ASO titre is useful in diagnosis of ?

Ans. is 'b' i.e., S. pyogenes Positive throat cultures or rapid streptococcal antigen tests for group A streptococcoci are less reliable for antecedent infection capable of producing rheumatic fever because they do not distinguish between recent infection and chronic pharyngeal carriage (as many people are carrier of this bacteria).Antibody tests are the most reliable laboratory evidence of antecedent streptococcal infection capable of producing acute rheumatic fever. The onset of clinical manifestations of acute rheumatic fever coincides with the peak of the streptococcal antibody response.The antibodies used commonly for serological tests are antistreptolysin 0 (ASO), antideoxyribonuclease (Anti-DNAse) and antihyaluronidase.