Rapid Influenza Diagnostic Testing (RIDT) April 2014

A Word about…
Rapid Influenza Diagnostic Testing
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 85-100%).
• 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
– 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 (RTPCR 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 RTPCR 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
• 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.
• 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

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