West Nile Virus 2015 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 in 2015 during a concurrent outbreak of WNV and St. Louis encephalitis (SLE).
Please visit http://www.maricopa.gov/publichealth/Diseases/mosquito/ for more information about WNV.
Characteristics of Human WNV Infections: Maricopa County, 2015
Year
Total*
†

Non-neuroinvasive†
23
3

62

=Fever
=Fever in donor

Neuroinvasive
15
21

=Encephalitis
=Meningitis

Hospitalized
36
10

Deaths

Gender
M/F

2

35/27

=Neuroinvasive
=Non-neuroinvasive

Demographics
Median Age
(Range)
Race/Ethnicity
56
(21-89)

44
7
2
2
7

*Viremic donors who do not become symptomatic (6) and cases of
unspecified flavivirus are not included in year total

=White, Non-Hispanic
=Hispanic or Latino
=Native American
=Other, Non-Hispanic
=Unknown

Human Cases of WNV in Maricopa County by Month of

WNV Cases in Humans and WNV Positive Mosquito Pools in

Onset, 2011-2015

Maricopa County by Month, 2015

Number of Human Cases

30

2014 (n=93)
2013 (n=52)

25

2012 (n=88)

20

2011 (n=45)

15

Human Cases
(n=62)

25

Number of Human Cases1

2015 (n=62)

60

20

50
40

Mosquito Pools
(n=97)

15

30

10

20

5

10

0

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

10

Number of Mosquito Pools2

30

35

Month3

5

1

A human case is an individual infected with WNV and with a clinically compatible illness
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
2

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

TOTAL
Gilbert
Scottsdale
Tempe
Mesa
Glendale
Chandler
Surprise
Peoria
Phoenix

Number of Deaths

City1,3

Rates of Human WNV Cases in Maricopa County
By City, 2015
1.52
4.18
3.04
2.31
2.15

WNV Deaths in Maricopa County, 2011-2015

15

12

10

2

2

0
2011

1.97

2012

2013

2014

2015

Year

1.58
1.20

WNV Mortality Description 2015

0.52

1.00

6

4

5

2.11

0.00

2.00

3.00

4.00

5.00

Rates per 100,0002
1

mosquito collection

Population statistics for each city were obtained from United States Census Bureau
2014 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
2

Clinical
Presentation
2

=Encephalitis

Median
Age
(Range)
74.5
(73-76)

Gender
M/F
1/1

Race/Ethnicity
2

=White, NonHispanic or Latino

There was no statistically significant difference in age in survivors versus deaths