Changing patterns in the incidence of Rocky Mountain Spotted Fever on Long Island (1971-1976).

Clinical data from 124 Rocky Mountain Spotted Fever (RMSF) cases submitted by Long Island physicians and hospitals were compiled for the six-year period 1971-1976. This information was subsequently compared to two parameters: first, the geographic distribution of human cases and rickettsia-infected Dermacentor variabilis (Say), and, secondly, the human population dynamics in Long Island towns since 1950. Despite an overall decline in the rate of suburbanization and population growth, cases of RMSF have increased significantly not only in eastern towns where RMSF has been endemic, but also in well-established western towns where recent population increases have been negligible. Phenomena associated with suburbanization, primarily the association of domestic and sylvan animals and their exposure to infected vector populations, may be instrumental in explaining the increased transmission of RMSF.