Effect of using 2 throat swabs vs 1 throat swab on detection of group A streptococcus by a rapid antigen detection test.

OBJECTIVE To assess the effect of using 2 throat swabs vs 1 on rapid detection of group A streptococcus by the STREP A OIA MAX (hereafter, OIA MAX) test. METHODS Children aged 5 to 18 years with acute pharyngitis were randomized to 1 of 2 study groups. In group 1, one throat swab was obtained, streaked first on sheep blood agar, and then used for OIA MAX testing. In group 2, two throat swabs were obtained simultaneously. One swab was streaked first on sheep blood agar and then joined with the other swab for OIA MAX testing. In both groups, the pledgets in the collection-transport tube were incubated in Todd-Hewitt broth. A positive group A streptococcus culture either by sheep blood agar or Todd-Hewitt broth was confirmed by a latex agglutination test. RESULTS Three hundred sixty-three patients were enrolled, 177 in group 1 and 186 in group 2. Cultures were positive for group A streptococcus in 154 (42.4%) of 363 patients. The sensitivity and specificity of OIA MAX testing were 94.7% and 100.0%, respectively, in group 1, and 92.4% and 96.3%, respectively, in group 2. There was no statistical difference between the sensitivity, the specificity, and the predictive values of the OIA MAX test performed with 1 swab compared with those performed with 2 swabs (P>.10). There was no association between OIA MAX test sensitivity and the severity of pharyngitis as measured by the modified Centor criterion (history of fever, absence of cough, presence of pharyngeal or tonsillar exudates, and presence of cervical lymphadenopathy) scores. CONCLUSIONS The OIA MAX test yielded comparable sensitivity and specificity in both study groups. The use of 2 throat swabs instead of 1 swab did not increase the sensitivity of the OIA MAX test. The performance of the OIA MAX test did not depend on the severity of pharyngitis.