Rapid antigen diagnostic testing for the diagnosis of group A beta-haemolytic streptococci pharyngitis

Background: It is difficult to make a diagnosis of group A beta-haemolytic streptococci (GABHS) pharyngitis solely on clinical findings. The McIssac scoring system has been recommended as a reliable clinical tool for diagnosis. The rapid antigen detection test (RADT) has been shown to considerably increase the number of patients who are appropriately treated for streptococcal pharyngitis, compared with the use of traditional throat cultures. It also reduces the time to start treatment. We evaluated the diagnostic utility of RADT in comparison with throat swab culture. Methods: Using the McIssac scoring system, RADT and throat swab cultures in those with a McIssac score of 3 or more, we evaluated 165 children (aged 2-15 years) with a clinical diagnosis of pharyngitis. Results: GABHS pharyngitis was confirmed in 41 (24.8%) by throat swab culture and RADT was positive in 39(23.6%). Only in 2 (4.9%) children, RADT was negative but throat swab was positive. The sensitivity of RADT was 89.7% and specificity was 98.4% with a positive predictive value of 94.6%, negative predictive value of 96.9% and diagnostic accuracy of 96.4%. Conclusion: RADT performed was observed to have high sensitivity and sensitivity for the diagnosis of GABHS pharyngitis in contrast to an earlier report from India. Our observations suggest that using RADT as a point-of-care test is reliable and cost-effective and needs to be propagated in Indian settings where facilities for throat swab culture are not routinely available and also because clinical diagnosis based on scoring systems are comparatively less reliable.