Evaluation of two rapid antigen assays, BioStar Strep A OIA and Pacific Biotech CARDS O.S., and culture for detection of group A streptococci in throat swabs

Abstract

Two rapid methods, BioStar Strep A OIA (OIA; BioStar, Inc., Boulder, Colo.), an optical immunoassay, and CARDS O.S. (O.S.; Pacific Biotech, Inc., San Diego, Calif.), a color immunochromographic assay, and two culture methods, one with 5% sheep blood agar (SBA) and one with Todd-Hewitt broth (TH; Remel, Lenexa, Kans.), were evaluated for use in the detection of Streptococcus pyogenes from pharnygeal swabs. Seven hundred forty-six double swabs (Culturette II) were processed, with OIA and SBA culture performed on one swab and O.S. and SBA culture performed on the other swab. The pledget from the Culturette II was incubated overnight in TH and was subcultured onto SBA for an additional 48 h in ambient air. All beta-hemolytic streptococci from culture were tested by a direct fluorescent-antibody test (Difco Laboratories, Detroit, Mich.). Specimens with discordant fluorescent-antibody test and rapid test results were also tested by using the Streptex latex agglutination reagent (Murex Diagnostics Limited, Dartford, England). The results obtained by all testing methods were compared with a combined test result ("gold standard"), which was defined as any positive culture detected by the SBA or TH culture methods and confirmed by Streptex latex agglutination or, in the case of negative results by both culture methods, a concomitant positive result by OIA and O.S. antigen testing. Sensitivity and specificity results for each of the methods were as follows, respectively: OIA, 81.0 and 97.5%; O.S., 74.4 and 99.0%; SBA culture, 92.3 and 98.3%; and TH culture, 86.4 and 100%. Both OIA and O.S. are suitable screening methods for detecting S. pyogenes directly from throat swabs but are of insufficient sensitivity to eliminate the need for backup cultures for specimens with negative OIA or O.S. results.

The utility of rapid antigen detection testing for the diagnosis of streptococcal pharyngitis in low-resource settings

“…Previous evaluations of the OIA MAX test in the USA have demonstrated a range of sensitivity from 79.3% to 94.7% and specificity from 96.3% to 100%. 15,[25][26][27][28][29] Our study demonstrated a range of sensitivity from 72.4% to 91.8% and specificity from 85.7% to 96.4%. The high negative predictive value in all countries suggests that a negative test would be useful to rule out GAS pharyngitis and potentially reduce unnecessary antibiotic treatment.…”

Adecuación del tratamiento de la faringoamigdalitis aguda a la evidencia científica

“…Por lo tanto, cuando se sospeche una infección faringoamigdalar por estreptococos del grupo A, el diagnóstico debe estar basado en un cultivo de frotis faríngeo o en una prueba rápida de detección de antígenos. Considerando la limitada sensibilidad de la prueba rápida [30][31][32][33] , en los casos en que ésta tenga un resultado negativo debería recurrirse al cultivo 30 .…”

Comparison of BioStar Strep A OIA optical immune assay, Abbott TestPack Plus Strep A, and culture with selective media for diagnosis of group A streptococcal pharyngitis

“…Although the rapid antigen tests had comparable sensitivities, neither was as sensitive as its corresponding selective-medium culture. In two recent reports, the BioStar OIA similarly had sensitivities of 84 and 81% (2,3). In addition, the BioStar OIA had an increased number of apparent false-positive results and a significantly decreased predic-tive value of a positive test (it is possible that some of these results were due to prior antimicrobial treatment).…”

“…In a study by Harbeck et al (4), the increased positivity rate of enhancedbroth culture and rapid antigen testing may have reflected a longer holding time between sampling and test performance, which has been shown to amplify antigen (1) and could also result in reduction of the viable inoculum. Subsequently, Dale et al (2) reported only 86% sensitivity for Todd-Hewitt broth culture. Under conditions of equal inoculum size, broth culture does not enhance the overall group A streptococcus recovery rate (6).…”

“…An early report of the optical immune assay (OIA) suggested that this new generation of test might have a sufficiently high sensitivity to obviate the need for a backup culture (4). Subsequent studies have not verified the anticipated sensitivity (2,3). Because of the difficulty of comparing independent studies, we undertook a direct comparison of the OIA for group A streptococcus detection with a secondgeneration enzyme immune assay and selective-medium culture in a blinded, comparative trial.…”