Experience with rapid latex agglutination testing for group A streptococcal pharyngitis in a pediatric group office...

We evaluated 2401 patients with suspected streptococcal pharyngitis with the Culturette 10-minute Group A Strep ID test during a 6-month period in order to determine its suitability for rapid diagnosis in a busy private office practice. Duplicate throat swabs were obtained for each child, and latex agglutination was performed within 15 minutes. In children with negative latex agglutination results, the second swab was cultured. All latex agglutination results were available within 20 minutes of collection, while the patients waited in the office. Seven hundred thirty-eight specimens were positive by latex agglutination. Seventy-eight of the 1663 latex negative specimens contained group A streptococci on culture (sensitivity 90 percent). Approximately 60 percent of these latex-negative, culture-positive specimens demonstrated 3(+)-4+ growth in culture, unlike previous studies ascribing false-negative latex results to low colony count specimens. Fifty percent of bacitracin-susceptible streptococci tested were not group A, indicating a relatively high occurrence of nongroup A beta-hemolytic streptococcal carriage in this patient population. The use of latex agglutination for detection of group A streptococcal pharyngitis was well-suited to our office practice, even during an extremely busy winter season. Although this assay appears to have a relatively high sensitivity, it is still prudent to culture latex-negative swabs to exclude group A streptococcal infection. The significance of nongroup A beta-hemolytic streptococci in our patient population was unclear. Further refinements are necessary.