Calculating national rates of HIV infection can quantify the burden of disease and is particularly important for planning and evaluating programs, and guiding resource allocation. HIV incidence measures the number of new infections during a specific time (e.g. year). Estimated HIV incidence rates can be used to assess characteristics of persons most at risk for acquiring HIV infection. HIV diagnoses refer to the number of persons who may have been infected at any time, from years before up to the year when the diagnosis was made. HIV diagnosis rates reflect the trends in HIV incidence and access to HIV testing, and can be used to partially monitor HIV-testing efforts. HIV prevalence refers to the number of persons living with HIV at a given time regardless of the time of infection or whether the person has received a diagnosis. Estimated HIV prevalence rates can be used to monitor the number of persons in need of care and treatment services for HIV infection.
At present, census data are not available to determine HIV rates for different groups at risk of HIV infection such as MSM, person who inject drugs (PWID), or heterosexuals, and such rates are therefore not routinely reported . Using data from national surveys, the Centers for Disease Control and Prevention (CDC) developed an approach to estimate the proportions of the US population classified as MSM, PWID, and heterosexuals, and applied the proportion estimates to census data to produce population sizes for these three transmission categories [2–4]. National HIV infection rates can then be calculated using national HIV surveillance data for the numerators and the population size estimates for the denominators [2–4].
The purpose of this study was to update estimated HIV diagnosis rates [2–4] and, for the first time, to estimate and compare the rates of HIV incidence, for 2010 and 2015 among MSM, PWID, and heterosexuals. The rates of persons living with diagnosed and undiagnosed HIV infection (i.e. HIV prevalence) were also estimated for 2015. These analyses allow cross-group comparisons at different times to inform progress toward meeting the national goal of reducing health disparities .
We calculated three types of HIV rates for persons aged 13 years or older: diagnosis rates in 2010 and 2015; incidence rates in 2010 and 2015; and prevalence rate in 2015. The MSM, PWID, and heterosexual classifications were created to best correspond to the HIV transmission categories presented in the national HIV surveillance report . Transmission category summarizes a person's possible HIV risk factors based on the presumed hierarchical order of transmission probability. Persons with more than one reported risk factor are classified in the category listed first in the hierarchy (for men, male-to-male sexual contact, injection drug use, heterosexual contact; for women, injection drug use and heterosexual contact) . One exception is MSM who inject drugs; this group makes up a separate transmission category .
The numerators: HIV diagnosis, incidence, and prevalence
We used national HIV surveillance system (NHSS) data from all 50 States and the District of Colombia (DC) reported to CDC as of June 2017. All jurisdictions had fully implemented name-based HIV reporting by April 2008. CDC periodically assesses the portfolio of NHSS to determine whether methods and efficiencies in data collection and analysis meet the information needs of the nation. Due to the improvement of data quality over the years, in 2016, CDC determined that the adjustments for reporting delays were no longer necessary . We used data reported through June 2017 for year 2015 to allow reporting of diagnoses and especially deaths, for which 18 months reporting delay is needed to allow time for matching HIV surveillance data with vital statistics data . Some cases of HIV infection were reported to CDC without an identified risk factor . Multiple imputation was used to assign a transmission category .
The number of HIV diagnoses in 2010 and 2015 were the cases reported to NHSS (https://www.cdc.gov/nchhstp/atlas/). The HIV incidence and prevalence were estimated based on a well characterized CD4+-depletion model [8–10]. Because HIV targets CD4+ cells, without treatment, HIV reduces the number of CD4+ cells. Using the first CD4+ cell count after diagnosis and the estimated depletion of CD4+ cells over time, the time between infection and diagnosis can be estimated with the assumption that no treatment has been received . Based on the estimated time from HIV infection to diagnosis, the diagnosis delay distribution can be calculated, which is then used for estimating HIV incidence. Cumulative HIV incidence minus cumulative deaths among persons with HIV yields an estimate of prevalence, the total number of persons with diagnosed and undiagnosed HIV infections . Similar CD4+ models have been used in estimating HIV incidence and prevalence in the European Union/European Economic Area [11,12].
