Spatial Diffusion of the Human Immunodeficiency Virus Infection Epidemic in the United States, 1985–87

Abstract

We present a geographical analysis of the first 22 months of the Department of Defense's human immunodeficiency virus (HIV) screening program for military applicants. This analysis concerns four HIV epidemic foci in the United States: New York City; Miami, Florida: Houston, Texas; and San Francisco, California. The cartographic analysis, using a novel smoothing algorithm to stabilize county-based rates, highlights the diffusion of the HIV epidemic from areas with relatively high prevalence to areas with relatively low prevalence of antibody to HIV. While there are particularities specific to each region, the diffusion patterns are remarkably consistent: areas closer to an endemic focus experience a slight decline over time, while more distant areas increase. The diffusion process depicted in map sequences demonstrates expansion diffusion in all four areas, while some provide a clear indication of a mixture of expansion and hierarchical processes.

A previous analysis of these data for a fifteen-month period had concluded there was no evidence of a geographic trend in the data. Those conclusions were based on all ages pooled and used multi-state geographic units, making it unlikely that trends in prevalence, which varied by proximity to HIV epicenters, would have been detected. In view of the temporal crossover between the endemic and nonendemic areas' prevalence rates observed in Florida, Texas and California, any spatial analysis of these data using statewide summary rates will obscure the spatial-temporal trends. These data provide compelling evidence for the existence of sub-state level epidemics growing spatially and temporally into areas some miles from the original epicenters. We hope these results will encourage other public health personnel to undertake detailed surveillance of the AIDS and HIV infection epidemics at a unit of analysis small enough to permit quantifying spatial diffusion of this epidemic.

Key Words:

• spatial diffusion
• epidemics
• HIV
• AIDS
• United States

Notes

We acknowledge the help of Peter Gould, The Pennsylvania State University, in the preparation of this paper, and the drafting of Jeanne Warrington, Michael Tidball, Ester DelRosso, and the staff of the George Deasy Cartography Laboratory at Penn State University, for preparing the maps and diagrams for publication. Mary Goldenbaum, Klaus Waibel and Sam DePriest provided data management and programming support. James Damato and Sally Fuller assured the quality of laboratory testing procedures. Michael Zdeb helped in solving some of the early conceptual problems. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.