West Nile Virus
2013 End of Year Report
West Nile virus (WNV) arrived in Arizona in 2003 and is now endemic in Maricopa County. The Maricopa County Department
of Public Health (MCDPH) Office of Epidemiology collaborates with the Maricopa County Department of Environmental
Services (MCDES) Office of Vector Control to identify and monitor areas of WNV activity. This report describes trends in
human infections during 2013. Please visit http://www.maricopa.gov/wnv/ for more information about WNV.
Characteristics of Human WNV Infections: Maricopa County, 2013
Year
Total*

Non-neuroinvasive

52

8
1

Neuroinvasive

=Fever
=Fever in donor

25
16
2

=Encephalitis
=Meningitis
=Paralysis

Hospitalized
43
3

Deaths

Gender
M/F

6

29/23

=Neuroinvasive
=Non-neuroinvasive

Demographics
Median Age
(Range)
Race/Ethnicity
58
(17-93)

40
6
1
1
4

=White, Non-Hispanic
=Hispanic or Latino
=Black, Non-Hispanic
=Other, Non-Hispanic
=Unknown

*Viremic donors who do not become symptomatic (3) are not included in year total

WNV Cases in Humans and WNV Positive Mosquito Pools in
Maricopa County by Month, 2013

45
Number of Human Cases1

Number of Human Cases

40

2012 (n=88)

35

2011 (n=45)
2010 (n=115)

30

2009 (n=19)

25

60

18

2013 (n=52)

2008 (n=91)

20

Human Cases
(n=52)
Mosquito Pools
(n=180)

16
14
12

30

8
6

20

4

10

2

15

0

0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month3

5

1

A human case is an individual infected with WNV and with a clinically compatible
illness
2
Mosquito pools are a collection of mosquitoes collected by MCDES from a county trap
and tested positive for WNV
3
Human data are based on date of symptom onset, mosquito data are based on date of
mosquito collection

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

WNV Deaths in Maricopa County, 2008-2013

Chandler

3.21

Gilbert

1.74

Glendale

0.43

Mesa

1.31

Phoenix

0.93

Scottsdale

4.41

Surprise

Number of Deaths

Rates of Human WNV Cases in Maricopa County
By City, 2013

City1,3

40

10

10

15

12

10
6
2
0

0
2008

1.00

2010

2011

2012

2013

WNV Mortality Description 2013

1.30
0.00

2009

Year

1.19

Total*

6

4

5

1.62

Tempe

1

50

Number of Mosquito Pools2

Human Cases of WNV in Maricopa County by Month of
Onset, 2008-2013

2.00

3.00

Rates per

100,0002

4.00

5.00

Population statistics for each city were obtained from United States Census Bureau
2013 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

Confirmed
Deaths
6

5
1

Clinical
Presentation

Median
Age
(Range)

=Encephalitis
=Paralysis

77
(66-89)

Gender
M/F
3/3

Race/Ethnicity
6

=White,
Non-Hispanic or
Latino

Mean age of West Nile Virus survivors (53 years) versus deaths (77 years) was statistically
significant for 2013 (α=0.05).