Abstract
Context: Rapid influenza diagnostic tests (RIDTs) are used for influenza screening, clinical decision making, and influenza surveillance. In August 2009, a hospital reported increased false-positive RIDT results to the Arizona Department of Health Services. Because of reported RIDT low sensitivities (40%-62%) for 2009 pandemic influenza A (pH1N1), the hospital's report raised further concerns about the specificity and clinical utility of RIDTs.
Objective: To determine the positive predictive value (PPV) of RIDTs compared with real-time reverse transcription-polymerase chain reaction assay (rRT-PCR) using Centers for Disease Control and Prevention (CDC) protocols and primers as a standard.
Design: A standardized survey collected information including RIDT brand/lot number, training of personnel performing test, type of laboratory, swab and specimen type, time from collection to testing, sample storage, and viral transport medium.
Setting: Arizona.
Participants: Seven Arizona laboratories submitted positive RIDT clinical samples to Arizona State Public Health Laboratory (ASPHL) for confirmatory rRT-PCR testing.
Main Outcome Measure: The PPV was calculated on the basis of rRT-PCR-positive results for April through October.
Results: Results from 600 specimens using 1 of 4 RIDTs were available. Median pH1N1 PPV was 80% (range: 62%-91%) when calculated by RIDT brand. A significant difference in PPV was identified between the 2 largest facilities, which used the same RIDT brand, BinaxNOW Influenza A&B, (Laboratories A, 33% and B, 92%, [P < .01]). The facilities reported similar testing practices except lot numbers used and timing of testing. Laboratory A used lot 003684 and performed testing within 1 hour of collection; Laboratory B used multiple lots, excluding lot 003684, and performed testing within 24 hours. Laboratory A switched RIDT brands and noted a significant PPV increase from 33% to 91% (P < .01).
Conclusions: Wide PPV variability combined with documented low sensitivity among RIDTs for pH1N1 diagnosis increases concerns about their specificity and clinical and epidemiologic utility for influenza.