Overall, 21.0% (232,700; 95% CI = 221,200-244,200) of estimated prevalent HIV cases were undiagnosed. The percentage of estimated cases of HIV infection that was undiagnosed varied by demographic and risk factors (Table 1). The difference in the percentage of undiagnosed HIV by sex was small (21.7% for males vs. 19.1% for females). Greater differences were observed by race/ethnicity, age, and transmission category. Whites had a significantly lower percentage of undiagnosed HIV (18.8%) compared with Hispanics/Latinos (21.6%), blacks/African Americans (22.2%), American Indians/Alaska Natives (25.8%), and Asians/Pacific Islanders (29.5%). The youngest age group (13-24 years) had the greatest estimated percentage of undiagnosed HIV (47.8%), and the percentage undiagnosed significantly decreased with age up to age 55 years (Table 1).
By HIV transmission category, cases associated with injection drug use (IDU) had the lowest percentage of undiagnosed HIV, male IDU: 14.5%; female IDU: 13.7%; and male-to-male sexual contact and IDU: 12.1% (Table 1). The highest percentage of undiagnosed HIV (26.7%) was among men with a transmission category of high-risk heterosexual contact (HRHC), defined as reporting heterosexual contact specifically with a person known to have, or to be at high risk for, HIV infection (eg, an injection drug user). The second highest percentage of undiagnosed HIV was among MSM (23.5%). We observed differences in the percent of undiagnosed HIV when risk was stratified by sex and race. In ascending order, the percentage of undiagnosed HIV among male HRHC by race was black/African American male HRHC (25.7%), Hispanic/Latino male HRHC (27.9%), white male HRHC (28.5%), Asian/Pacific Islander male HRHC (33.3%), and American Indian/Alaska Native male HRHC (38.8%; all comparisons to black/African American male HRHC, P < 0.003). In ascending order, the percentage of undiagnosed HIV among MSM by race was white MSM (19.8%), American Indian/Alaska Native MSM (25.0%), Hispanic/Latino MSM (26.3%), black/African American MSM (27.2%), and Asian/Pacific Islander MSM (28.6%; all comparisons to white MSM, P < 0.001). A similar pattern was seen for female HRHC, with white female HRHC having a lower percentage of undiagnosed HIV (18.0%) than Hispanic/Latino female HRHC (20.3%), black/African American female HRHC (22.0%), American Indian/Alaska Native female HRHC (25.0%), and Asian/Pacific Islander female HRHC (30.4%; all comparisons to white female HRHC, P < 0.001).
Rates per 100,000 population were calculated for adults/adolescents living with undiagnosed HIV infection in the United States at the end of 2006. Table 2 displays the estimated rates and 95% CI of undiagnosed HIV infection by race/ethnicity and sex for persons aged 13 years and older. Black/African American males had the highest rate of undiagnosed HIV infection (556.5 per 100,000). The next highest rates were among black/African American females (225.7 per 100,000) and Hispanic/Latino males (201.6 per 100,000). Overall, whites represented the greatest percentage of the adult/adolescent population of the United States at the end of 2006, 69.0% overall, but a lower percentage of estimated living HIV cases (34.6% overall; 39.6% of males and 19.7% of females). The estimated rate of undiagnosed HIV among whites was 42.2 per 100,000. In contrast, blacks/African Americans made up 12.0% of the adult/adolescent population but 46.1% of the estimated persons living with HIV (40.2% of males and 63.8% of females). The estimated rate of undiagnosed HIV among blacks/African Americans (380.3 per 100,000) was 9 times the rate for whites. Similarly, Hispanics/Latinos made up 13.4% of the adult/adolescent population but 17.5% of estimated persons living with HIV (18.4% of males and 15.0% of females). The estimated rate of undiagnosed HIV among Hispanics/Latinos (126.4 per 100,000) was 3 times the rate for whites.
The number of persons in the United States living with HIV infection continues to increase each year. A major factor contributing to this increase is reduced mortality due to the use of highly active antiretroviral therapy among persons diagnosed with HIV.20-23 From 1995 to 1998, the estimated number of deaths among persons with AIDS declined 63%, from 51,670 to 18,82324; from 2002 through 2005, the estimated number of deaths averaged 17,189 per year.25 Additionally, the estimated number of annual HIV infections has remained relatively stable over the past decade,11 and these new infections contribute to the number of persons living with HIV.
