A 13-year-old boy has had a sore throat for at least a week and has been vomiting for 2 days. his glands are swollen, and he moves stiffly because his joints hurt. his parents, who believe in "natural remedies," have been treating him with various herbal preparations without success and are now seeking antibiotic treatment. throat cultures show infection with group a streptococci. this child is at high risk for