West Nile Virus and St. Louis Encephalitis
2017 End of Year Report
West Nile virus (WNV) arrived in Arizona in 2003 and is now endemic in Maricopa County, and St. Louis encephalitis virus (SLEV) is a rare
mosquito-borne disease in Maricopa County. The Maricopa County Department of Public Health (MCDPH) Office of Epidemiology
collaborates with the Maricopa County Environmental Services Department (MCESD) Office of Vector Control to identify and monitor areas
of WNV and SLE activity. This report describes human infections during 2017.
Please visit http://www.maricopa.gov/1608/Mosquito-Related-Diseases for more information about mosquito-related diseases.

WNV

SLEV

Year
Total

Non-neuroinvasive

Neuroinvasive

Hospitalized

Deaths

Gender

Median
Age
(Min, Max)

93*

8 Fever
3 Other Clinical
1 Unknown

43 Encephalitis
31 Meningitis
7 Other

73 Neuroinvasive

6

53 male
40 female

62
(1, 92)

68 White, Non-Hispanic
1 Black, Non-Hispanic
2 Asian/Pacific Islander
11 Hispanic or Latino
1 Other, Non-Hispanic
10 Unknown

3 Fever

1 Encephalitis
1 Meningitis

2 Neuroinvasive

0

4 male
1 female

49
(43, 63)

2 White, Non-Hispanic
1 Black, Non-Hispanic
2 Unknown

5

2 Non-neuroinvasive

Race/Ethnicity

*Viremic donors who did not become symptomatic (10) are not included in year total

WNV Mortality Description 2017

Human Cases of WNV and SLEV in Maricopa, 2013-2017
Confirmed
Deaths
6

100

Clinical Presentation
4 Encephalitis
2 Meningitis

Gender
M/F
2/4

Race/Ethnicity
White, Not
Hispanic
1
Hispanic
5

80

Mean age of West Nile Virus survivors (57 years) versus deaths (81 years) was
statistically significant for 2017 (α=0.05).

70
60
50

WNV Cases in Humans and WNV Positive Mosquito Pools in
Maricopa County, 2017

20

25

10
0
2013

2014

West Nile Virus

2015

2016

2017

St. Louiuis Encephalitis Virus

Rates of Human WNV in Maricopa County By
City, 2017
MESA
GILBERT
SCOTTSDALE
CHANDLER
SURPRISE
TEMPE
PEORIA
PHOENIX
GLENDALE
Total

4.68
4.41
4.26
2.48
2.35
2.29
2.25
1.61

120
100

WNV Human
Cases (n=93)

20

80

Mosquito
Pools (n=228)

15

60

10

40

5

20

0

0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

SLEV Cases in Humans and SLEV Positive Mosquito Pools in
Maricopa County, 2017
30
120
25

100
SLE Human Cases
(n=5)

20
15

60

SLE Mosquito
Pools (n=160)

10
5

80

40

3

1

1

0

0.42
2.27

1 Population statistics for each city were obtained from United States Census
Bureau 2016 Population Estimates
2 Rate per 100,000 population = (N/population) * 100,000
3 Rates for cities with ≥ 100,000 populations shown
*Total includes cities displayed in figure, as well as other cities and
unincorporated areas with populations <100,000

Number of Mosquito Pools2

30

Number of Human Cases

30

20
0

Number of Mosquito Pools2

40

Number of Human Cases

Number of Human Cases

90

Median
Age (Min,
Max)
83
(72, 91)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month3
2 Mosquito pools are a collection of mosquitoes collected by

MCDES from a county trap and tested positive for WNV or SLEV
3 Human cases are based on date of symptom onset, mosquito
data are based on date of mosquito collection