The burden of HIV infection, both prevalence and percentage undiagnosed, is disproportionate across population groups. Racial/ethnic minorities made up less than one-third (31.0%) of the adult/adolescent population in the United States at the end of 2006 but accounted for nearly two-thirds (65.4%) of persons estimated to be living with HIV. Blacks/African Americans accounted for slightly less than half (46.1%) of all adults/adolescents living with HIV despite comprising only 12.0% of the population. Each racial/ethnic minority group had a significantly greater percentage of undiagnosed HIV infection compared with whites. Blacks/African Americans had the highest rates of undiagnosed infection, with black/African American men showing the highest rate overall. These findings demonstrate the differential impact of HIV on racial/ethnic populations. Because race/ethnicity is not itself a risk factor for HIV infection, differences in HIV disease burden across population groups are likely due to differences in other factors, including perception of risk and risk behaviors26-28 and relative lack of access to-and utilization of-health care resources, particularly HIV testing and treatment.29-31
We also observed differences in HIV prevalence and percent undiagnosed by behavioral risk factor. Sexual contact is the main behavioral risk for both men and women diagnosed with HIV infection.32 Our analysis found that men with a behavioral risk factor of male to male sex comprise nearly half (48.1%) of the estimated adults/adolescents living with HIV at the end of 2006. Although not precisely known, the percentage of MSM in the general population is estimated to be much lower. Data from CDC's National Survey of Family Growth indicate that among males aged 15-44 years, 3.7% ever had anal sex with another male and the percentage of men who had a male sexual partner in the past 12 months was 2.9%.33 MSM also had a significantly greater percentage of undiagnosed HIV infection (23.5%) compared with the overall percentage undiagnosed (21.0%). Again, there were differences in the percentage of undiagnosed HIV infection among MSM by race, with minority MSM having significantly higher percentages undiagnosed compared with white MSM. A similar pattern was seen in a study among MSM in 5 US cities.27 That study also found 48% of MSM diagnosed with HIV were unaware of their infection, twice the undiagnosed percentage of MSM from our national estimate. This finding is likely due to differences in the analysis populations. Persons whose HIV behavioral risk factor was HRHC made up over one-quarter (27.6%) of estimated prevalent HIV cases. Two-thirds (66.0%) of the estimated living HIV cases attributed to HRHC were among women, with two-thirds of those being black/African American women.
Interestingly, our analysis found that persons exposed to HIV through IDU had significantly lower percentages of undiagnosed HIV infection. This may be the result of injection drug users interacting with the health care system through the use of emergency departments, needle exchanges, drug treatment facilities, or community outreach programs;34-37 in such settings, IDUs may have a greater chance of being offered an HIV test. Also, it may be that injection drug users are more likely to acknowledge their exposure risk for HIV and thus have a greater predilection to accept HIV testing when it is offered.35-38
Our analysis is subject to some limitations. HIV data from the 40 states used in the extended back-calculation model represent only a portion of persons in the United States who are diagnosed with HIV infection. Several high-morbidity areas did not contribute HIV surveillance data, including California, Illinois, Maryland, and the District of Columbia. Thus, the national data on diagnosed cases of HIV infection are incomplete. Additionally, the data presented here have been statistically adjusted to account for reporting delays for new cases and for deaths, and cases reported without risk factor information have been redistributed among other transmission categories. These adjustments are based on assumptions (eg, reporting delays have not changed over time) that may no longer be accurate.12,13
The continued increase in the prevalence of persons living with HIV infection, both diagnosed and undiagnosed, is an ongoing challenge for providing medical and social services. The financial costs of care for persons diagnosed with HIV continue to grow, with most of the care dollars provided by the federal government. The federal budget request for fiscal year 2007 included $13.2 billion for medical care for persons with HIV.39 The discounted lifetime cost for treating a person entering HIV care with a CD4 count less than 350 has been estimated to be $385,000 in 2004, with most of the cost attributed to HIV-related medications.40 That figure reflects the substantial costs associated with treating HIV infection for a projected period of 24.2 years after initiation of antiretroviral therapy. As the number of diagnosed cases of HIV infection increases, those dollar amounts will continue to grow ever larger.
Persons living with HIV infection who are not yet diagnosed are not able to benefit from early monitoring and appropriate treatment of their disease condition, which have been shown to reduce morbidity and mortality.41,42 Persons who are unaware of their positive HIV status are also more likely to engage in HIV transmission risk behaviors compared with infected persons who have been diagnosed: Studies have shown that transmission risk behavior decreases among persons newly diagnosed with HIV infection.7,43,44 Thus, recent national HIV prevention strategies have focused efforts on routinizing HIV testing and working with HIV-positive persons to initiate and maintain HIV risk reduction behaviors, with the goal of reducing new HIV infections in the United States.2,45
The epidemic of HIV infection in the United States is now in its third decade. Better treatments are allowing many infected people to live longer; however, there is still no cure for HIV disease. Despite major advances in the scientific understanding of HIV, development of a safe and effective vaccine against HIV remains elusive.46,47 Thus, prevention will continue to be the main component of HIV disease control activities. Innovative approaches to reduce transmission risk behaviors are needed to decrease the number of new HIV infections. Additionally, new and creative public health programs that include sufficient and sustained funding are necessary to increase the percentage of persons with HIV infection who are diagnosed and provided appropriate care and prevention services.
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