Weekly

November 30, 2012 / 61(47);962-966

Human immunodeficiency virus (HIV) infections attributed to male-to-male sexual contact comprised 64% of the estimated new HIV infections in the United States in 2009 (1). Assessing the geographic distribution of HIV infection by transmission category can help public health programs target prevention resources to men who have sex with men (MSM) in areas where HIV infection from male-to-male sexual contact is most frequent. In 2004, CDC published data on acquired immunodeficiency syndrome diagnoses among MSM and others by metropolitan statistical area (MSA) (2). To examine geographic differences in the prevalence of HIV infection from male-to-male sexual contact among persons aged ≥13 years in the United States and Puerto Rico, CDC estimated the number of HIV infections in persons newly diagnosed in 2010 and analyzed them by transmission category and location. Results indicated that HIV infections attributed to male-to-male sexual contact made up the largest percentage of HIV infections in MSAs (62.1%), smaller metropolitan areas (56.1%), and nonmetropolitan areas (53.7%). Of the 28,851 infections attributed to male-to-male sexual contact, 23,559 (81.7%) were in MSAs, and 11,410 (48.4%) of those infections were in seven MSAs that represented 31.7% (53,169,004 of 167,919,694) of the overall population aged ≥13 years in the MSAs that were assessed. These data support planning for targeted interventions to prevent HIV acquisition and transmission by male-to-male sexual contact among MSM, particularly in those areas most affected.
HIV infections in persons newly diagnosed in 2010 that were reported to the National HIV Surveillance System through June 2011 were examined from 564 locations, including 103 MSAs, 263 smaller metropolitan areas, and 198 nonmetropolitan areas in the United States and Puerto Rico.* Reported diagnoses of HIV infection for persons aged ≥13 years were tallied, and numbers of diagnoses overall and by transmission category were estimated. Data were adjusted for reporting delays and missing HIV risk factors but not for underreporting (3,4). Because a substantial proportion of persons with diagnosed HIV infection are reported to CDC without an identified risk factor, multiple imputation methods are used to assign transmission categories to those persons whose diagnoses are reported without a risk factor (4). Multiple imputation is a statistical approach in which missing transmission categories for each person are replaced with plausible values that represent the uncertainty regarding the actual, but missing, values (5).
Estimates were calculated for new diagnoses of HIV infection attributed to male-to-male sexual contact, injection-drug use, male-to-male sexual contact and injection-drug use, heterosexual contact, and other HIV risk factors or modes of transmission (e.g., hemophilia, blood transfusion, or perinatal exposure). Transmission categories are assigned, based on the single risk factor (of all identified risk factors) that was most likely responsible for HIV transmission (6,7). An exception is male-to-male sexual contact and injection-drug use, which makes up a separate transmission category. Estimates were not calculated for locations that did not have confidential name-based HIV reporting in place by January 2007 (or had not reported these data to CDC since at least June 2007) to enable the calculation of reporting delays. Excluded were locations in Hawaii, Maryland, Massachusetts, Vermont, and the District of Columbia (6).
Of the estimated 37,934 persons aged ≥13 years with a diagnosis of HIV infection who resided in MSAs in the United States and Puerto Rico during 2010, a total of 23,559 (62.1%) had HIV infection attributed to male-to-male sexual contact; 10,128 (26.7%) had HIV infection attributed to heterosexual contact, 3,070 (8.1%) to injection-drug use, 1,145 (3.0%) to male-to-male sexual contact and injection-drug use, and 33 (0.1%) to other modes of transmission (Table 1). Among smaller metropolitan areas, 3,182 (56.1%) of 5,677 HIV infections were attributed to male-to-male sexual contact, and among nonmetropolitan areas, 1,756 (53.7%) of 3,272 HIV infections were attributed to male-to-male sexual contact (Table 1). Of the 28,851 HIV infections among persons with infection attributed to male-to-male sexual contact overall, 23,559 (81.7%) were among persons living in MSAs. Persons aged ≥13 years living in MSAs comprised 65.5% (167,919,694 of 256,388,562) of the total population† of persons aged ≥13 years for the areas that were assessed (103 MSAs, 263 smaller metropolitan areas, and 198 nonmetropolitan areas).
A total of 11,410 (48.4%) of the 23,559 estimated HIV infections attributed to male-to-male sexual contact were among persons who resided in seven MSAs: New York, New York, New Jersey, Pennsylvania (3,347); Los Angeles, California (2,589); Miami, Florida (1,481); Atlanta-Sandy Springs-Marietta, Georgia (1,059); Chicago, Illinois, Indiana, Wisconsin (1,011); Dallas, Texas (995), and Houston-Baytown-Sugar Land, Texas (928) (Table 2). Persons aged ≥13 years residing in these seven MSAs comprised 31.7% (53,169,004 of 167,919,694) of the total population of persons aged ≥13 years for the MSAs that were assessed. The four largest percentages of HIV infections attributed to male-to-male sexual contact in MSAs were in Los Angeles, California (81.9%), Fresno, California (80.8%), Modesto, California (78.8%), and Oxnard-Thousand Oaks-Ventura, California (78.2%).§

Reported by

Hollie Clark, MPH, H. Irene Hall, PhD, Tian Tang, MS, Shericka Harris, MPH, Anna Satcher Johnson, MPH, Joseph Prejean, PhD, Div of HIV/AIDS Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, CDC. Corresponding contributor: Hollie Clark, hclark@cdc.gov, 404-639-3983.

