An estimated 1 million people are living with HIV in the United States, and about a quarter of them do not know that they are infected.1 The burden of disease is unevenly distributed among the US subpopulations; blacks and Hispanics comprise about 13% and 14% of the US population, but about 47% and 17% of persons living with HIV/AIDS are blacks and Hispanics, respectively.2 The majority of persons living with HIV/AIDS are men (72%). Lack of knowledge about the risk for HIV infection may contribute to increased risk behaviors for HIV transmission, lack of HIV testing and corresponding awareness of HIV status, and late diagnosis and treatment of HIV. Thirty-nine percent of persons diagnosed with HIV are diagnosed with AIDS within 12 months of HIV diagnosis, and the proportion of blacks and Hispanics diagnosed with AIDS within 12 months of HIV infection is larger than for whites.2
Although previous reports describe the burden of disease in terms of prevalence among population subgroups, estimating lifetime risk may be an additional useful method for assessing the burden of a disease in a population. Moreover, it offers a powerful tool for clinicians, researchers, and policy makers to highlight and communicate more effectively the risk of a disease to nontechnical audiences. Lifetime risk, which is often expressed in terms of the number of people who would need to be followed throughout their lives to observe 1 occurrence of the disease, is more easily understood by the general public. Age-conditional risk estimates allow identification of age categories where the burden of the disease is greatest. Lifetime risk estimates are commonly reported in the popular press and scientific literature for cancer and other diseases. However, there has been little use of the method to estimate the burden of HIV infection. This study estimates lifetime risk and age-conditional risk of being diagnosed with HIV for age, sex, and racial/ethnic subgroups in the 33 states that have had name-based HIV reporting since 2001.
Cross-sectional, age-specific HIV diagnosis, mortality, and population data were used to derive lifetime and age-specific risk estimates of being diagnosed with HIV. Data on HIV diagnoses were obtained from the Centers for Disease Control and Prevention's (CDC's) national HIV/AIDS Reporting System. In 1994, the CDC implemented a uniform system for national, integrated HIV and AIDS surveillance, and 25 states began submitting data to CDC from confidential, name-based HIV reporting systems. Since 2001, data have been available from 33 states (Alabama, Alaska, Arkansas, Arizona, Colorado, Florida, Idaho, Indiana, Iowa, Kansas, Louisiana, Michigan, Minnesota, Missouri, Mississippi, North Carolina, North Dakota, New Jersey, Nebraska, New Mexico, Nevada, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, Wisconsin, West Virginia, Wyoming, and New York). To determine the number of HIV diagnoses (with or without a concurrent AIDS diagnosis) in 2004-2005, we used data for HIV-infected persons from the 33 states reporting HIV diagnosis. The year of HIV diagnosis was based on the earliest reported date of diagnosis.
General and HIV-specific mortality data were obtained from information on death certificates reported to CDC's National Centers for Health Statistics (NCHS) for the 33 states. The most recent NCHS mortality data available were for the year of 2005. The population data for the 33 states were obtained from CDC's NCHS' bridged-race estimates for 2004-2005.3 The bridged estimates are based on the census 2000 counts and produced under a collaborative agreement with the US Census Bureau. These estimates result from converting the 31 race categories used in the census 2000 (1997 standard of the Office of Management and Budget) for the classification of data on race and ethnicity to the 5 categories of the 1977 standard and, therefore, to correspond to the HIV/AIDS data. Our final data consisted of HIV diagnosis data, general and HIV-specific mortality data, and population data from the 33 states during 2004 and 2005.
The numbers of HIV diagnoses and non-HIV mortality during 2004 and 2005 were determined for each 5-year age group. The numbers of HIV diagnoses were adjusted for reporting delay.4 The 5-year HIV diagnosis and non-HIV death rates were derived by dividing the HIV diagnoses and non-HIV death counts in each age group by the population denominator for that age group. These rates were converted to probabilities of a diagnosis of HIV in a given age range, conditional on never having developed HIV before the beginning of the age range, using a competing risks method.5,6 The competing risks were assumed to be independent of the event of interest, that is, HIV diagnosis. The probabilities were applied to a hypothetical cohort of 10 million live births, and estimates were derived for each 5-year age group in the hypothetical cohort of the number alive and HIV-free at the beginning of the interval, the number of newly diagnosed HIV cases in the interval, the number of non-HIV deaths in the interval among the HIV-free population, and the cumulative probability of being diagnosed with HIV from birth. The lifetime risk estimate is the cumulative probability of being diagnosed with HIV from birth. The inverse of lifetime risk renders an estimate for the number of persons who would need to be followed throughout the specified life years to observe 1 HIV diagnosis. Age-conditional risks of being diagnosed with HIV were also computed. Age-conditional risk measures were the probabilities of an individual of a specified age being diagnosed with HIV within a certain number of years, such as the risk of a diagnosis of HIV in the next 10 years among those alive and HIV-free at age 30. Compared with lifetime risk estimates, age-conditional risk estimates are less restricted by long-term extrapolation of the current rates and they provide information for specific ages. Confidence limits were estimated using the generalized gamma method, which used the Taylor expansion as the linear combination of independent Poisson random variables.5 The lifetime risk estimates and age-conditional risk estimates were calculated for the entire selected population and each combination of sex and race/ethnicity. All the calculations were conducted in DevCan 6.2.1 software,6 developed by National Cancer Institute.
