Performance of the tandem ICON strep A® enzyme immunoassay system for detection of group a streptococci from oropharyngeal swabs

Abstract

AbstractThe Tandem ICON Strep A® (TISA Hybri‐tech, Inc.) was compared to culture for detection of group A streptococci, using throat swabs obtained from patients with symptoms of pharyngitis. Each swab was first inoculated to a 5% sheep blood agar plate and then tested for streptococcal antigen using the TISA. Cultures were incubated anaerobically at 35°C for 36 to 48 hours unless positive following overnight incubation. Group A streptococci were recovered in culture and serologically identified from 163 (21.0%) of the 776 swabs processed. The sensitivity and specificity of the TISA were 76.7% and 96.4%, respectively, whereas the predictive values of positive (PVP) and negative (PVN) results were 85.0% and 94.0%, respectively. However, TISA specificity ranged from 93.6% in one of 3 lots tested to 99.1% in another (P < 0.005). The PVP of the former lot was 76.3%, whereas that of the latter was 95.6% (P < 0.005). The relative lack of sensitivity and lot‐to‐lot variation observed with the TISA in this study indicate that the product is not a suitable alternative to a competently performed throat culture.