The denominators: estimated population sizes for MSM, persons who inject drugs, and heterosexuals in the United States
We used the previously published estimates of proportions of the US population classified as MSM , PWID , and heterosexuals  (see Appendix A, http://links.lww.com/QAD/B414) to calculate the population sizes for these three transmission categories. The previously published proportion estimates were derived from meta-analyses of national probability surveys across multiple years and were not stratified by year. For our analyses, the proportion estimates were assumed to remain the same for 2010 and 2015. While the proportions of the US population classified as MSM, PWID, and heterosexuals were estimated based on multiple national surveys, the proportion estimate for MSM who inject drugs was only based on a single national survey – National Health and Nutrition Examination Survey (NHANES) . According to the NHANES data from 1999 to 2008, 0.35% [confidence interval (CI) 0.18–0.52] of males aged at least 18 years old were MSM who inject drugs . Due to the limitation of a single survey for estimating the proportion of MSM who inject drugs and the small number of HIV cases among this group, they were excluded from the analyses.
To calculate the population sizes, we applied the proportion estimates for MSM, PWID, and heterosexuals to the population data for 2010 and 2015 obtained from the Vintage 2016 postcensal estimates from the US Census Bureau. The estimated population sizes were used as the denominators for calculating the HIV prevalence rates. For HIV diagnosis rates, the denominators for 2010 and 2015 were calculated by subtracting the number of persons who were living with diagnosed HIV infection at year-end 2009 and 2014, respectively, from the population estimates. For HIV incidence rates, the denominators for 2010 and 2015 were calculated by subtracting the number of persons who were living with diagnosed and undiagnosed HIV infection at year-end 2009 and 2014, respectively, from the population estimates.
Analyses for rates of HIV diagnosis, incidence, and prevalence for MSM, persons who inject drugs, and heterosexuals in the United States
We calculated HIV diagnosis rates in 2010 and 2015 stratified by race/ethnicity and age groups for MSM, PWID, and heterosexuals. For the rates of HIV incidence and prevalence, the race/ethnicity and age-specific stratifications were conducted only for MSM. Relative standard errors were greater than 30%, indicating low reliability of estimated HIV incidence and prevalence rates for the race/ethnicity and age-specific stratifications of PWID and heterosexuals. Thus, we only reported the rates of HIV incidence and prevalence by sex and not by race/ethnicity and age for PWID and heterosexuals.
All rates were calculated per 100 000 population. Uncertainties associated with the estimated numerators and denominators were calculated using the delta method to derive the standard error for calculating the 95% CIs for estimated rates . We also calculated rate ratios to directly compare rates by transmission category, sex, race/ethnicity, and age. For rate ratios, men, whites, and the youngest age group (13–24 years) served as the referent groups. Differences in estimated rates for the years 2010 (referent group) and 2015 were assessed by the z test. Differences were deemed statistically significant at P less than 0.05. For transparent reporting, the percentage of increase or decrease and associated P value were presented.
Estimated HIV diagnosis rates in 2010 and 2015
The estimated HIV diagnosis rates decreased from 2010 to 2015 for all three transmission categories: MSM: 587.8 and 574.7 per 100 000, respectively (−2.2%; P = 0.012); PWID: 52.4 and 34.3 per 100 000, respectively (−34.5%; P < 0.0001); and heterosexuals: 5.5 and 4.1 per 100 000, respectively (−24.5%; P < 0.0001) (Table 1). Rate ratio comparing MSM to PWID was 11 times as high in 2010 and 17 times as high in 2015, whereas rate ratio comparing MSM to heterosexuals was 107 times as high in 2010 and 140 times as high in 2015.
