A comparison between the Strep A Rapid Test Device and conventional culture for the diagnosis of streptococcal pharyngitis.
BACKGROUND
Rapid antigen detection tests are frequently used to diagnose pharyngitis due to Streptococcus pyogenes. Because a large number of kits are available commercially, performance characteristics may vary considerably. The present study evaluated one such kit currently in use in Canadian laboratories for which published evaluations are not available.


OBJECTIVE
To evaluate the performance characteristics of the Strep A Rapid Test Device (SARTD) (Nova Century Scientific Inc, Canada).


METHODS
Pharyngeal swabs from 818 patients with suspected streptococcal pharyngitis were tested. Swabs were initially inoculated onto the surface of a blood agar plate and then used to perform the rapid antigen test. The test was performed in accordance with the product monograph. Beta-hemolytic colonies were identified as S pyogenes using conventional means.


RESULTS
Four hundred ninety specimens were obtained from children and 328 from adults. S pyogenes was recovered from 171 (21%) patients. The SARTD detected S pyogenes antigens in 123 of 171 specimens from which S pyogenes was isolated on culture; the screen was negative in 610 of 647 specimens from which cultures were negative. The positive and negative predictive values of the SARTD were 76.9% and 92.7%, respectively.


CONCLUSIONS
The SARTD was much less sensitive (72%) than was suggested in the product monograph (90%). Laboratories should vigorously evaluate such products in-house, optimize specimen collection and transport, and choose more sensitive kits for use.
Forward
Kevin R
KR
Department of Pathology and Laboratory Medicine, Queen Elizabeth II Health Sciences Centre.
Haldane
David
D
Webster
Duncan
D
Mills
Carolyn
C
Brine
Cheryl
C
Aylward
Diane
D