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West Nile Virus Activity in California in 2004

Division of Communicable Disease ControlCalifornia Department of Health Services

WNV Team at DHS• VBDS

– Vicki Kramer– Stan Husted– Al Hom– Ryan Carney– Kerry Padgett– Lauren Marcus– Anne Kjemtrup– Mark Novak– Renjie Hu

• DIS– Jon Rosenberg

• VPHS– Ben Sun– Jason Stull

• VRDL– Carol Glaser– Cynthia Jean– Cindi Cossen– Liz Baylis

• OPA– Rosanna Westmoreland

Collaborators

• Local Health Departments

• Local Public Health Laboratories

• Environmental Health Departments

Humans 828 (27 deaths)

Equines 536

Dead birds 3,232

Mosquito pools 1,136

Sentinel chickens 809

WNV in California, 2004

Data as of 1/27/05

WNV in California, 2003

Equine Case

Human Case

32 10,111

70 31,227

96 1,769

POS N

February 2004

1 county

Humans, onset / reported 0 Horses, onset / reported 0 Dead birds 1Mosquito pools 0Sentinel chickens 0

WNV activity (number of human cases with known onset date)

WNV activity (no human cases)

March 2004

1 county

Humans, onset / reported 0Horses, onset / reported 0Dead birds 2Mosquito pools 0Sentinel chickens 0

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

April 2004

5 counties

Humans, onset / reported 0Horses, onset / reported 0Dead birds 14Mosquito pools 8Sentinel chickens 0

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

May 2004

6 counties

5

Humans, onset / reported 5 / 0Horses, onset / reported 0Dead birds 391Mosquito pools 41Sentinel chickens 6

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

June 2004

11 counties

28

8

10

2

WNV activity (number of human cases with known onset date)

Humans, onset / reported 50 / 4 Horses, onset / reported 15 / 4Dead birds 874Mosquito pools 180Sentinel chickens 113

2WNV activity (no human cases)

July 15, 2004

21 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 111 / 24 Horses, onset / reported 40 / 26Dead birds 1073Mosquito pools 364Sentinel chickens 166

1

1

60

16

28

2

3

July 31, 2004

39 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 261 / 54 Horses, onset / reported 94 / 44Dead birds 1447Mosquito pools 526Sentinel chickens 257

2

1

120

40

79

5

1

1

1

1

9

1

August 15, 2004

52 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 422 / 168 Horses, onset / reported 162 / 87Dead birds 1942Mosquito pools 688Sentinel chickens 326

3

1

160

57157

14

2

1

1

1

23

1

1

August 31, 2004

56 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 529 / 430 Horses, onset / reported 264 / 199Dead birds 2440Mosquito pools 858Sentinel chickens 474

4

1

174

68212

30

2

1

1

1

29

1

1

1

1

1

1

September, 2004

58 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 621 / 654 Horses, onset / reported 387 / 419Dead birds 3030Mosquito pools 1091Sentinel chickens 715

5

1

180

71249

52

3

1

5

1

41

1

1

1

1

2

1 1

12

1

October, 2004

58 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 633 / 790 Horses, onset / reported 326 / 529 Dead birds 3192Mosquito pools 1135Sentinel chickens 779

5

1

180

72251

57

3

1

5

2

41

1

2

1

1

2

1 1

32

1

November, 2004

58 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 633 / 817 Horses, onset / reported 426 / 536Dead birds 3225Mosquito pools 1136Sentinel chickens 802

5

1

180

72251

57

3

1

5

2

41

1

2

1

1

2

1 1

32

1

December, 2004

58 counties

WNV activity (no human cases)

WNV activity (number of human cases with known onset date)

Humans, onset / reported 633 / 828 Horses, onset / reported 426 / 536Dead birds 3232Mosquito pools 1136Sentinel chickens 805

5

1

180

72251

57

3

1

5

2

41

1

2

1

1

2

1 1

32

1

0

5

10

15

20

25

30

35

40

45

50

55

60

Num

ber of Cases

2/21/20042/28/20043/6/20043/13/20043/20/20043/27/20044/3/20044/10/20044/17/20044/24/20045/1/20045/8/20045/15/20045/22/20045/29/20046/5/20046/12/20046/19/20046/26/20047/3/20047/10/20047/17/20047/24/20047/31/20048/7/20048/14/20048/21/20048/28/20049/4/20049/11/20049/18/20049/25/200410/2/200410/9/200410/16/200410/23/200410/30/200411/6/200411/13/2004

Week of Onset**

Human West Nile Virus CasesCalifornia, 2004

WNNDWNFUNK

+ bird (2/24/04)

+ mosquito(04/14/04)

+ human(5/14/04)

+ chicken(5/17/04)

+ horse(06/20/04)

