Discussion

The PATH 2.0 model estimated that HIV transmissions in 2016 occurred primarily from persons with HIV infection who did not know they were infected and persons with diagnosed HIV infection who were not in care; together, these two groups accounted for approximately 80% of new infections. Those who were in care but had not achieved viral suppression accounted for approximately 20% of transmissions. To end the HIV epidemic in the United States, the HHS initiative directs a path forward for success (6). First, early detection of HIV infection must be improved (11). Second, once HIV infection is identified, rapid entry into care and prevention services is crucial to ensure achievement of viral suppression as quickly as possible. Modeling studies indicate that viral suppression is critical for decreasing HIV incidence (12).

Providers play an important role in this effort by screening patients for HIV infection, actively linking and engaging persons with HIV infection into ongoing, comprehensive care, and emphasizing the importance of achieving and maintaining viral suppression for personal health and prevention benefits. Routine testing and targeted HIV testing are complementary approaches to addressing the 38% of transmissions that occurred from the estimated 15% of persons with undiagnosed HIV infection, by increasing awareness of HIV infection status and diagnosing infection sooner. Initial diagnosis is a necessary step to obtaining the benefits of HIV treatment and other psychosocial resources; however, the median interval between infection and diagnosis is 3 years (11). CDC recommends routine screening of all Americans aged 13–64 years at least once in their life and at least annual testing for those at high risk for acquiring HIV (13). Providers must work with their patients to ensure that HIV screening occurs in accordance with CDC guidelines. In addition, community partners can provide testing aimed at persons who are less likely to interact with the health care system on a regular basis. Together, these approaches can reduce undiagnosed HIV infection in the United States and thereby decrease transmission from persons with undiagnosed infection.

To address the 43% of transmissions that occur from the 23% of persons who have diagnosed infection and are not in care, improvements in rapid linkage to and retention in care are needed. Continued engagement in care might be difficult for some persons because of barriers that include lack of insurance, housing, transportation, or other resources; stigma and discrimination; mental health and substance use issues; and lack of trust in the medical system (14). These patients can benefit from tailored support services. Research on patterns of care over time could provide a better understanding of factors associated with patient dropout from care (15). Patients might respond well to knowledge of the personal and preventive benefits of treatment. Community efforts to increase public awareness of the benefits of viral suppression might help decrease stigma and make staying in care easier (16).

Helping patients adhere to treatment is important in addressing the 20% of infections that occur from the 11% of persons with HIV infection who are in care but not virally suppressed. Among persons with HIV infection who are in clinical care, approximately 80% were virally suppressed at their most recent visit (17,18), but about one third did not sustain viral suppression over a year (17,18). A tailored approach aimed at the barriers that are most relevant for the patient are important to improving adherence to medications and ultimately achieving and sustaining viral suppression.§

Among population risk groups within the model, most transmissions were from MSM because of the high proportion of persons with HIV infection who are MSM, the higher risk of transmission associated with anal sex, and high HIV infection prevalence among MSM. The highest transmission rate was among persons aged 13–24 years, and the highest number of transmissions were from persons aged ≥55 years, because of the larger number of persons living with HIV infection in this age group.

The findings in this report are subject to at least five limitations. First, PATH 2.0 required data on the sexual and injection behaviors of persons with HIV infection, and such data were limited (e.g., available data often were not stratified by age and disease stage) and mostly based on self-report. Second, although CDC assumed no injection drug use transmissions from persons who were virally suppressed, no data exist on the efficacy of viral suppression in reducing HIV transmission from injection drug use. Third, the model does not account for differences in prevalences of awareness of HIV infection and viral suppression by age. Thus, transmission rate estimates among younger persons might be underestimated, because data show a higher percentage of persons with HIV infection who were unaware of their infection (8) and a lower percentage with viral suppression among the younger age groups (7). Fourth, the model included 23,000 persons to represent the 1.1 million persons with HIV infection in the United States, and, for computational feasibility, the results obtained were scaled up to match current incidence. However, results were similar when a larger number of persons were input into the model. Finally, the model conservatively restricted reductions in transmission attributable to reduced viral load to those who achieved viral suppression. Some data indicate that, in general, persons with lower viral loads have a lower risk of transmission, even in the absence of viral suppression. However, data to determine viral loads over time for persons out of care or with undiagnosed HIV infection do not exist.

Although the prevalence of viral suppression among persons with HIV infection has been increasing, and the number of new infections and transmission rates have been decreasing in the United States, faster rates of change are needed to end the HIV epidemic in the United States. To accelerate progress, persons with HIV infection must receive a diagnosis soon after infection, begin treatment rapidly after diagnosis, adhere to treatment, and receive support services that help achieve and sustain viral suppression. Providers should screen patients for HIV infection at least once and test some patients more frequently; rapidly link, engage, or re-engage patients into comprehensive HIV care; and encourage patients to sustain viral suppression for their own health and because of the tremendous prevention benefits. In addition, many persons with HIV infection find it important to know that maintaining viral suppression prevents sexual transmission to partners, and sharing this knowledge more generally might decrease the stigma associated with HIV infection and help engage patients in consistent care.