Among MSM, the highest HIV diagnosis rates were among non-Hispanic blacks/African Americans (hereafter referred to as blacks) at both time points, and the rate increased from 2190.5 in 2010 to 2269.2 in 2015 (+3.6%; P = 0.019). The HIV diagnosis rate among Hispanic/Latino MSM also increased (944.1 in 2010 and 995.3 in 2015; +5.4%; P = 0.003). Comparing black MSM to white MSM, the HIV diagnosis rate was about eight times as high in 2010 and nine times as high in 2015. Comparing Hispanic/Latino MSM to white MSM, the HIV diagnosis rate was three times as high in 2010 and four times as high in 2015. MSM who were 25–34 years old had the highest rates of HIV diagnosis at both time points. The HIV diagnosis rates increased from 2010 to 2015 for MSM aged 13–24 and 25–34 years (+4.5% and +18.1%; both P < 0.001), whereas the HIV diagnosis rates decreased for the older age groups (35–44 years: −22.6%; 45–54 years: −7.2%; 55 years and older: −9.8%; all P < 0.01).
Among PWID, the HIV diagnosis rates decreased 35.6% for men (45.0 in 2010 and 28.9 in 2015; P < 0.0001) and 33.1% for women (70.0 in 2010 and 46.8 in 2015; P < 0.0001). The highest rates in 2010 and 2015 were among black PWID. The HIV diagnosis rates decreased in both sexes among black PWID, Hispanic/Latino PWID, and PWID of other races. However, the HIV diagnosis rate increased among white male PWID (+18.7%; P = 0.015). For female PWID, HIV diagnosis rates increased (+15.4%), although this was not found to be statistically significant (P = 0.056). Comparing black male PWID to white male PWID, the HIV diagnosis rate was 17 times as high in 2010 and six times as high in 2015. Comparing black female PWID to white female PWID, the rate was 11 times as high in 2010 and four times as high in 2015. The differences in HIV diagnosis rates in 2010 and 2015 were also narrowing when comparing Hispanic/Latino PWID to white PWID for both sexes. Among PWID by age groups, the diagnosis rates decreased among age groups older than 35 years (all P < 0.001), but remained stable for persons aged 13–24 and 25–34 years for both men and women.
Among heterosexuals, the HIV diagnosis rates decreased 24.4% for both men (3.8 in 2010 and 2.9 in 2015; P < 0.0001) and women (6.9 in 2010 and 5.2 in 2015; P < 0.0001). The highest rates in 2010 and 2015 were among black heterosexuals. Comparing black male heterosexuals to white male heterosexuals, the diagnosis rate was 33 times as high in 2010 and 29 times as high in 2015. Comparing black female heterosexuals to white female heterosexuals, the diagnosis rate was 27 times as high in 2010 and 22 times as high in 2015. With regard to age groups, male heterosexuals aged 35–44 years and female heterosexuals aged 25–34 years had the highest HIV diagnosis rates. The HIV diagnosis rates decreased among all racial/ethnic groups and age groups, except heterosexual men aged 13–24 years who had a stable HIV diagnosis rate.
Estimated HIV incidence rates in 2010 and 2015
The estimated HIV incidence rates in 2010 and 2015 were 605.0 and 583.6 per 100 000 MSM; 43.0 and 32.7 per 100 000 PWID; and 5.0 and 3.8 per 100 000 heterosexuals (Table 2). The rate ratios indicated substantial disparities between MSM and PWID, and MSM and heterosexuals. Comparing MSM to PWID, the HIV incidence rate was 14 times as high in 2010 and 18 times as high in 2015. Rate ratio comparing MSM to heterosexuals was 121 times as high in 2010 and 154 times as high in 2015.
The estimated HIV incidence rate was stable for MSM overall (−3.5%; P = 0.373). However, it decreased among white MSM (−14.1%; P = 0.024). Blacks had the highest HIV incidence rates at both time points, and the incidence rate remained stable (−2.2%; P = 0.747). For Hispanic MSM, the HIV incidence rate increased (+10.6%), although this was not found to be statistically significant (P = 0.201). Comparing black MSM to white MSM, the HIV incidence rate was about nine times as high in 2010 and 10 times as high in 2015. The rate ratio comparing Hispanic/Latino MSM to white MSM was four times as high in 2010 and five times as high in 2015. MSM 25–34 years old had the highest rates of HIV incidence at both time points, followed by MSM who were 13–24 years old. In contrast to the diagnosis rate, the HIV incidence rate decreased among MSM aged 13–24 years (−21.9%; P < 0.01). However, similar to the diagnosis rate, the incidence rate increased among MSM aged 25–34 years (+27.8%; P < 0.0001).