As of December 7, 2004 Total number of human West Nile cases: 766* West Nile Neuroinvasive Disease: 221 West Nile Fever: 277 Unknown: 268

Source: Viral & Rickettsial Disease Laboratory California Department of Health Services

FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV

• Onset dates not available for all patients• Birds, mosquitoes: date of collection; testing conducted at UC Davis, bird necropsy at CAHFS• Chickens: date of probable seroconversion; testing conducted at DHS• Equines: testing conducted at CAHFS; CDFA lead agency

Week of Onset

2/244/14

5/14

5/17

6/12

Sequence of WNV detection events in California relative to human case onset, 2004

Dead Bird SurveillanceDead Bird

Surveillance

Dead Bird Surveillance Program 2000 - 2004

Year Reported Tested Positive

2000 40 20 0

2001 68 18 0

2002 3,666 653 0

2003 8,650 1,765 96

2004 93,057 5,728 3,232

Number of WNV Positive Dead Birds 2004 (n=3,232)

1-30

31-61

62-100

101-200

Over 200

Prevalence of WNV in Tested Dead Birds*, 2004

10 – 19 %

20 – 39 %

40 – 59 %

60 – 79 %

80 – 100 %

* Prevalence = (# pos birds/# tested birds) X 100

Importance of WNV Dead Bird Surveillance Program in 2004

• Early season WNV detectionEarliest indication of WNV activity in 53 / 58 California counties

• Only surveillance element that covered ALL 58 counties– Mosquito and sentinel chicken testing limited to

regions with vector control agencies• In 22 counties, dead birds were the only

evidence of WNV activity

American Crow

53%

Western Scrub Jay

19%

Yellow-billed Magpie: 9%

Other corvids (4 spp.): 3%

Non-corvids (85 spp.): 16%

92 species of WNV positive dead birds

Positive dead birds = 3,232Number tested = 5,728: 75% corvids (48% crow)

Non-corvid WNV positive species

House Finch 70House Sparrow 34Cooper’s Hawk 31Barn Owl 28Red-tailed Hawk 27American Robin 20Brewer’s Blackbird 19Lesser Goldfinch 18Sharp-shinned Hawk 17American Kestrel 16

Number positive

WNV in Squirrels• 65% (50/77) of tree squirrels

tested were WNV positive– Prevalence is comparable to

WNV in dead birds (57%).

• Four tree squirrel species tested positive – Fox, western gray, eastern

gray, and northern flying squirrel

• First report of WNV infection in northern flying and western gray squirrels

WNV Activity in Mosquitoes in 2004

House MosquitoHouse MosquitoCulex Culex pipienspipiens

CxCx. . quinquefasciatusquinquefasciatus

Encephalitis Mosquito Encephalitis Mosquito Culex tarsalisCulex tarsalis

Polluted water; residential and commercial sources

Agricultural, commercial, man-made or natural sources

Number of WNV Positive Mosquito Pools, 2004

Over 200 pools

100 - 200 pools

11 - 40 pools

1 - 10 pools

• Positive pools = 1,136 (14,602 tested)• 20 counties • 9 species ( 3 genera: Cx., Oc., An.)

WNV Positive Mosquito Species1136 pos. pools / 14,602 mosquitoes tested

CULEXquinquefasciatus 741 (65%)tarsalis 315 (28%)stigmatosoma 41 (4%)erythrothorax 19 (2%)pipiens 13 (1%)thriambus 3 (<1%)

Plus Oc. melanimon (2), Oc. squamiger (1) An. hermsi (1),

Minimum Infection Rates (per 1,000) by Species July - September 2004

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

An

herm

si

Cx

eryt

h rot

hora

x

Cx

pipi

ens

Cx

quin

que f

a sci

a tus

Cx

stig

ma t

osom

a

Cx

tars

alis

Cx

thr ia

mbu

s

Oc

mel

anim

o n

Oc

squa

mig

er

Min

imum

infe

ctio

n ra

te (p

er 1

,000

)

MIRs are calculated using the bias-corrected MLE methods in Pooled Infection Rate version 2.0 add-in for Microsoft Excel created by Dr. Brad Biggerstaff at CDC-DVBID.

120

2232

281919

3

85901 955 187

# pools tested

San Bernardino 8.5 Los Angeles 6.9 > 6.0Orange 6.1Kern 5.7 > 4.0Imperial 4.0Lake 2.8 Fresno 2.0 > 2.0Tulare 2.0Shasta 1.7Sacramento 1.6Sutter 1.2Riverside 1.6 > 0.1Butte 1.3Placer 1.0San Luis Obispo 0.3Merced 0.1San Joaquin 0.1Stanislaus 0.1No positive pools 0No mosquitoes collected

Minimum Infection Rate (MIR)*

Counties Submitting Mosquitoes

2004

* MIR = (# positive mosquito pools/total number of mosquitoes tested) X 1,000

Includes all species of mosquitoes

MIR in mosquitoes collected from four southern California vector control agencies*

0.02.04.06.08.0

10.012.014.0

April May June July Aug. Sept. Oct.

