[Effectiveness of rapid antigen test with throat gargle in detecting group A beta-hemolytic streptococci].

OBJECTIVES

The most important disadvantage of rapid antigen tests (RAT) is low sensitivity for the diagnosis of group A beta-hemolytic streptococci (BHS). We determined the sensitivity, specificity, positive and negative predictive values of RAT in gargling samples.

PATIENTS AND METHODS

The study included 106 patients (53 females, 53 males, mean age 22+/-12 years; range 16-65 years) with an initial diagnosis of tonsillopharyngitis. Swab samples were taken from the posterior pharyngeal wall and tonsil surface with a sterile cotton swab. Then, gargle samples were obtained by gargling for 10 seconds with sterile 0.9% NaCl to be examined by the RAT for group A BHS. Throat cultures were processed using standard microbiologic techniques.

RESULTS

Throat cultures were positive in 12 patients (11.3%) and negative in 94 patients (88.6%). Rapid antigen test yielded five positive (4.7%) and 101 negative (95.2%) results. The sensitivity and specificity rates of RAT with throat gargling were 41.7% and 100%, with positive and negative predictive values of 100% and 93.1%, respectively.

CONCLUSION

Despite satisfactory specificity, positive and negative predictive rates of RAT with throat gargling, its low sensitivity limits its use for the diagnosis of group A BHS.