Automated Detection of Streptococcus pyogenes pharyngitis using Colorex Strep A CHROMagar and WASPLab™ Artificial Intelligence Chromogenic Detection Module Software.

Colorex Strep A Agar (CHROMagar, Paris, France) was evaluated with the PhenoMATRIX™ Chromogenic Detection Module (CDM) (Copan Diagnostics Inc., Murrieta, CA) software to detect Group A (GAS) from throat specimens. The software results were compared to manual plate image reading. In addition, GAS PCR was performed on all specimens. A true positive was defined as culture positive (by either PhenoMATRIX™ CDM or manual) confirmed as GAS by MALDI-TOF MS plus any culture negative specimens that were positive by both initial and repeat PCR. Of 480 specimens, 96 were considered true positives. Software reading of the chromogenic agar for suspect colonies detected 110 orange colonies compared to technologist reading which interpreted only 93/110 (84.5%) as positive. None of the 361 cultures interpreted as negative by the PhenoMATRIX™ CDM software were positive by manual reading. When compared to true positive results, the percent sensitivity and specificity were 96.9% and 100% for PCR, 87.5% and 97.7% for technologist reading of chromogenic agar, 90.6% and 94.0% for software reading of chromogenic agar, 83.3% and 97.7% for technologist reading for beta-hemolysis on blood agar, and 39.5% and 83.1% for technologist reading for beta-hemolysis on blood agar, respectively. The software had the most accurate results of the non-molecular based testing, detecting all suspect colonies from the chromogenic agar, and identifying 3 additional true positives that were missed by manual reading. The PhenoMATRIX™ CDM software and the Colorex Strep A Agar can improve detection of GAS from throat specimens and compared favorably to molecular testing.