Antibodies against extracellular products of group A Streptococcus. Diagnostic importance in acute rheumatic fever

Streptococcal throat infection is a sine qua non for the development of rheumatic fever (RF) in genetically susceptible people. Demonstration of such infection is not easy. In overt RF less than 10% of patients still carry streptococci in their throat and immunologic methods are required to identify antibodies against streptococcal products (SP). Humoral response against SP was studied in children and adults with and without RF. Antistreptolysin O (ASO) showed a non-gaussian distribution, and reference value was established as percentile. Adults have a 97 percentile of 227, in children 90 percentile was 451. When RF was present all cases, except one, showed higher values. When antibodies against SP besides ASO were sought by an agglutination test (Streptozyme tm), people below 15 years of age showed low titers in 15 out of 28 cases. In contrast, high titers were the rule in children suffering RF. High ASO titer correlated with high Streptozyme value. These methods are capable to recognize an specific immune response against Group A Beta hemolytic streptococci, and are valuable tools in the diagnosis of RF.