Knowledge center. Rheumatic fever is an inflammatory disease that may develop as a complication of a streptococcus infection, such as strep throat or scarlet fever (caused by Streptococcus pyogenes or group A beta-hemolytic streptococcus).heumatic fever mainly affects children aged between 5 and 15 years; however, it can affect adults and younger children. Boys and girls have the same risk of developing the disease; girls and women tend to have more severe symptoms. The disease may cause long term effects on the skin, heart, brain and joints.