Cumulative incidence of rheumatic fever in an endemic region: a guide to the susceptibility of the population?

Aboriginal Australians in northern Australia are subject to endemic infecti on with group A streptococci, with correspondingly high rates of acute rheu matic fever and rheumatic heart disease. For 12 communities with good ascer tainment, the estimated lifetime cumulative incidence of acute rheumatic fe ver was approximately 5.7 %, whereas over the whole population, with less a dequate ascertainment, the cumulative incidence was only 2.7 %. The corresp onding prevalences of established rheumatic heart disease were substantiall y less than the cumulative incidences of acute rheumatic fever, at least in part because of poor ascertainment. The cumulative incidence of acute rheu matic fever estimates the proportion of susceptible individuals in endemica lly exposed populations. Our figures of 2.7-5.7 % susceptible are consisten t with others in the literature. Such comparisons suggest that the major pa rt of the variation in rheumatic fever incidence between populations is due to differences in streptococcal exposure and treatment, rather than to any difference in (genetic) susceptibility.