Optical immunoassay for rapid detection of group A beta-hemolytic streptococci. Should culture be replaced?

T. A. Schlager, G. A. Hayden, W. A. Woods, S. M. Dudley and J. O. Hendley
Department of Pediatrics, University of Virginia Medical Center, Charlottesville, USA.

OBJECTIVE: To evaluate an optical immunoassay rapid antigen test to detect group A beta-hemolytic streptococci directly from throat swab specimens. DESIGN: Criterion standard with "blinded" comparison. Double-swab pharyngeal samples were obtained; one swab was cultured and the other was used for the rapid antigen test. SETTING: Microbiology laboratory in a primary care center at a university teaching hospital. PATIENTS: Two hundred sixty-two outpatients with pharyngitis. MAIN OUTCOME MEASURE: The results of the optical immunoassay rapid antigen test were compared with results of standard aerobic culture. RESULTS: Sixty-two (24%) of 262 samples were culture-positive; 48 of these 62 were positive by the optical immunoassay rapid test (sensitivity, 77%). Of the 200 culture-negative samples, seven (4%) were positive by the rapid test (specificity, 96%). CONCLUSION: The optical immunoassay performed well, but like other rapid tests, is not sensitive enough to replace standard culture for detection of group A beta-hemolytic streptococci.

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