The miasma theory of disease went out of style in the 1850s. The discovery that bacteria, rather than vapors emanating from the soil at night, caused illness launched the modern public health profession. In the intervening 150 years, public health practitioners have focused on controlling disease through sanitary infrastructure and educational campaigns.

Despite these great strides, the geography of HIV illuminates the inconvenient truth that relationships between health and place persist. New York and New Jersey, which together are home to 9.3% of U.S. residents, were the site of 22.3% of AIDS cases recorded by the CDC through 2007. Not only do Oregon and Washington have a much smaller population (3.5% of U.S. residents), their burden of AIDS (1.8% of U.S. cases to date) is far lower (Henry J. Kaiser Family Foundation). If miasma isn’t behind these differences, what is?