A 10-year-old boy, the star pitcher for the Salt Lake City Little League baseball team, had a sore throat about 2 weeks ago but did not tell anyone because he was afraid he would miss the play-offs. Since several children have been diagnosed with rheumatic fever in the area, his mother is worried that he may be at risk as well. You tell her that several criteria must be met to make the diagnosis but the most common finding is which of the following?
a) Elevated antistreptolysin O (ASO) titer
b) Positive throat culture for group A β-hemolytic streptococcus
c) Polyarthritis
d) Sydenham chorea