The onset of ARF occurs most frequently in children aged five to 14 years. Under the age of five, the child's immune system is not sufficiently mature to generate autoimmune conditions; ARF is rarely seen in children under three. Peak incidence of first episodes of ARF occurs in pre-adolescents; in adulthood it becomes rare again. (6,7) While ARF seems to be associated with ethnicity, there is no identified link to ethnic origin. Genetically, susceptibility occurs in between three and six per cent of all populations. (7)