Evidence has been presented which suggests that the true incidence of Rocky Mountain spotted fever is currently much greater than the number of reported cases.
An epidemiological study of Rocky Mountain spotted fever in Virginia has also been described. It was observed that the region with the highest rate of disease was the Piedmont. It was also shown that the suburban areas are high risk localities, with only slightly fewer cases than the rural areas. Abandoned land, either abandoned fields or woodland, as well as small rodent activity, was associated with almost all of the cases studied by means of on-site investigations. Currently or previously infected small mammals were present in the immediate vicinity of case locations investigated and were apparently serving as a reservoir of the infectious agent. The manner in which certain trends in land use combine to increase the tick habitat area was discussed, particularly in regard to recent figures on the abandonment of cropland, increase in hardwood forests, and increase in logging activity.
The evidence presented suggests that the present population growth rate, pattern of settlement, and trends in land use are contributing to an increasing risk of Rocky Mountain spotted fever.
The authors are aware of the limitations of a retrospective analysis of the type presented, with respect to understanding the dynamics of the disease. An ecological study is necessary to determine the interrelationship of the components of the ecosystem in which spotted fever circulates. Such a study is in progress and the results will be reported in a later paper.
Section of Biostatistics, Division of Preventive Medicine, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D. C. 20012.
Bureau of Insect and Rodent Control, Virginia State Health Department, Norfolk, Virginia 23502.
Department of Biology, Old Dominion College, Norfolk, Virginia 23508.