WNV Confirmation in US Blood Donors 20032005 and Data in Support of WNV IDNAT Triggers

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WNV Confirmation in US Blood Donors 2003-2005and
Data in Support of WNV ID-NAT Triggers

• Susan L. Stramer, Ph.D.
• Blood Products Advisory Committee Meeting
• April 27, 2007

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Confirmation of Infection among Donors Identified
by Minipool and Individual Donation Nucleic Acid
Amplification Testing (NAT) for West Nile virus
(WNV) RNA in the United States from 2003-2005

• S.L. Stramer, J.P. Brodsky
• S. G. Caglioti
• D.M. Strong
• representing all Roche Centers

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Background

• Donor screening for WNV RNA by NAT began in June
  2003 prior to the onset of the national epidemic
  for that year
• During 2003-2005, all blood programs in the US
  performed investigational NAT for WNV in
  minipools (MP) or individually (ID) during
  epidemic periods and in epidemic locations
• Conversion from MP to ID NAT was dependent on
  site specific triggers e.g., 2 positive cases
  and a frequency of 11000 positive donations

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Methods

• Three blood collection/testing programs
  contributed data representing greater than 80 of
  blood collected in the US, or over 4 million
  donations per WNV season, and covering all
  geographic regions
• Testing for WNV occurs throughout the year in all
  US areas however, to focus on incidence of new
  cases reported each year, this report covers only
  the epidemic periods for a given year, defined as
  the dates of collection between the first and
  last WNV confirmed-positive blood donor

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WNV Screening Tests

• All donations from 2003-2005 (and ongoing) were
  tested for WNV RNA by the
• Gen-Probe/Chiron WNV Assay (Transcription
  Mediated Amplification TMA) in MPs of 16 using
  either eSAS (semi-automated system) or the
  TIGRIS (automated system)
• Sites included
• American Red Cross (testing performed at 5 ARC
  National Testing Laboratories)
• United Blood Services (testing performed at 2
  Blood Systems Laboratories)
• All contract collection facilities sending
  testing to the above
• Represents all areas within the US

Gen-Probes WNV Assay on the eSAS platform was
FDA licensed on 12/1/05 (and on the automated
TIGRIS platform on 2/20/07)
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WNV Screening Tests

• Roche WNV PCR in MPs of 6 using the TaqScreen WNV
  Test on the Cobas Ampliprep and Taqman platforms
• Sites included (12)
• Puget Sound Blood Center (WA)
• Stanford Blood Center (CA)
• Gulf Coast Regional Blood Center (TX)
• Community Blood Center of Greater Kansas City
  (MO)
• Mississippi Valley Regional Blood Center (IA)
• Life Source (Institute of Transfusion Medicine)
  (IL/PA)
• Siouxland Community Blood Bank (IA)
• Minneapolis Memorial Blood Center (MN)
• New York Blood Center (NY)
• Floridas Blood Centers (FL)
• Central Pennsylvania Alliance Laboratory (PA)
• South Bend Medical Foundation (IN)
• All contract collection facilities sending
  testing to the above

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WNV Confirmation

• TMA and PCR initially reactive samples considered
  confirmed () if they met one of the following
  criteria
• Initial test repeated as reactive in the original
  or modified test formatALT NAT (preferably from
  an independent sample from the index donation)
• Index donation sample tested WNV IgM/IgG positive
  (progam dependent)
• Abbott Laboratories
• Focus Diagnostics
• State Public Health Laboratories
• Donor follow up samples tested reactive by
• TMA and/or PCR
• IgM/IgG
• Quantitative PCR
• National Genetics Institute

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WNV RNA Detection in US Blood Donors
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Number of WNV RNA Positive Donors Reported by
Week, 2003-2005
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WNV Confirmed Positives Sorted by Detection
Method (MP or ID NAT Only) coupled with
Presence/Absence of Antibody
67224291 (22) required ID NAT for detection
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Viral Loads WNV Confirmed Positive Donations
1013/1329 (76) total samples submitted for quant
PCR 750 (74) were Ab neg
N 202 48 10
3 0 263
N 46 195 206
248 55 750
Copies/mL
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Gen-Probe TMA S/CO Values of Confirmed Positive
(CP) and False Positive (FP) WNV Reactive Blood
Donors at Index
1005 of 1137 (88) confirmed pos have S/CO gt 17
Number
gt
S/CO
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Total False Positives Reported During Relevant
Date Ranges
540 donors of 722 had follow up samples testing
both RNA and Ab nonreactive
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Results of WNV Confirmatory TestingN1329
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Same vs Alternate NAT Reactivity at Index1196 of
1309 Total Tested by Both Methods1094 (91.5)
Reactive by at Least One Method
Primary and Alternate NAT have equivalent
sensitivity
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Conclusions - PPV

• The PPV of the screening algorithm (65)
  indicates the need for confirmatory testing
• 69 of false positives driving the lower PPV
  obtained during periods of ID NAT
• The PPV of index donation confirmatory algorithm
  is 100 using follow-up testing results as the
  gold standard
• All donors who are confirmed positive based on
  index donation results have been accurately
  classified as WNV infected (i.e., no false
  positives observed)

