West Nile Virus Surveillance and Epidemiology United States and Tropical Americas

1
West Nile Virus Surveillance and
EpidemiologyUnited States and Tropical Americas
2009 West Nile Virus Conference

• J. Erin Staples, MD, PhD
• Arboviral Diseases Branch
• Division of Vector-Borne Infectious Diseases
• Centers for Disease Control and Prevention
• Fort Collins, CO

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Overview

• Surveillance
• ArboNET
• Changes over time
• Epidemiology
• Incidence and location of WNV in U.S.
• Demographics
• Modes of transmission
• WNV in Tropical Americas
• Conclusions
• Future Direction
• Ongoing assessments
• Areas for further investigation

3
West Nile Virus Surveillance

• Formation of ArboNET

4
Response to West Nile Virus in 1999

• All lab testing done at CDC
• Ecologic data collected by state and city health
  depts
• Data kept in spreadsheets
• Identified a need to enhance arboviral disease
  surveillance on a national level

5
National Arboviral Surveillance System

• Electronic surveillance system developed by CDC
  in response to WNV introduction
• Unique system collecting both human and non-human
  data
• Dynamic system which can be adapted

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Objectives

• Monitor incidence as well as geographic and
  temporal spread of WNV and other arboviruses
• Disseminate information to public health
  officials, government officials, and the public
• Promotes prevention and control
• Stimulates research
• Evaluate the use of funds and need for additional
  resources

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Arboviral Surveillance

• Ecologic data
• Veterinary cases (e.g., horses)
• Dead birds
• Mosquitoes
• Sentinel (e.g., chicken, horses)
• Human data
• Disease cases (e.g. neuroinvasive, fever)
• Presumptive viremic donors (PVDs)

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Adaptation of ArboNET andArboviral Surveillance

• Start of ArboNET
• WNV human neuroinvasive disease (WNND) cases
• Non-human surveillance data

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Adaptation of ArboNET andArboviral Surveillance

• Revision of case definition

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Adaptation of ArboNET andArboviral Surveillance

• WNV fever cases
• WNV PVDs
• WNV transplant cases
• WNV pregnancy and breastfeeding cases
• Non-WNV arboviral disease cases

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Adaptation of ArboNET andArboviral Surveillance

• Revision of case definition
• AFP cases
• Hospitalization
• CV, VEE, YF

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Adaptation of ArboNET andArboviral Surveillance

• WNV clinical risk factors
• Laboratory testing
• CHK, CTF

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Adaptation of ArboNET andArboviral Surveillance

• NEDSS
• compliant

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Changes in WNV Laboratory testing

• WNV testing initially performed at CDC then
  transferred to state health depts
• Commercial assays licensed and used by increasing
  numbers of commercial and public health labs
• Less control over confirmation and QA/QC of WNV
  testing

See Poster 29 by Lehman and Poster 44 by Janusz
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Dissemination of Data

• Weekly updates posted online and EpiX
• Weekly updates of USGS maps with number of cases
  by state and county
• Regular MMWR updates
• Annual MMWR summary
• Peer-reviewed journal articles

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WNV Surveillance Totals, U.S., 1999-2008
Provisional Data as of February 13, 2009
17
Percent of all U.S. counties reporting non-human
WNV surveillance data to ArboNET by type and
year, 2002-2007
From Lindsey, Poster 27
18
Numbers of dead birds and mosquitoes tested among
counties reporting these data every year,
2002-2007
From Lindsey, Poster 27
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West Nile Virus Epidemiology

• United States

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First Reported WNV Activity by State, 1999-2008
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Number of states and counties reporting WNV
activity per year, U.S., 1999-2008
Number of Counties
Number of States
Year
22
Counties reporting WNV activity in humans and
non-human species, U.S., 2002-2007
From Lindsey, Poster 27
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Non-human Epidemiology

• United States

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Most Common WNV-Positive Mosquito Species, by
Positive Pools, U.S., 2001-2008

• Culex species
• Cx. quinquefasciatus
• Cx. pipiens
• Cx. tarsalis
• Cx. restuans
• Cx. salinarius

• Aedes species
• Ae. albopictus
• Ae. vexans

• 64 mosquitoes species have tested positive for
  WNV in the U.S. from 1999-2008

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Equine WNV Disease Cases Reported,U.S., 1999-2008
Total 24,859 cases
Vaccination introduced
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Human Epidemiology

• United States

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Reported WNV Human Disease Cases U.S., 1999-2008

• 28,943 cases from 1,824 counties in 47 states and
  DC
• WNND 11,807 (41)
• WNF 16,463 (57)
• Other clinical illness 673 (2)
• 1,130 (4) fatal cases

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Number WNV Human Disease Cases by Clinical
Syndrome, U.S., 1999-2008
9862
Number of Cases
4269
4156
3630
3000
2539
1338
62
66
21
Year
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Estimated Number of WNV Infections and Fever
Cases, U.S., 1999-2008

