Real-time PCR vs standard culture detection of group A beta-hemolytic streptococci at various anatomic sites in tonsillectomy patients.

Objective: To compare rates of group A beta-hemolytic streptococci (GABHS) detection by real-time polymerase chain reaction (rtPCR) and standard culture (SCx) at different anatomic sites to determine whether a more patient-friendly site (eg, retromolar trigone or gingivobuccal sulcus) would yield results similar to the tonsillar surface. Real-time polymerase chain reaction can detect GABHS at rates equal to SCx, and results require only a few hours.

Design: Prospective study.

Setting: Tertiary care setting.

Patients: The study population comprised 130 patients undergoing tonsillectomy or adenotonsillectomy.

Intervention: At tonsillectomy, swabs were taken of pharyngeal tonsil surface, pharyngeal tonsillar core, inferior gingivobuccal sulcus, and retromolar trigone. Tissue samples were taken from tonsil core and adenoid. All comparisons between methods and sites were made using the McNemar test for comparing correlated proportions. All calculated P values were 2-sided.

Main Outcome Measure: Detection of GABHS by rtPCR and SCx.

Results: In 41 cases (32%), GABHS was detected at 1 or more sampled sites, and 29 of those positive were detected on the tonsil surface-SCx and rtPCR results were both positive in 28 (97%). Of these 29 cases, results from the gingivobuccal site were positive by both rtPCR and SCx in 4 (14%), rtPCR only in 3 (10%), and SCx only in 3 (10%). Of the 7 tonsil surface-positive cases with retromolar trigone swabs, results were positive by rtPCR only in 1 (14%) and SCx only in 2 (29%).

Conclusion: Whether rtPCR or SCx is used, swabs of gingivobuccal sulcus and retromolar trigone do not accurately reflect GABHS populations on the tonsil surface.