Evaluation of the Rapid Detection Test for Influenza A and B Viruses Using Neuraminidase Activity

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Abstract
The ZstatFlu® test (ZymeTx, USA) is a rapid detection kit for influenza A and B viruses. Thistest is based upon the reaction between viral neuraminidase from influenza viruses and a chromogenicsubstrate. The clinical performance of the ZstatFlu® test was determined by comparisonwith viral isolation in cell culture. A total of 176 respiratory specimens from 172 pediatric patientswith influenza like illnesses during the 1998/99 season were tested. Influenza viruses were recoveredfrom 97 specimens (type A: 6, type B: 91) in cell culture. ZstatFlu® demonstrated 67.4% sensitivity (29/43) and 62.7% specificity (37/59) for throat swabs. Of the 22 ZstatFlu®-positive, culture-negativethroat swabs tested by RT-PCR, 18 were positive by RT-PCR. ZstatFlu® showed 48.1% sensitivity (26/54) and 90.0% specificity (18/20) for nasopharyngeal aspirates. Of the two ZstatFlu®-positive, culture-negative nasopharyngeal aspirates tested by HI titer of paired sera, one showed a 4-fold increaseof HI titer. Nasopharyngeal aspirates therefore showed lower sensitivity than throat swabs atthis test, different from EIA test kits such as Directigen FluA® or FLU OIA®. Overall, only 5 specimenswere false positive by the ZstatFlu® test. Therefore, this test demonstrated high specificity andpositive predictive value. In conclusion, the ZstatFlu® test is useful for the rapid detection of influenza A and B viruses to identify patients who need antiviral treatment.

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