Data Methods and Sources

The HIV prevalence data presented on AIDSVu are collected by state and local health departments, and deduplicated and processed by the U.S. Centers for Disease Control and Prevention (CDC) to meet minimum data quality standards for comparability and reliability.

All 50 states, the District of Columbia (DC) and U.S. territories collect comparable confidential, name-based case reports of persons living with an HIV infection diagnosis following standard methods and procedures. Medical providers and other organizations providing HIV testing services are required, by law, to report persons diagnosed with HIV to the state or local health department. Health departments report case data without names to CDC for monitoring of the HIV epidemic on a national scale.

AIDSVu obtained data release agreements from all 50 states, DC and Puerto Rico for the display of state- and county-level HIV surveillance data that are not otherwise publicly released in a national HIV surveillance publication. The data release agreement permitted states to make decisions about the levels of HIV surveillance data they wished to have displayed on the AIDSVu website. All state- and county-level HIV surveillance data for AIDSVu were obtained from CDC's national HIV surveillance database housed in the Division of HIV Prevention's HIV Incidence and Case Surveillance Branch. Data reflected on AIDSVu may slightly differ from data obtained directly from state HIV surveillance programs (e.g., on a state health department website or through a data request) because states may use analysis criteria that are different from what AIDSVu used (e.g., analyzing data by "current residence" versus "residence at earliest HIV diagnosis"). Further, data on AIDSVu may differ from data obtained directly from the states because AIDSVu's data source was CDC's national HIV surveillance database, which contains deduplicated data.

All state- and county-level HIV surveillance data displayed on the AIDSVu maps and state pages reflect persons aged 13 and over living with an HIV infection diagnosis as of December 31, 2008, and reported to CDC through June 2010. Residence at time of earliest HIV diagnosis was used in all geographic analyses. Denominators used to calculate rates for all state and county populations were obtained from official post-2000 census estimates for 2008 from the U.S. Census Bureau. Population denominators are restricted to persons aged 13 and over. There are no counties in DC or Puerto Rico.

AIDSVu allows viewers to look at state- and county-level HIV surveillance data at the overall geographic level, and by sex, race/ethnicity and age groups. Sex was defined as "sex at birth." All race groups are non-Hispanic, and the Hispanic/Latino ethnicity is inclusive of all races. Puerto Rico does not have data displayed by race/ethnicity at the state level because the U.S. Census does not produce post-decennial estimates by race/ethnicity for U.S. territories. Cases were assigned to age groups based on "age at the end of 2008." Caution should be exercised when viewing and interpreting these different maps as the scales change across the different breakdowns and geographic levels; the correct scale is always displayed alongside the map, given the breakdown or geographic level selected.

Rates of persons living with an HIV diagnosis were calculated per 100,000 population to permit data standardization and comparison. Caution should be exercised when interpreting county-level data as these statistics are inclusive of institutional populations (e.g., incarcerated persons, military bases, etc.) and their inclusion may artificially inflate the actual rate and case count of a county when an institution is housed in it. As is standard in the display of health statistics, rates generated from a numerator less than 12 are considered unreliable and should be interpreted with caution. To determine if a specific state or county meets this criterion, click the state or county and a balloon appears and indicates if a rate meets this condition. For rate ratios by race/ethnicity, white race is the referent group.

To protect the privacy of persons living with an HIV infection diagnosis, AIDSVu does not display rates and case counts when the numerator (number of persons living with an HIV infection diagnosis) is less than 5 and/or the denominator (number of people in the state or county in that population group) is less than 1,000. State and counties appear in a shade of gray when one or both of these conditions are met (see footnote below map scale). Because rates are not displayed when the numerator is less than 5, the "unstable rate" indicator mentioned above will only be displayed when the numerator is 5 or greater, but less than 12. Additionally, all rates and case counts on the maps are displayed as ranges, rather than as specific rates, to provide another layer of protection of privacy.

Range intervals were developed using quintiles in SAS analytic software. In order to illustrate the variation in rates and case counts, ranges were developed specific to each geographic level (i.e., states or counties), and for each grouping (i.e., overall, by race, by sex and by age group). Thus, a total of 16 sets of map scales exist (rate/count by state/county by overall/race/sex/age). For each scale calculation, we determined quintiles combining the individual rates or counts for each geographic entity, including all levels of race, sex or age when applicable.

For those states that transitioned to name-based reporting since January 2006 - CA, DE, DC, HI, MD, MA, MT, OR, RI, VT and WA - case counts and rates may be underestimates due to incomplete data and data not yet reported to the surveillance system. Furthermore, AIDSVu is not able to display the "estimated percent of late HIV infection diagnoses" for these states since CDC requires four years of data, adjusted for reporting delays, to display estimated rates reliably.

Los Angeles County, New York City and Washington, DC have zip-code-level data presented on AIDSVu; however, the data were obtained directly from the jurisdictions and not from CDC's national HIV surveillance database as were the state and county data. Because of these different data sources, zip-code-level data are not directly comparable to state and county data displayed on AIDSVu's website. Descriptions of the data methods for zip-code-level data can be found on Los Angeles County's zip-code-level maps, New York City's zip-code-level maps, and the District of Columbia's zip-code-level maps.

Data Sources