Comparison of Clinical Findings and Rapid Streptococcal Antigen Detection Test in the Diagnosis of Group A Streptococcal (GAS) Pharyngitis

Abstract

Background: Group A -hemolytic Streptococcal (GAS) pharyngitis is a common illness in children. Diagnosis and proper treatment of group A streptococcal sore throat is important particularly to prevent non-superlative sequel. Clinical findings continue to be used in differentiating streptococcal infection from viral sore throat. Objectives: The aim of this study was to evaluate the accuracy of clinical findings and rapid test in comparison with culture in the diagnosis of group A Streptococcal (GAS) pharyngitis. Patients and Methods: Ninety-four children between 3 to 16 years, who were referred to the pediatric clinic of Rasoul-e-Akram hospital with clinical findings of fever or sore throat were evaluated from October 2006 to May 2007. Clinical findings were recorded and swabs were taken for group A streptococcal cultures and streptococcal rapid antigen detection test. Analysis of statistical significance was performed using the chi-square method. The accuracy of clinical findings and rapid test was compared with the culture method as the gold standard, and sensitivity, specificity, positive predictive values, negative predictive value, positive likelihood ratio (LR+) and negative likelihood ratio (LR-) were calculated. Results: The culture was positive in 38 (40.4%) of the 94 evaluated children. The mean age of children was 8 3.7 years. The presence of petechiae, exudate and Lymphadenopathy (LAP) was more likely in children with positive streptococcus culture and rapid test (P value < 0.05). Lymphadenopathy was known to feature the most sensitivity (100%), specificity (76.8%), and positive predictive value (74.5%), negative predictive value (100%) and positive likelihood ratio (LR) (4.3) among clinical findings. The results of rapid test showed sensitivity of 89.4%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 93.3% in comparison with culture as the gold standard. In general, the accuracy of rapid test was found higher than subjective clinical findings (P = 0.001). Conclusions: Although LAP had good performance in early diagnosis of GAS, a combination of clinical findings, including tonsillar exudates, petechiae with results of rapid antigen test or culture is necessary for clinician judgment. Throat culture is the gold standard test for detecting group A Streptococcal infection, but rapid test is a good replacement for culture.