During 2004-2005, an estimated 67,898 persons were newly diagnosed with HIV in the 33 states. Overall, the estimated lifetime risk of being diagnosed with HIV was 1.29% (95% confidence interval: 1.28-1.30). To observe 1 HIV diagnosis, 78 infants (95% confidence interval: 77-78) would need to be followed over a lifetime, assuming that the 2004-2005 HIV diagnosis and death rates remain constant over their lifetime.
The estimated lifetime risk of HIV diagnosis for males was 1.87% or 1 in 53 males, and for females, it was 0.71% or 1 in 141 females (Table 1). Among males, non-Hispanic black males experienced the highest lifetime risk, followed by Hispanic males. For black males, the estimated lifetime risk was 6.23% or 1 in 16 black males, whereas for white males, the estimated lifetime risk was 0.96% or 1 in 104 white males. Because case counts were small, confidence limits were wide for American Indians/Alaska Natives and Asians/Pacific Islanders. Black females had a higher estimated lifetime risk (3.29% or 1 in 30 black females) than Hispanic females (0.88% or 1 in 114 Hispanic females) and white females (0.17% or 1 in 588 white women).
Although the lifetime risk of HIV diagnosis increased with age, at every age, males had a higher estimated lifetime risk of HIV diagnosis than females (Fig. 1). Most of the risk of HIV diagnosis was accumulated before the age of 50 years (risk by age 50, 1.51% and 0.58% for males and females, respectively). For example, among males, 81% of the lifetime risk of HIV was accumulated by age 50 (1.51 × 100/1.87 = 81%). More than 50% of the lifetime risk of HIV diagnosis was accumulated between age 30 and 50 (risk of HIV diagnosis by age 30, 0.46% and 0.21% for males and females, respectively).
The estimated 10-year age-conditional risk of an HIV diagnosis for selected ages is shown in Table 2. These numbers indicate the number of persons who would need to be followed for the next 10 years to observe 1 HIV diagnosis among those HIV-free at certain ages-the smaller the number the more likely a diagnosis of HIV will be observed. Among males, those aged 35 years had the highest risk of an HIV diagnosis in the next 10 years (1 HIV diagnosis would be observed among 165 males followed for 10 years), closely followed by those HIV-free at age 30. Among females, those at age 30 had highest risk of HIV diagnosis in the next 10 years. Because the estimates were unstable for American Indians/Alaska Natives and Asians/Pacific Islanders, subgroup analyses for age-conditional risk were only conducted for whites, blacks, and Hispanics. Similar to the results for lifetime risk, blacks had the highest age-conditional risk of HIV diagnosis.
We estimated lifetime risk of HIV diagnosis to present an additional useful method for assessing the burden of HIV disease and to communicate more effectively the risk of HIV disease to nontechnical audiences. Overall, the estimated lifetime risk of HIV diagnosis was approximately 1.29% or 1 in 78 persons. Similar to reports on new HIV diagnoses,2,7 our results show that substantial disparities exist by sex and race/ethnicity, with the estimated risk for males more than 2 times that of females; for black males, more than 6 times and Hispanic males 3 times that of white males; and for black females, 19 times and Hispanic females 5 times that of white females. Black males experienced the highest estimated lifetime risk, 6.23% or 1 in 16 persons. Most of the risk was accumulated by age 50, and those HIV-free at age 30-35 had the highest estimated 10-year age-conditional risk.
Despite some recent declines in HIV diagnoses among blacks and Hispanics,7 they remain disproportionately affected by HIV. Because persons who know they are HIV-infected report reduced risk behaviors, prevention efforts should continue to focus on increased testing and diagnosis and the implementation of proven effective behavior interventions.8,9 In addition, to address the high rates of infection among blacks, CDC has launched the Heightened National Response to the HIV/AIDS Crisis among African Americans, with a focus on expanding the reach of prevention services, diagnosis and treatment, development of new interventions, and the mobilization of communities.10 However, effective prevention interventions need to reach all segments of communities at risk. Among men diagnosed with HIV, a high proportion (about 65% in 20042) are men who have sex with men (MSM) but a small proportion report having been reached by prevention interventions.11
Our analyses are subject to several limitations. First, the estimates are dependent on surveillance data from 33 states and do not represent all HIV diagnoses in the United States. The 33 states included in our analyses comprise about 63% of US AIDS cases, yet some areas that have large populations at risk are not included in the analysis (eg, the District of Columbia and California have large minority populations or the MSM population in California). This could have a potential impact on estimates for subgroups. An assessment of the completeness of case reporting found that more than 80% of AIDS diagnoses and more than 75% of HIV (without AIDS) diagnoses are reported within 12 months after the diagnosis date12; however, persons diagnosed through anonymous testing or persons who have been infected, but have not been tested, are not included. For this analysis, data were only available on HIV diagnoses and not on new infections (incidence). Therefore, the estimates represent the lifetime risk of HIV diagnosis, not HIV infection. In the future, CDC's HIV Incidence Surveillance System may furnish data to determine the lifetime risk of HIV infection. In addition, the small numbers for American Indians/Alaska Natives and Asians/Pacific Islanders limited calculation of age-conditional probabilities for these groups. Finally, because denominator data are not available for risk groups such as MSM or injection drug users, lifetime risk of HIV diagnosis could not be estimated for them.
In summary, sex, age, and racial/ethnic disparities in the risk of HIV diagnosis remain a challenge. As renewed prevention efforts are implemented, these estimates can help improve communication of the risk of HIV diagnosis to specific populations and increase public awareness for HIV. In particular, the high lifetime risk of HIV diagnosis among persons of color and among males, the majority of whom are MSM, can help mobilize these communities to address HIV disease with increased testing and an expanded reach of effective behavior interventions.
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