Editorial Note

The results of this analysis indicate that the majority of HIV infections in newly diagnosed persons aged ≥13 years in 2010 were attributed to male-to-male sexual contact. The percentages of HIV infections attributable to male-to-male sexual contact were higher in MSAs, compared with smaller metropolitan areas and nonmetropolitan areas. Among the MSAs examined, seven accounted for 48.4% of the persons with HIV infection attributable to male-to-male sexual contact. The four MSAs with the largest percentages of HIV infections attributed to male-to-male sexual contact were located in California. These results highlight the disproportionate burden of HIV infection among MSM, who were estimated to comprise approximately 3.9% of the male population aged ≥13 years in 2008 in the United States (8).
The geographic concentration of HIV infection reflects the higher risk for HIV transmission in areas with larger populations, greater prevalence of HIV infection attributed to male-to-male contact (e.g., MSAs compared with smaller areas), and possibly a greater prevalence of MSM living in the community. Effective interventions that could reduce the number of HIV infections in MSAs include HIV testing, HIV care and treatment, and risk-reduction counseling.
The findings in this report are subject to at least three limitations. First, HIV infection surveillance locations in five areas were excluded because they had not had confidential name-based reporting in place by January 2007 or had not reported these data to CDC since at least June 2007. The effect of this limitation is unknown. Second, comparisons were made based on estimated percentages of diagnoses instead of HIV diagnosis rates. To evaluate disparities in HIV risk between groups, HIV diagnosis rates should be calculated by applying population denominators for persons within each transmission category; however, such population estimates currently are unavailable for MSAs, smaller metropolitan areas, and nonmetropolitan areas. Finally, transmission category estimates were adjusted for missing risk factor information. Whether these adjustments introduce any bias in overestimation or underestimation of percentages of HIV infection attributed to specific categories is unknown. Adjusted estimates should be interpreted with caution, particularly when numbers are small (i.e., less than 12).
CDC's High-Impact HIV Prevention¶ program relies on geographic targeting of resources and proven, cost-effective interventions to achieve the goals of the National HIV/AIDS Strategy, which include reducing the number of persons who become infected with HIV, increasing access to care and optimizing health outcomes for persons living with HIV, and reducing HIV-related health disparities.** The results of this analysis underscore the uneven geographic distribution of the burden of HIV infection in MSAs in the United States and Puerto Rico. The geographic disparity in HIV burden also indicates a need to target MSM who bear a large percentage of the burden of infection in areas where persons are at greatest risk for HIV transmission. Health departments, community-based organizations, and other agencies can use these results in planning interventions in their areas to reduce HIV infection and transmission.

References

Prejean J, Song R, Hernandez A, et al. Estimated HIV incidence in the United States, 2006–2009. PLoS One 2011;6:e17502.
CDC. AIDS cases, by geographic area of residence and metropolitan statistical area of residence, 2004. HIV/AIDS surveillance supplemental report. Vol. 12, No. 2. Atlanta, GA: US Department of Health and Human Services, CDC; 2006. Available at http://www.cdc.gov/hiv/surveillance/resources/reports/2006supp_vol12no2/pdf/cover.pdf . Accessed November 21, 2012.
Song R, Green TA. An improved approach to accounting for reporting delay in case surveillance systems. JP Journal of Biostatistics 2012;7:1–14.
Harrison KM, Kajese T, Hall HI, Song R. Risk factor redistribution of the national HIV/AIDS surveillance data: an alternative approach. Public Health Rep 2008;123:618–27.
Rubin, DB. Multiple imputation for nonresponse in surveys. New York, NY: John Wiley & Sons, Inc.; 1987.
CDC. Diagnoses of HIV infection and AIDS in the United States and dependent areas, 2010. HIV surveillance report, 2010. Vol. 22. Atlanta, GA: US Department of Health and Human Services, CDC; 2012. Available at http://www.cdc.gov/hiv/surveillance/resources/reports/2010report/index.htm. Accessed November 21, 2012.
CDC. Terms, definitions, and calculations used in CDC HIV surveillance publications. Atlanta, GA: US Department of Health and Human Services, CDC; 2012. Available at http://www.cdc.gov/hiv/topics/surveillance/resources/factsheets/pdf/surveillance_terms_definitions.pdf . Accessed November 21, 2012.
Purcell DW, Johnson CH, Lansky A, et al. Estimating the population size of men who have sex with men in the United States to obtain HIV and syphilis rates. Open AIDS J 2012;6:98–107.

* MSAs have populations ≥500,000; smaller metropolitan areas have populations of 50,000–499,999, and nonmetropolitan areas are those with populations <50 additional="additional" at="at" available="available" class="cdc-decorated" information="information" span="span">http://www.whitehouse.gov/sites/default/files/omb/assets/bulletins/b10-02.pdf

† Includes populations for adults and adolescents living in seven MSAs that were excluded from the total estimated number of HIV infections attributed to male-to-male contact.

§ Only percentages based on estimated numbers ≥12 are presented.

¶ Additional information available at http://www.cdc.gov/hiv/strategy/hihp/pdf/dhap_policy_maker.pdf

** Additional information available at http://www.whitehouse.gov/administration/eop/onap/nhas