Variations in positive predictive values for rapid influenza tests for 2009 pandemic influenza a (pH1N1)--Arizona,...

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.

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.

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.

Arizona.

Seven Arizona laboratories submitted positive RIDT clinical samples to Arizona State Public Health Laboratory (ASPHL) for confirmatory rRT-PCR testing.

The PPV was calculated on the basis of rRT-PCR-positive results for April through October.

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).

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.