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Conclusions - Sensitivity

• Sensitivity of the confirmatory algorithm based
  on index sample testing approximates that based
  on follow-up sampling, indicating very little
  additional value is obtained by follow-up testing
  
• 99.0 based on repeat NAT () and Ab () at index
  (including those Ab () at index and confd by
  f/u)
• 90.3 by repeat NAT ()
• 23.5 by index Ab ()
• A confirmatory algorithm requiring follow-up
  testing will never have 100 sensitivity in
  practice because not all donors will participate
  in follow up

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Conclusions - NPV

• The few true positive donors who would not be
  classified as confirmed positive based on index
  testing would already have been counseled for
  possible WNV infection, been deferred for 120
  days, and components from their donations would
  have been quarantined thus there is no adverse
  impact on blood safety by eliminating follow-up
  testing

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Triggering

• Need to trigger (convert from MPgtID NAT) during
  epidemic periods
• based on low viral loads of WNV compared to HIV
  or HCV
• 22 of WNV NAT () samples detected required ID
  NAT
• 26 of detected samples were Ab positive of which
  majority (81) required ID NAT
• Most systems have implemented some type of
  trigger
• not standardized
• no method exists for site to site communication
• Triggering has been successful however, 2 WNV
  breakthrough cases occurred in 2006 (MMWR 2007)

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Triggering

• Based on need for improvement, AABB WNV Task
  Force representing blood industry developed Assn
  Bulletin 07-02 (4/3/07)
• Received input from CDC and FDA
• Recommendations involve use of a minimum trigger
  that has been shown to be feasible and has
  relatively high effectiveness (81 Custer et
  al., 2004)
• First validation was 2002 retrospective study
  based on frequency of WNV clinical disease
  (11000) and observation of 1 MP-neg unit/4
  MP-pos units (Stramer et al., NEJM, 2005)

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AABB AB 07-02

• Minimum criteria based on initial reactive
  donations and rapid time to respond (within 24 h)
  due to the short duration of the ID-NAT-only
  window period (2-7 days)
• Reversion back to MP NAT following 7 days without
  a repeatable or Ab () ID NAT reactive
• Communication plan based on the existing testing
  sites that have entered data into the AABB web
  site and therefore have had communication plans
  in place for their institutions and their
  customers
• Missing link then is communication between
  facilities contact information and states for
  which collected donations are tested are provided
  as an attachment to the AB

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AABB AB 07-02

• Sites for which collections occur in
  adjacent/overlapping areas should be
  communicating!
• Tools for tracking activity
• Site specific maps, etc.
• AABB WNV NAT-reactive donor website for which new
  cases should be added as quickly as feasible
• Donors entered by residential zip code
• Maps provided by CDC/USGS for human WNV activity
• CDC reports of avian/mosquito activity
• These tools can be used as part of planning
  activities within facilities and between
  facilities can be sent by email on a weekly
  basis to trigger communication

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Minimum Criteria

• Feasible, or it wont be done!
• Real time
• 2 WNV NAT reactives
• Rate of gt11000
• If fewer than 1000 collections/week, use weekly
  collections should combine with
  adjacent/overlapping facilities
• May have long intervals between 1st and 2nd
  reactive that may lead to false negative MP NAT
  results
• Defined geographic area to which the above two
  criteria are applied
• Most feasible/standardized method is based on
  number of collections
• lt1000/week cannot segment your facility
• lt5000/week gt interval between 1st-2nd is 7 days
  (rolling period)
• gt5000/week gt interval between 1st-2nd is 3 days
• Monitor number of donations between 1st-2nd
  trigger if lt2000 collections during interval

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2006 West Nile Virus Activity in the United
States(Reported to CDC as of January 3, 2007) N
4,180
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2006 West Nile Virus Human Neuroinvasive
Disease Incidence in the United States (Reported
to CDC as of January 3, 2007)
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2006 West Nile Virus Viremic Blood Donor Activity
in the United States(Reported to CDC as of
January 3, 2007) N 340
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West Nile Virus Biovigilance Network U.S./Canada
Map Suspected Cases by Postal Code
439 CP 64 FP 4 cannot conclude
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Logistics

• WNV ID NAT is a balance between sensitivity and
  capacity
• Largest labs may have capacity for 1000
  samples/day or 1200 samples/automated
  instrument/day
• Reagent performance issues or other sources of
  false positivity may cause sites to artificially
  trigger early or extend the time of ID NAT
• Repeat NAT can be used to eliminate probable
  low-level false positives

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2006 WNV ID NAT Calendar(as reported by regions)
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2006 WNV ID NAT Total Donations Tested(as
reported by regions)
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Course of Infection in Platelet Recipient Leiby
et al, NEJM, 1999 341(16)1237-1239
Signal/Cutoff (s/c)
PCR HC positive
Days Posttransfusion