Are all recurrences of "pure" Sydenham chorea true recurrences of acute rheumatic fever?

We are conducting prospective studies of patients in Santiago, Chile, who have had an attack of rheumatic fever and are receiving continuous secondary prophylaxis with monthly injections of benzathine penicillin G. Throat cultures are obtained just prior to injection each month, and serum antistreptococcal antibody titers (antistreptolysin O and antideoxyribonuclease B) are performed at least every 3 months. During the course of these studies we have observed 17 recurrences of "pure" chorea in 10 patients (six girls). In four recurrences the timing of serologic studies and onset of chorea appeared to exclude the occurrence of an immunologically significant group A streptococcal infection within the preceding 6 to 9 months. In one case the period of serologic follow-up was too brief to allow a definite determination. In the remaining 12 recurrences serologic evidence was suggestive or confirmatory of recent streptococcal infection; however, in several instances the titer elevations were quite modest. Our data suggest that in certain chorea-prone patients, Sydenham chorea may recur after streptococcal infections too weak and transient to be readily detectable or, alternatively, after stimuli other than streptococcal infection.