In July 2010, President Obama released the US National HIV/AIDS Strategy (NHAS) . One key focus was reducing the number of HIV infections. Benchmarks were set for reducing annual HIV incidence by 25% and reducing the transmission rate by 30% before the end of 2015 . Recently, the White House released an updated NHAS, maintaining the four overarching strategy goals of the NHAS 2015 but establishing new quantitative indicators for 2020 .
Although the original strategy focused on HIV incidence as a primary indicator, the updated NHAS has abandoned HIV incidence in favor of new HIV diagnoses, reasoning that HIV incidence was too untimely, resource intensive, and inconsistent (due to changing test technologies) to reliably measure progress [2,3]. Indeed, the most recent US HIV incidence estimates from Centers for Disease Control and Prevention (CDC) are for the year 2010 . The updated NHAS also dropped the transmission rate indicator as its calculation requires HIV incidence data.
We believe this to be an unfortunate development as the number of new HIV diagnoses annually is not a good proxy for annual HIV incidence. Incidence and diagnoses are the same only if there is near perfect serostatus knowledge and near immediate diagnosis after infection; unfortunately this is not the case in the USA. Further, that transmission rate monitoring was also dropped only makes it more difficult to adequately monitor progress towards reducing HIV infections, because transmission rates convey how quickly the virus is spreading through the population.
We offer a simple approach, based in basic epidemiology, to provide HIV incidence and transmission rate estimates derived from published CDC data [5,6]. Using the most recent CDC epidemiologic data, we determined annual HIV incidence via the formula:
Current year HIV incidence = [(current year HIV prevalence – previous year HIV prevalence) + current year all-cause mortality among persons living with HIV (PLWH)].
From the annual HIV incidence estimates, we were able to estimate HIV transmission rates (defined as the mean annual HIV transmissions to HIV seronegative individuals by 100 PLWH). Transmission rates were calculated as [(current year HIV incidence estimate/current year HIV prevalence) × 100].
Table 1 displays our input parameters and results. Available prevalence and death information from CDC allows incidence and transmission rate estimates for 2008 through 2012. We estimate that there were 40 698 new HIV infections in the USA in 2008; 38 066 in 2009; 37 253 in 2010; 36 458 in 2011; and 35 958 in 2012. The HIV transmission rate estimates seemingly declined from 2008 (3.56) to 2012 (2.95).
The above analysis provides the first US HIV incidence estimates for the years 2011 and 2012. Our incidence estimates for 2008–2010 differ somewhat with published CDC incidence estimates, which were based on the serologic testing algorithm for recent HIV seroconversion (STARHS) method, and yielded an incidence of 47 500 in 2008; 45 000 in 2009; and 47 500 in 2010 . This difference is likely multifactorial. First, different methodologies are used. The STARHS methodology used an immunoassay that classified new diagnoses as either recent or long-standing, and then employed complex statistical modeling . Our methodology employs CDC prevalence estimates and reported deaths among PLWH. Second, there is uncertainty around input parameters in both approaches. CDC incidence estimates rely upon data collected in 18 states and two cities . Our simplified estimation relies on the level of accuracy of HIV prevalence and all-cause mortality statistics, which incorporate HIV surveillance data from all 50 states and the District of Columbia [5,6]. These differences alone could account for incidence estimate discrepancies.
If the STARHS method indeed provides a more reliable incidence estimate than our simplified methodology, then we must be more discerning about the accuracy of published HIV prevalence and/or death statistics. We must also consider that trends over time are likely more reliable signals than the absolute numbers, which are quite difficult to obtain.
We cautiously note that there may be an overall slow, monotonically downward trend in HIV incidence and transmission rates in the USA, which differs slightly from recent CDC incidence estimates that show no overall decline . Table 1 would indicate that from 2010 through 2012, HIV incidence declined 3.5% (NHAS 2015 goal of 25% reduction), and HIV transmission declined 6.3% (NHAS 2015 goal of 30% reduction). Again, the level of precision in our estimates in Table 1 is reliant on the level of precision in CDC's published prevalence and death statistics.
We offer these simplified estimates in the absence of more complete estimates from CDC, and hope that these estimates spur further discussion about the importance of incidence and transmission rates as key NHAS indicators.
Conflicts of interest
There are no conflicts of interest.
1. The White House Office of National AIDS Policy. National HIV/AIDS Strategy for the United States. 2010.
2. The White House Office of National AIDS Policy. National HIV/AIDS Strategy for the United States: Updated to 2020. 2015.
3. Holtgrave DR, Greenwald R. A SWOT Analysis of the Updated National HIV/AIDS Strategy for the U.S., 2015–2020
. AIDS Behav
6. CDC. Monitoring Selected National HIV Prevention and Care Objectives by Using HIV Surveillance Data – United States and 6 Dependent Areas – 2012. HIV Surveillance Supplemental Report 2014, 19 (No. 3). http://www.cdc.gov/hiv/library/reports/surveillance
. [Accessed 15 Aug 2015]