The use of rapid antigen testing and matrix-assisted laser desorption/ionization-time of flight mass spectrometry in the diagnosis of group A beta-hemolytic streptococci in throat swab samples

Rıdvan Deni̇z,Ayşe Bariş,Banu Bayraktar,Elif Aktaş

doi:10.3906/sag-1712-101

Abstract

Background/aim: We aimed to evaluate the efficacy of a rapid antigen test in detecting group A beta-hemolytic streptococci (GAS) in throat samples in comparison with the culture method and to compare the efficiency of matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and traditional methods in identifying GAS in cultures. Materials and methods: A total of 3668 throat samples from patients with a prediagnosis of tonsillopharyngitis were assessed by the QuickVue+Strep A antigen test and culture. For GAS identification from cultures, bacitracin sensitivity, PYR, and latex agglutination tests and MALDI-TOF MS were used. Results: A total of 567 (15.5%) and 536 (14.6%) of the samples were positive for GAS culture and rapid antigen testing, respectively. The sensitivity and specificity of the rapid antigen test compared to culture was 89.07% and 99%, respectively, while positive and negative predictive values were 94.22% and 98.02%. Traditional methods were in full concordance with MALDI-TOF-MS for all 567 isolates. In all densities of growth in culture, the time to diagnosis with MALDI-TOF MS was significantly lower than with traditional identification tests. Conclusion: This study shows that both the rapid antigen testing of samples and bacterial identification with MALDI-TOF MS contribute much to the rapid diagnosis of GAS tonsillopharyngitis.

Highlights

Group A beta-hemolytic streptococci (GAS) are important pathogens that cause tonsillopharyngitis and more severe infections such as septicemia, pneumonia, or meningitis [1]
A total of 567 (15.5%) and 536 (14.6%) of the samples were positive for GAS culture and rapid antigen testing, respectively
The sensitivity and specificity of the rapid antigen test compared to culture was 89.07% and 99%, respectively, while positive and negative predictive values were 94.22% and 98.02%

Summary

Introduction

Group A beta-hemolytic streptococci (GAS) are important pathogens that cause tonsillopharyngitis and more severe infections such as septicemia, pneumonia, or meningitis [1]. Due to the possibility of the occurrence of complications such as acute poststreptococcal glomerulonephritis and acute rheumatic fever after streptococcal infections, rapid diagnosis and treatment of GAS gains importance [2,3]. Reported sensitivity and specificity rates of rapid tests with regard to culture are 66%–99% and 95%, respectively [4,5,6]. Using a highly sensitive rapid test makes a significant contribution to early diagnosis and appropriate therapy. Rapid antigen tests used to diagnose acute tonsillopharyngitis have resulted in significant reductions in antibiotic prescriptions over the past 10 years [7]

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