Among PWID, the overall estimated HIV incidence rate decreased (−23.9%; P = 0.03). Comparing female to male PWID, the HIV incidence rates were approximately 1.5 times as high in 2010 and in 2015.
Among heterosexuals, the estimated HIV incidence also decreased overall (−24.7%; P < 0.0001), and for men (−26.5%; P = 0.026) and women (−23.8%; P < 0.0001). Comparing female to male heterosexuals, the HIV incidence rates were approximately two times as high in 2010 and in 2015.
Estimated HIV prevalence rates in 2015
The estimated rates of HIV prevalence in 2015 were 12 372.9 per 100 000 MSM; 1937.2 per 100 000 PWID; and 126.7 per 100 000 heterosexuals (Table 3). The estimated HIV prevalence rate among MSM was six times the rate for PWID and 98 times the rate for male heterosexuals.
Among MSM, the HIV prevalence rates were higher for both black and Hispanic/Latino MSM compared with white MSM. Among all age groups, MSM aged 45–54 years had the highest HIV prevalence rate. Among PWID, the HIV prevalence rate was higher among women than men (rate ratio 1.4). Similarly, the HIV prevalence rate was higher among female heterosexuals than male heterosexuals (rate ratio 1.9).
The analysis is the first to comprehensively examine the national rates of HIV diagnosis, incidence, and prevalence among MSM, PWID, and heterosexuals in the United States. These national HIV rates show the disease burden, relative to the sizes of the populations, providing a more refined picture of HIV epidemic for guiding resource allocation. The analyses of HIV rates for each transmission category at two time points (2010 and 2015) and by subgroups allowed monitoring the progress toward the goal of reducing health disparities. We found that the overall national diagnosis rates decreased between 2010 and 2015 for all three transmission categories and also for several race/ethnicity and age subgroups. The incidence rates decreased among white MSM, MSM aged 13–24 years, PWID overall, and male and female heterosexuals. While the evidence of progress is encouraging, health disparities remain and have widened for some groups.
The estimated rates of HIV diagnosis, incidence, and prevalence presented here quantify the disproportionate HIV disease burden among MSM compared to PWID and heterosexuals. In addition, our data quantify persistent racial/ethnic disparities among MSM. The estimated rates continue to be substantially higher for black and Hispanic/Latino MSM than for white MSM. Only among white MSM did the HIV incidence rate, and also HIV diagnosis rate decrease. The HIV diagnosis rates increased in black MSM and Hispanic/Latino MSM, whereas the HIV incidence rates remained stable for both groups. The number of new infections among Hispanic/Latino MSM has increased between 2010 and 2015 (the estimated numerator) . However, our analyses could not corroborate an increase in the HIV incidence rate when accounting for the adjusted population size (the estimated denominator). It is possibly due to the uncertainty from the estimated denominator that was added to the HIV incidence rate estimate. The increase in the HIV diagnosis rate and decrease in the HIV incidence rate among MSM aged 13–24 years may reflect targeted testing efforts to identify young MSM with undiagnosed HIV . The result of targeted testing efforts is also reflected in the increased percentage of MSM aged 13–24 years living with diagnosed HIV infection . However, MSM aged 25–34 years had increased rates of HIV incidence, and also diagnosis, pointing out an important age group for intensifying prevention, and also testing efforts.
