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Home Eurosurveillance Edition  2013: Volume 18/ Issue 26 Article 4
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Eurosurveillance, Volume 18, Issue 26, 27 June 2013
Miscellaneous
Addendum for Euro Surveill. 2013;18(21)

Citation style for this article: Addendum for Euro Surveill. 2013;18(21) . Euro Surveill. 2013;18(26):pii=20514. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20514

For the article ‘A comparison of rapid point-of-care-tests for the detection of avian influenza A(H7N9) virus, 2013’ by C Baas et al. published on 23 May 2013, the authors wish to make the following addendum:

In our recent article, we described the sensitivity of six rapid point-of-care tests (POCTs) for the detection of avian influenza A(H7N9) and other avian and human influenza viruses [1]. Viruses of known infectivity titre were diluted and a limit of detection (LOD) of each kit for each virus was determined. Four of the kits tested were approved for the analysis of aspirate or wash specimens, while two, Clearview Exact Influenza A&B (Cat# IV506761) and Becton Dickinson BD Veritor System for rapid detection of Flu A+B (known as the ‘point-of-care (POC)’ kit (Cat# 256045), were approved only for the analysis of direct swab specimens.

As noted in our original article, these two POCTs that were approved only for use with direct swabs, were evaluated by dipping the swabs into the virus dilutions. This procedure may not have been appropriate for these tests and we concluded that these kits may perform better with actual patient swab specimens [1].

Since the publication of our article, we were advised by the manufacturer of the BD Veritor System, Becton Dickinson, the United States (US), that there was an additional version of the BD Veritor System for rapid detection of Flu A+B, known as the ‘laboratory kit’ (Cat# 256041), that has been approved in some countries for testing nasopharyngeal aspirates and washes and swabs in transport media [2]. Therefore our statement in [1] that “the BD Veritor tests are only approved for analysis of swab specimens” only applied to the kit we evaluated. To date the BD Veritor System Flu A+B laboratory kit has only been sold in the US, Canada, Hong Kong and the Republic of Korea, and was not available in Australia at the time of our initial evaluation.

The BD Veritor System POC kit which was used in our evaluation has been waived by the Clinical Laboratory Improvement Amendments (CLIA), indicating its appropriateness for use in a non-laboratory setting, whereas the laboratory kit is considered in the US to be moderately complex and as such has not been evaluated for CLIA-waived status [3]. While the laboratory kit is approved for analysis of aspirates, washes and nasopharyngeal swabs in transport media, it is not approved for the testing of direct swabs that are freshly collected from patients [2].

To determine whether the LOD of the new BD Veritor System laboratory kit for the avian influenza A(H7N9) virus A/Anhui/01/2013 was different from that of the BD Veritor System POC kit, we prepared new dilutions of the virus and tested these in duplicate using both kits. The laboratory kit was kindly provided free of charge by Becton Dickinson and was tested according to the recommended protocol. The LOD of the retested BD Veritor System POC kit was 1x105.5 TCID50/mL, the same result as that obtained in the initial evaluation [1]. The BD Veritor System laboratory kit had an improved LOD of 1x105 TCID50/mL. This LOD was the same as that obtained for the BD Directigen EZ and Quidel Sofia POCTs in the initial evaluation, making these three kits the most sensitive at detecting the A(H7N9) virus among those tested.

The improved performance of the BD Veritor System laboratory kit compared with the BD Veritor System POC kit is likely to be due to differences in the protocol for processing a liquid sample, for which the POC kit is not approved. The proportion of virus sample used following dilution was considerably higher for the laboratory kit (75%; 300 ml specimen + 100 mL diluent) compared with the POC kit (11%; 50 ml specimen + 400 mL diluent), for which the swabs were dipped into the liquid. However as described previously [1], the level of sensitivity achieved by all of the POCTs evaluated, including the BD Veritor laboratory kit, is poor compared to RT-PCR and are all likely to result in false negative results when analysing the majority of RT-PCR positive A(H7N9) clinical specimens.


References
  1. Baas C, Barr IG, Fouchier RA, Kelso A, Hurt AC. A comparison of rapid point-of-care tests for the detection of avian influenza A(H7N9) virus, 2013. Euro Surveill. 2013;18(21)=20487. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20487
  2. Becton Dickinson. BD Veritor System Overview. [Accessed: 19 Jun 2013]. Available from: http://www.bd.com/ds/veritorSystem/systemoverview.asp.
  3. Overturf GD. CLIA waived testing in infectious diseases. Pediatr Infect Dis J. 2008; 27(11):1009-12. 

 




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