A Word about… Rapid Influenza Diagnostic Testing (RIDT) Kelly L. Moore, MD, MPH Director, TN Immunization Program TDH Regional Epidemiology Meeting Montgomery Bell State Park April 30, 2014

RIDTs: Convenient but…how useful? Sensitivity (how likely is it to be positive if the patient has influenza) – 40-70%, but range of 10-80% has been reported vs. culture or RT-PCR Specificity (how likely it is to be positive for influenza and not other things) – 90-95% (range %). False negatives (missing it when it is there) more likely than false positives Recall “positive predictive value” PPV, “negative predictive value” NPV – Dependent on pre-test likelihood that the patient has the condition False-positive (and true-negative) more likely when virus not circulating widely – Beginning and end of the season and during summer False-negative (and true-positive) more likely when virus is circulating widely The Sentinel Provider Network is crucial – changes meaning of results

Minimize False Results Collect specimens as early in the illness as possible (ideally less than 4 days from illness onset). Follow manufacturer's instructions, including acceptable specimens, and handling. Follow-up negative results with confirmatory tests (RT- PCR or viral culture) if a laboratory-confirmed influenza diagnosis is desired. False negatives more likely if – Adult – Symptomatic 5 or more days – Upper respiratory specimen (e.g., nasal swab) When patient has lower respiratory tract disease

So you have RIDT results… When do you need real confirmation? Consider influenza testing by culture or RT- PCR to confirm results of an RIDT when: – RIDT negative + community influenza activity high + lab confirmation desired – RIDT positive + community influenza activity low + a false positive result is a consideration – Recent close exposure to pigs or poultry or other animals, novel influenza A infection possible

Testing Hospitalized Patients Influenza testing is recommended for hospitalized patients with suspected influenza. Empiric antiviral treatment should be initiated as soon as possible without the need to wait for influenza testing results Antiviral treatment should not be stopped based on negative RIDT results Implement infection control measures upon admission for any hospitalized patient with suspected influenza even if RIDT results negative Respiratory specimens can be tested for influenza by immunofluorescence, RT-PCR or viral culture. Serology is not for clinical management.

Conclusion Negative results of RIDTs do not exclude influenza virus infection Treatment should not be withheld from a patient hospitalized with signs and symptoms of influenza on the basis of RIDT results My view – Human psychology is can endanger patient lives in this situation – Instinct is for RIDT results to influence clinical judgment even when guidelines instruct one to ignore the RIDT Evidence suggests antivirals benefit hospitalized patients even if initiated after the first 2 days of illness Persons hospitalized with suspected influenza and not initiated on antiviral therapy are not given the best chance for recovery Treat the patient, not the test