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Influenza Testing: Update & Recommendations for Point-of-Care Testing. Gary Overturf, M.D. Professor, Pediatric Infectious Diseases & Pathology Medical Director, Infectious Diseases TriCore Reference Laboratories. Diagnostic Tests for Influenza.

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influenza testing update recommendations for point of care testing

Influenza Testing: Update & Recommendations for Point-of-Care Testing

Gary Overturf, M.D.

Professor, Pediatric Infectious Diseases & Pathology

Medical Director, Infectious Diseases

TriCore Reference Laboratories

diagnostic tests for influenza
Diagnostic Tests for Influenza
  • Serology: Acute & convalescent specimens and/or IgG and IgM; 14 – 28 days; retrospective diagnosis.
  • Primary Culture: NP, throat or nasal wash; cell culture in MKC (VERO and MRC-5) & embryonated hens eggs: 5 to 10 days.
  • “Accelerated Culture”(e.g. Shell vial); 48-72 hrs
  • Flourescent Antibody (FA; DFA) :TAT 24 hours.
  • Rapid testingin the Virology Laboratory:

- Flourescent antibody staining (e.g. DFA): 1 to 4 days

- RT-PCR: TAT 2-4 hours after arrival in laboratory; practical time for conventional resporting: 24 hours

examples of point of care tests for influenza a and b infections
Examples of Point-of-Care Tests for:Influenza A and B Infections
  • Point-of-Care Tests: < 15 minutes

Directigen EZ Flu A (BD) A+B

QuickVue (Quidel) A&B

Flu OIA (Thermo BioStar) A&B

ZstatFlu (Zyme Tx) A&B

BinaxNOW (Inverness) A&B

TRU FLU (Meridian) A&B

XPECT Flu (Remel) A&B

  • Some approved for nasal wash; some NP swab; others both
  • Range in cost of test = ~ $10 - $35, direct cost.
reliability of poc testing for influenza
Reliability of POC Testing for Influenza
  • CDC Evaluation: detection of novel-H1N1 (MMWR August 6, 2009).
  • Sensitivities: Quickvue 69%; Directigen EZ 49%; BinaxNOW 40% (overall range = 49 – 69%)
  • Previous Studies; range = 10 – 51%
  • Positive tests are reliable; negative tests, not reliable.
  • Due to limited sensitivities of POC tests, interpretation of the test results should be done with care.
utility of influenza testing
Utility of Influenza Testing
  • During seasonal influenza, 5% -~ 10% of patients visiting physicians offices may have influenza but 20% – 50% may have respiratory symptoms.
  • Therefore, a minimum of ~ 5 - 20 patients would need to be tested for every true positive assuming a ~ 50% sensitivity; adds $10 - $20 cost/patient tested. When the need to know is high; duplicate FA testing adds $25– $35/patient.
  • Only patients testing positive are candidates for antivirals if within 48 – 72 hrs of symptom onset. However, currently, only high risk patients, pregnant women and young children or seriously ill (e.g. hospitalized) are considered candidates for treatment.
recommendations for influenza viral testing
Recommendations for Influenza Viral Testing
  • Check current respiratory viral activity at TriCore web site ( Patients with ILI likely reflect infection with the prevalent community strain(s); most clinical decisions can be made with ILI plus a knowledge of the current viral epidemiology.
  • Screen with FA with valid laboratory testing (85 – 90% sensitivity); test only those patientswho are candidatesfor treatment/prophylaxis, or those to behospitalized. H1N1-novel RT-PCR should be ordered only for surveillance (DOH State is free with long TAT; TriCore will offer at charge).
  • POC Testing is not cost effective and does not benefitclinical decision making.
fda advice on rapid influenza testing
FDA Advice on Rapid Influenza Testing
  • When influenza activity is low, positives should be confirmed by DFA or RT-PCR; false positives are more likely
  • During influenza peak activity, falsenegatives are more likely; negative tests may not rule out influenza
  • None of the tests provide identification of other H-subtypes (H1, H2, H3, H5, H7, H9); FA does!
  • The tests have much lower sensitivity for adults than children because children shed more virus
additional fda advice re influenza testing
Additional FDA AdviceRE: Influenza Testing
  • Test sensitivities & specificities cannot be compared across package inserts
  • The performance of any rapid test using frozen samples may likely show greater sensitivity
  • Inadequate or inappropriate specimen collection, storage & transport are likely to yield false negative tests
  • Predictive values of individual tests will depend on the level of influenza activity, the types of virus circulating, age of patients and adequacy of collection
data synopsis from the fda throat nasal swabs or np wash
Data Synopsis from the FDAThroat/Nasal Swabs or NP Wash
  • Influenza A, Throat Swabs:

Pediatric Sens 65-90% Spec 81-91%

Adult Sens 24-91% Spec 69-94%

  • Influenza A, Nasopharyngeal Wash

Pediatric Sens 82-95% Spec 98-100%

Adult Sens 53-87% Spec 90-100%

  • Influenza A & B, Nasal Swab

Not Specified Sens 65-87% Spec 87-97%