MIR

Cx. tarsalis Cx. quinquefasciatus*San Gabriel MVCDGreater LA VCDNorthwest MVCDSan Bernardino VCP

2004

WNV Activity in Sentinel Chickens in 2004

Negative flockPositive flock

55 agencies231 flocks

Sentinel Chicken Surveillance Program 2004

• 805 seroconversions

• 22 counties with seroconversions

• 143 / 231 flocks seroconverted

• 805 seroconversions

• 22 counties with seroconversions

• 143 / 231 flocks seroconverted

WNV Seroconversions in 2004WNV Seroconversions in 2004

Human WNV Infections, 2004*

• 828 human infections from 23 counties–66 from blood banks 15 (22.7%)

developed symptoms• 777 symptomatic cases

–684 with known clinical presentation–395 (58%) West Nile fever (WNF)–289 (42%) West Nile neuroinvasive

disease (WNND)–93 unknown clinical presentation

• 27 fatalities*As of 1/27/05

California Human Case Statistics

• 777 symptomatic cases:– Median age all cases = 52 yrs (range: 2-94)– Median age WNND = 58 yrs (range: 4 – 94) – Median age WNF = 50 yrs (range: 2 –91)– 62% male

• 27 WNV-associated fatalities:– Median age = 76 yrs (range: 26-94)

• Known mosquito bite: 26.5%

Human WNV Incidence, by Age Group and Clinical CategoryCalifornia, 2004

0

0.5

1

1.5

2

2.5

3

3.5

0-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80+

Age Group

Inci

denc

e pe

r 100

,000

WNF

WNND

Week of Onset for Human WNV Cases California 2004 (n=643)

Week of Onset for Human WNV Cases California 2004 (n=643)

* Onset dates not available for 135 patientsSource: Viral & Rickettsial Disease Laboratory

California Department of Health Services

05

101520253035404550556065707580859095

100

Num

ber of Cases

5/1/2004

5/8/2004

5/15/2004

5/22/2004

5/29/2004

6/5/2004

6/12/2004

6/19/2004

6/26/2004

7/3/2004

7/10/2004

7/17/2004

7/24/2004

7/31/2004

8/7/2004

8/14/2004

8/21/2004

8/28/2004

9/4/2004

9/11/2004

9/18/2004

9/25/2004

10/2/2004

10/9/2004

10/16/2004

10/23/2004

10/30/2004

11/6/2004

11/13/2004

Week of Onset

WNNDWNFUNK

7/31- 8/13

5/14 10/30

Reported WNV Human Cases by County, 2004

828 infections

WNV activity (number of reported human cases)

WNV activity (no human cases)

15

1

197

116329

60

7

1

6

3

64

2

2

1

1

10

1 1

33

1

3

1

CA Total: 2.4

Tehama 17.8 >15

San Bernardino 11.5Glenn 11.3 >10

Kern 9.0Riverside 7.2 >5

Shasta 3.7Butte 3.4Los Angeles 3.4Lassen 2.9 >1Orange 2.2Fresno 1.8Lake 1.7

Others >0

Reported WNV cases per

100,000 people

2004

Incidence in:Arizona = 7.6Nevada = 2.2Oregon = 0.1Colorado = 6.4

CO 2003 = 68.5

2004 Equine WNV Data2004 Equine WNV Data

•• 540 WNV infected horses (32 counties)540 WNV infected horses (32 counties)

•• 230 (42%) died / euthanized230 (42%) died / euthanized

•• Vaccination statusVaccination status-- 22 properly vaccinated22 properly vaccinated-- 145 improperly vaccinated 145 improperly vaccinated -- 356 unvaccinated356 unvaccinated-- 17 unknown17 unknown

•• First positive finding of WNV in 2 countiesFirst positive finding of WNV in 2 counties

Week of Onset for Equine WNV CasesWeek of Onset for Equine WNV CasesCalifornia, 2004 California, 2004

0

10

20

30

40

50

60

5-Ju

n12

-Jun

19-J

un26

-Jun

3-Ju

l10

-Jul

17-J

ul24

-Jul

31-J

ul7-

Aug

14-A

ug21

-Aug

28-A

ug4-

Sep

11-S

ep18

-Sep

25-S

ep2-

Oct

9-O

ct16

-Oct

23-O

ct30

-Oct

6-N

ov13

-Nov

Date of onset (week ending)

Num

ber o

f cas

es

June 12 Nov 3

Aug 15 – Sept 4

Equine Cases