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Influenza Surveillance Viral Isolation Laboratory TX DSHS July 23, 2008

Martha Thompson, MPH Viral Isolation Team Leader Medical Virology Group Laboratory Services Section TX DSHS. Influenza Surveillance Viral Isolation Laboratory TX DSHS July 23, 2008. Viral Isolation . 2007-2008 Season Laboratory Diagnostics: Influenza Influenza testing: Viral Isolation Lab

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Influenza Surveillance Viral Isolation Laboratory TX DSHS July 23, 2008

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  1. Martha Thompson, MPHViral Isolation Team LeaderMedical Virology GroupLaboratory Services SectionTX DSHS Influenza Surveillance Viral Isolation Laboratory TX DSHSJuly 23, 2008

  2. Viral Isolation • 2007-2008 Season • Laboratory Diagnostics: Influenza • Influenza testing: Viral Isolation Lab • Cell Culture • Immunofluorescence • Hemagglutination/HA Inhibition • Levels of Identification • Specimen rejection criteria • Summary of isolates sent to CDC

  3. Influenza A specimens not subtyped (2) • B strains identified as B/Shanghai/361/2002-like (B/Yamagata) by the viral isolation laboratory

  4. Laboratory Diagnostic Testing: Influenza

  5. Rapid EIA Kits • Advantages • Rapid and on-site testing • Impact patient management • Simple • CLIA waved

  6. Limitations • Typing/Results • Flu + only • A or B • No subtyping • Variation between kits • Storage conditions • Acceptable specimens (includes type and time of collection) • Must follow manufacturer instructions • Less sensitive than viral culture or molecular • False negatives • PPV and prevalence in the community affect test performance

  7. These limitations affect test performance • Patient management • Use positive and negative predictive values to assess test performance • PPV: Probability of disease in a patient with a positive test result • PNV: Probability of no disease in a patient with a negative test result

  8. Test Performance Disease Test Result Sensitivity = TP/TP+FN Specificity = TN/TN+FP PPV= TP/TP+FP PVN = TN/TN+FN

  9. Positive predictive value: Prevalence=20% Disease Test Result Predictive Value Positive = TP/TP + FP = 380/380+64 = 85.6%

  10. Positive predictive value: Prevalence = 1% Disease Test Result Predictive Value Positive= TP/TP + FP = 19/19+80 = 19.1%

  11. Conclusion • When prevalence is low, the PPV is low and chance of getting a false positive increases • Confirm with culture during off season

  12. Other Methods • DFA • Quick TAT • No culture available for further studies • Serology • Positive results can be obtained even after viral shedding has stopped • Acute/convelescent serum required—delay in diagnosis • No culture available for further studies

  13. Advantages Rapid: Sensitive/Specific* High throughput can be obtained Identification of highly pathogenic strains of avian influenza possible Disadvantages Costly Risk of cross contamination Variability among protocols means variability among sensitivity/specificity rates No isolate available for further studies Real Time RT-PCR

  14. Cell Culture • Confirm virus is infectious • Antigenic characterization • Vaccine Studies • Antiviral resistance testing • Important for surveillance • Slower TAT • 2-10 days

  15. Immunofluorescence (IFA) • Indirect test • Antibody to Flu A and B antigens • Fluorescent tag • A, B, or Neg • If positive – continue with subtyping • Reagents in WHO kit

  16. Hemagglutination/HA Inhibition • Antisera to neutralize antigens • Blood as an indicator, agglutinates to antigen • Antigenic characterization

  17. Antisera Level of identification A(H3) A(H1) B/Shanghai/361/2002-like B/Malaysia/2506/2004-like Isolates to CDC Beginning, middle, and late season Patients who received vaccine Anything unusual Unable to subtype 2007-2008 WHO Influenza Reagent Kit

  18. WHO Summary: Weeks Ending Oct 6, 2008 – May 17, 2008

  19. Vaccine Strains • 2007-2008 Vaccine Strains • A/Solomon Islands/3/2006 (H1N1)-like • A/Wisconsin/67/2005 (H3N2)-like • B/Malaysia/2506/2004-like (B/Victoria) • A/Brisbane/10/2007 is a variant form of A/Wisconsin/67/2005 strain • All B strains identified by VI lab were B/Shanghai/361/2002-like (B/Yamagata)

  20. Specimen Rejection Criteria • Meet regulatory standards • Optimal specimen for testing • Expired transport media • Wooden sticks/Calcium alginate • Inhibitors to virus: preservatives • Cotton swabs • First AND Last name: on specimen AND submission form • 1 Specimen = 1 Submission form • DATE of COLLECTION

  21. Contact Information martha.thompson@dshs.state.tx.us Phone 512-458-7594 Fax 512-458-7293 Viral Isolation Laboratory 512-458-7111 x2452

  22. Useful Links Resource Manual for Seasonal and Pandemic Influenza http://www.dshs.state.tx.us/comprep/pandemic/flu%20outreach%20manual%2012-28-2007.pdf Laboratory Services Section http://www.dshs.state.tx.us/lab/

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