Superiority of conventional culture technique over rapid detection of group A Streptococcus by optical immunoassay.

An optical immunoassay (OIA) has been reported to be more sensitive than conventional culture for the detection of Group A Streptococcus, eliminating the need for culture. We attempted to confirm the sensitivity and specificity through a laboratory quantitation study and a clinical trial. OIA did not detect Group A Streptococcus below 10(5) colony forming units (CFU). Culture detected Streptococcus to 10(2) CFU from the inoculated swab. In the clinical study, throat swabs were obtained from 77 patients in an outpatient clinic. Compared with culture, the sensitivity of OIA was 78% and the specificity was 90%. These results demonstrate that OIA was less sensitive than culture in seeded experiments and missed 22% of positives in clinical practice. Our study, contrary to previous reports, suggests that OIA is not sensitive enough to be used as the sole assay for Group A Streptococcus pharyngitis.