Methodology

Data Sources
In June 2008, data requests for the numbers of persons living with HIV (non-AIDS) and AIDS, at any time between January 1, 2006 and December 31, 2006, cross-tabulated by county, age, gender, and race/ethnicity, were sent via e-mail to the HIV/AIDS-surveillance branches within the departments of health in all 50 U.S. states, the District of Columbia, Puerto Rico, and the Virgin Islands for the years 2005, 2006, and 2007. Data from the year 2006 were used unless these data were not available from the states. The request specified that if the department could not provide data at the county level, the department should aggregate the data to a region or state level. (The term region is used generically to refer to an aggregation of more than one county.) E-mail requests were followed up with telephone calls when necessary. If states were unable to fulfill the request, the numbers of persons living with HIV (non-AIDS) and AIDS were obtained from the Centers for Disease Control and Prevention (CDC) HIV/AIDS 2006 Surveillance Report [1].

Prevalence Estimation
The population in each county as reported in the 2000 US census [2] was used as an estimate for the number of persons in each county. For states that provided region or state-level data, the census estimates were aggregated to the same geographic areas.

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