Early diagnosis of streptococcal pharyngotonsillitis: assessment by latex particle agglutination test

Abstract

Acute pharyngitis is one of the most common diseases in pediatric practice, and the most common bacterial etiology is group A beta-hemolytic streptococcus (GABHS). Correct diagnosis and treatment are primarily of importance to the prevention of non-suppurative sequelae. Rapid tests for detecting the antigen of group A streptococcus are a useful tool for the diagnosis of streptococcal pharyngotonsillitis, due to the speed of results, accuracy and low cost; however, in our country they are little used and have been little studied. The objective of this study was to evaluate the accuracy of a GABHS rapid antigen detection test kit, in comparison with oropharynx swab culture. Children aged 1 to 18 years with clinical diagnoses of acute pharyngitis were chosen at public emergency and private clinical services in Belo Horizonte, Minas Gerais, Brazil, with children being excluded if they had taken antibiotics within 30 days of their consultation. The final sample consisted of 229 patients, each of whom had two oropharynx swabs taken, one for rapid GABHS testing and the other to be sent for culture. We observed sensitivity of 90.7%, specificity of 89.1%, a positive predictive value of 72.1%, a negative predictive value of 96.9% and a positive likelihood ratio of 9.0 for the rapid test used here, compared with culture. The rapid test studied exhibited a good correlation with culture and is, therefore, of great use in clinical practice for detection of GABHS.