Efficacy of throat gargling for detection of group A beta-hemolytic streptococcus

Abstract

The purpose of our study was to investigate the suitability of throat gargling with sterile saline as an alternative method to throat swabs for detection of group A beta-hemolytic streptococcus (GAS). Throat specimens were obtained from 601 cases belonging to different age groups. Sterile Dacron swabs and gargle residue were first streaked on the side of a 5% sheep blood agar plate to which a 0.04 U bacitracin disk had been applied, and then 1.25 mg trimethoprim and 23.75 mg sulphamethoxazole were added to the plate. After incubation, beta-hemolytic colonies were classified serologically by latex agglutination. GAS was detected in both throat swabs and throat gargle specimens in 49 cases, but GAS was also detected in 12 throat swabs from patients with culture-negative gargles and in 8 gargle specimens from subjects in whom throat swabs were culture negative. The strength of agreement was evaluated by calculating the kappa coefficient (K = 0.82, P = 0.000). The sensitivity, specificity, positive predictive value, and negative predictive value of throat gargle specimens were 80.3, 98.5, 85.9, and 97.8%, respectively. Although the conventional throat swab culture remains the gold standard, the throat gargle method is a quick, safe, and easy method for detection of GAS that serves as an effective alternative to throat swab culture.