquito pools are a collection of mosquitoes collected by MCESD from a county trap that tested positive for WNV or SLE.
3 Human data are based on date of symptom onset; mosquito data are based on date of mosquito collection.

*Data are suppressed to prevent identification of cases due to small number (< 5) of cases

§Rates for cities with ≥ 100,000 populations and case counts

>4 shown.