• Diagnoses and reporting of WNV fever varies by
  year and location
• WNND most reliable indicator of WNV disease
  activity in humans
• Based on serosurveys
• 140 WNV infections per 1 WNND case
• 28 WNV fever cases per 1 WNND case

140 x 11,807 WNND 1.65 million infections
28 x 11,807 WNND 331,000 WNV fever
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Incidence of WNND by Year, U.S., 1999-2008
Incidence per 100,000
Year
31
Average Annual Incidence of WNND,by County,
U.S., 2004-2007
32
Percent of WNND Cases by Month of Onset, U.S.,
1999-2007
Month
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Demographic and Clinical Information

• WNV Human Disease Cases
• United States

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Average Annual Incidence of WNND Cases by Sex and
Race, U.S., 1999-2007
35
Average Annual Incidence of WNND by Age Group,
U.S., 1999-2007
Incidence per 100,000
Age group (yrs)
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Cumulative Incidence of WNND cases by Age Group
and Sex, U.S., 1999-2007
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Incidence of WNND for Children and Adults, by
year, U.S., 1999-2007
Incidence per 100,000
Year
38
WNND Clinical Syndrome by Age Cohort,U.S.,
1999-2007
Data from 2004-2007 includes cases reported as
AFP only.
39
WNND Severity and Outcome by Age Cohort,U.S.,
1999-2007
Data from 2004-2007
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Transmission of WNV Without Mosquitoes
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WNV Transmission via Blood Transfusions

• 23 transfusion-associated WNV infections
  identified in 2002
• Beginning 2003, all blood donations screened
  using NAT on either pooled or individual samples
• PVDs reported to state health departments which
  report cases to ArboNET

Pealer et al. 2003. N Engl J Med. 3491236
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PVD Data from ArboNET
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WNV Transfusion-associated Disease

• 32 transfusion-associated WNV infections reported
  in literature
• Last documented cases in 2006
• CDC investigates multiple cases of possible WNV
  transfusion-associated disease annually
• Predominantly immunocompromised individuals
• Unable to substantiate due to lack of retention
  samples from the original blood unit

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WNV Transmission by Solid Organ Transplantation

• Cases of WNV infection from organ transplantation
  first recognized in 2002
• Seven cases of transplant-associated WNV
  infections documented in the literature
• 4 cases in 2002, 3 cases in 2005
• CDC investigates multiple cases of possible WNV
  transplant-associated disease annually
• Most recent case from LA in September 2008
• No current guidelines for routine screening of
  organ donors

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Other Modes of Transmission

• Documented in utero transmission of WNV
• One cases with definitive evidence and three with
  supportive evidence
• Breast-feeding associated WNV case

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Number of Neuroinvasive Disease Cases for by
Arboviral Disease, U.S., 1999-2007
3000
WNV
2500
2000
Number of WNV Cases
Number of Non-WNV Cases
1500
1000
500
0
Year
47
Non-human and Human Epidemiology

• Tropical Americas

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West Nile Virus in Tropical Americas
2001
2002
2003
2004
2004
2007
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Conclusions - 1

• ArboNET developed in response to WNV introduction
• Non-human activity has helped define the
  geographic location and spread of WNV
• WNV human disease may have reached endemic level
  in the U.S.
• WNND affects all age groups causing more deaths
  and encephalitis in individuals gt 50 years

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Conclusions - 2

• WNV has become the most common cause of arboviral
  neuroinvasive disease in the U.S.
• WNV activity has also been detected at a lower
  level in Tropical Americas

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Future Plans
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Ongoing Assessments

• Evaluation of ArboNET and arboviral surveillance
• Re-evaluation of WNV/Arbovirus case definitions
• Exploration of the ability of non-human WNV data
  to predict human WNV disease
• Determination of risk factors for severe WNV
  disease
• Capturing of extended clinical information
• Economic analysis of WNV vaccine

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Areas for Further Investigation

• Assess differences in WNV disease transmission
  between high and low risk areas
• Investigate difference in the spread and disease
  prevalence between U.S./Canada and Latin
  America/Europe
• Explore ability of PVDs to predict human WNND
• Develop guidelines for screening of organ donors
  for WNV
• Evaluate the development and use of WNV vaccine
  for humans

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Acknowledgments

• Jennifer Lehman
• Nicole Lindsey
• Marc Fischer
• Kristen Janusz
• Nick Komar
• Emily Zielinski-Gutierrez
• Robert Lanciotti
• John Roehrig

• Roger Nasci
• Lyle Petersen
• ADB EISOs/ArboNauts
• Ned Hayes
• Grant Campbell
• Terry Smith
• Dan OLeary
• Tony Marfin

• Peggy Collins and the ArboNET technical staff
• State/local health dept ArboNET surveillance
  coordinators