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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