HIV transmission at each step of care continuum in the United States

Preventing new HIV infections is essential to reducing future illness and death due to HIV infection in the United States. Interventions at each step of the care continuum (diagnosis, retention in medical care, prescription of antiretroviral therapy [ART] and viral suppression) have the potential to reduce HIV transmission. Estimates of the number of HIV transmissions arising at each step of the HIV care continuum are essential for policy makers and programs to maximize the allocation of HIV prevention resources, according to the study background.

Jacek Skarbinski, M.D., of the Centers for Disease Control and Prevention, Atlanta, and coauthors estimated the rate and number of HIV transmissions attributed to people at each of five care continuum steps: infected but undiagnosed, diagnosed but not in medical care, retained in medical care but not prescribed ART, prescribed ART but not virally suppressed, and achieved viral suppression. The authors used national databases to estimate rates and transmission numbers in the HIV-infected population in the United States in 2009.

According to study results, there were more than 1.1 million people living with HIV in 2009. Of those, 207,600 (18.1 percent) were undiagnosed; 519,414 (45.2 percent) knew of their infection but were not in medical care; 47,453 (4.1 percent) were in medical care but not prescribed ART; 82,809 (7.2 percent) were prescribed ART but not virally suppressed; and 290,924 (25.3 percent) had achieved viral suppression.

Those individuals who were infected with HIV but undiagnosed and those individuals who were diagnosed with HIV but not in medical care accounted for 91.5 percent (30.2 percent and 61.3 percent, respectively) of the estimated 45,000 transmission in 2009.

Compared with individuals who were HIV infected but undiagnosed (6.6 transmissions per 100 person-years), individuals diagnosed with HIV and not in medical care were 19 percent less likely to transmit HIV (5.3 transmissions per 100 person-years) and individuals who were virally suppressed were 94 percent less likely to transmit HIV (0.4 transmissions per 100 person-years). Men accounted for the most transmissions (86.5 percent).

"In the United States, persons living with HIV who are retained in medical care and have achieved viral suppression are 94 percent less likely to transmit HIV than HIV-infected undiagnosed persons. Unfortunately, too few persons living with HIV have achieved viral suppression. These estimates of the relative number of transmissions from persons along the HIV care continuum highlight the community-wide prevention benefits of expanding HIV diagnosis and treatment in the United States. Improvements are needed at each step of the continuum to reduce HIV transmission. Through stronger coordination of efforts among individuals, HIV care providers, health departments and government agencies, the United States can realize meaningful gains in the number of persons living with HIV who are aware of their status, linked to and retained in care, receiving ART, and adherent to treatment," the study concludes.

Commentary: The HIV Treatment Cascade -- A New Tool in HIV Prevention

In a related commentary, Thomas P. Giordano, M.D., M.P.H., of the DeBakey Veterans Affairs Medical Center, Houston, writes: "Not surprisingly then, the study demonstrates that the steps of the cascade that propel HIV transmission in the United States are delayed diagnosis and inadequate retention in care. However, what is surprising is the magnitude of the effect of those steps: the authors estimate that more than 90 percent of transmissions in the United States can be attributed to undiagnosed HIV and poor retention in care."

"Just as there is no single approach to improving adherence to antiretroviral therapy, there likely will be no single approach to improving linkage to and retention in HIV care. Human behavior and the health care system are too complex," the author continues

"Advancing individuals forward from the beginning to the end of the cascade will place a more challenging population on antiretroviral therapy regimens, and fostering their success might require even more supportive resources. Nonetheless, as demonstrated by Skarbinski et al, the benefits of optimizing treatment to the individual will be magnified on a population basis in preventing new infections," Giordano concludes.