Racial/ethnic disparities are also apparent among PWID. Among both male and female PWID, blacks had the highest rates of HIV diagnosis. Even though the HIV diagnosis rates in black male and female PWID decreased, the rates were still six and four times as high when compared to white male and female PWID in 2015. Among PWID, white men was the only group that showed a significant increased rate of HIV diagnosis. While we found the overall HIV incidence rate among PWID decreased from 2010 to 2015 and was stable when stratified by sex, our analysis did not directly test whether there was a significant increase in the HIV incidence rate among white men due to the relative standard error above 30%, indicating low reliability of the estimated HIV incidence for this subgroup. However, findings from a CDC study conducted in 20 selected metropolitan statistical areas showed a higher percentage of white PWID than Hispanic/Latino and black PWID reported receptive syringe sharing and sharing injection equipment – behaviors that put them at risk for HIV infection . Whites also reported higher rates of misuse of prescribed pain relievers, tranquilizers, stimulants, and sedatives in 2015 than blacks and Hispanics/Latinos . Increased injection of opiates within a network of people who inject drugs might have fueled HIV infections, especially among white male PWID .
The magnitude of racial/ethnic disparities in HIV diagnosis rates among heterosexuals is even larger than the disparities observed in MSM and PWID. HIV diagnosis rates were between 22 and 33 times as high among blacks compared with the rates among whites and between five and seven times as high among Hispanics/Latinos compared with rates among whites. Several individual, social, and structural factors such as risk behavior, relationship dynamic, stigma, health literacy, health insurance coverage, access to care and HIV treatment, and housing status may have contributed to disparities . Additionally, one recent study showed that blacks had a higher number of HIV infections diagnosed between 2010 and 2015 attributed to heterosexual contact with partners previously known to be HIV-infected than other racial/ethnic groups . Many of the infections from partners known to be HIV-infected could have been averted if discordant couples were aware of and were offered effective biomedical and behavioral prevention methods . Continued efforts to promote HIV testing, treatment for HIV-infected partners, and pre-exposure prophylaxis (PrEP) and other prevention services for HIV-negative partners, not only for MSM and PWID, but also for heterosexuals, are needed to further reduce health disparities.
There are limitations to our analyses due to assumptions made when calculating HIV rates and rate ratios. First, we used the previously published proportion estimates derived from meta-analyses of national probability surveys and thus our analyses are also subject to general limitations that come with estimating population sizes as described in detail for each population in the previous publications [2–4]. Second, we applied the same proportion estimates of the US population classified as MSM, PWID, and heterosexuals to 2010 and 2015 census data, thereby assuming that the proportion of each transmission category remained the same over time. Third, HIV incidence and prevalence were estimated based on a CD4+ depletion model that relies on a series of assumptions . Due to low reliability of estimated HIV incidence and prevalence rates for the race/ethnicity and age-specific stratifications of PWID and heterosexuals, the rates of HIV incidence and prevalence by race/ethnicity and age were reported for MSM only. These limitations point out the need of re-assessing the HIV rates and rate ratios when more data become available.
Despite these limitations, our estimated rates of HIV diagnosis, incidence, and prevalence quantify the burden of HIV disease and point out the groups that need intensified prevention and care efforts, using the most recent and available data. The national HIV diagnosis rates decreased overall for all three transmission categories and several race/ethnicity and age subgroups. The incidence rates decreased among white MSM, persons aged 13–24 years, PWID overall, and male and female heterosexuals. However, MSM continue to be disproportionately affected and health disparities remain and have widened for some groups. Blacks continued to have the highest rates of HIV diagnosis among all racial/ethnic groups of all three transmission categories. Continued efforts are needed to strengthen interventions that offer HIV testing, PrEP, and other prevention services for at-risk populations and improve access to HIV treatment, promote medication adherence, and address barriers to clinical care and supportive services for all persons with diagnosed HIV infection.
Study concept: N.C.; study design: all authors; data analysis: N.C., K.L.H.; data interpretation: all authors; drafting of manuscript: N.C.; revision of manuscript: all authors; final approval of manuscript: all authors.
The authors would like to thank Dr Ruiguang Song for statistical consultation and assistance.
Funding: This work was supported by the Division of HIV/AIDS Prevention at the US Centers for Disease Control and Prevention and was not funded by any other organization.
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
Conflicts of interest
There are no conflicts of interest.
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