Rheumatic fever is an inflammatory disease and is caused by your immune system overreacting to the beta-haemolytic streptococcus bacteria. It starts with a bad throat infection (what some people call 'Strep throat infection'). A few weeks later you get sore joints: it could be your knees, elbows or wrists. The soreness comes and goes.
This is a companion discussion topic for the original article at https://patient.info/infections/rheumatic-fever-leaflet