Clinical Performance of Foam vs Flocked Swabs

  collected from the anterior nares in a rapid antigen test for influenza A & B

Kathy Mack, Douglas Salamon, Erin Stoner, Jose Cuatas, Kimberley Scansen,  Bema Bonsu, Amy Leber, & Mario Marcon

Departments of Emergency Medicine, Nationwide Children’s Hospital, Columbus, Ohio, USA

Poster M8 at Pan American Society for Clinical Virology24th Clinical Virology Symposium

April 27 - 30, 2008 Daytona Beach, Florida, USA

Background: Posterior nasopharyngeal (NP) secretions collected by aspiration,

wash or swab are preferred for laboratory testing to diagnose respiratory viral

infections including influenza. However, anterior nares (AN) swabs are easier to

collect and better tolerated by patients, and some rapid influenza antigen tests

are FDA-cleared for this specimen type. There are limited data on the

performance of such tests with respect to the effects of swab composition.

Objective: This study compared the clinical sensitivity and specificity of a high

absorbency polyurethane foam swab versus a high surface area nylon flocked

swab collected from the AN for detecting influenza antigen.

Methods: For this prospective study, 100 children with symptoms suggesting

influenza were recruited with informed consent from a large academic pediatric

Emergency Department during the 2006-07 and 2007-08 influenza seasons. For

each subject, a high absorbency foam (Medical Wire Σ – Swab™ ) and high

surface area flocked nylon fiber (Copan USA) swab specimen was obtained from

left and right AN and placed in a transport tube (no transport medium). A

polyester swab specimen was also collected from the posterior NP on each

subject and placed in M4 transport medium. The AN specimens were tested for

influenza antigen in the main hospital laboratory using the Quidel QuickVue®

Influenza A+B Test. The posterior NP specimens in M4 were tested by culture,

DFA, and RT-PCR (Prodesse). The results of the latter tests were used to

establish the clinical performance of the Quidel test performed on the two AN

swab types.

Results: Influenza was diagnosed by culture and/or DFA in 49 subjects- 34

influenza A and 15 B. Influenza was diagnosed by RT-PCR in 56 subjects- 37

influenza A and 19 B.

 

Standard Method            Swab type     Antigen Sensitivity (%)       Antigen specificity (%)

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Culture &   DFA                 Foam                    78 (38/49)                              94 (48/51)

                                            Flocked                 61 (30/49)                              98 (50/51)

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RT-PCR                             Foam                     71 (40/56)                              98 (43/44)

                                            Flocked                 54 (30/56)                              98 (43/44)

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The intensity of the test band on most of the positive tests was  greater with the foam swab.

 

Conclusions: High absorbency polyurethane foam swabs are

preferable to high surface area nylon flocked fiber swabs for

detection of influenza virus in the Quidel QuickVue® Influenza

A+B Test.