February 15, 2012

Half of New HIV Transmissions Originate From Those Unaware of Their Infections

New mathematical modeling conducted by the U.S. Centers for Disease Control and Prevention and Johns Hopkins researchers underscores how important it is to get all people unknowingly living with HIV in the United States tested and into care. According to a brief report published online ahead of print by the journal AIDS, roughly half of new HIV infections originate with the 20 percent of people living with the virus and are unaware of their infection.

For every 100 people made aware of their positive status, eight transmissions are averted, Irene Hall, PhD, and her colleagues suggest. Even more infections would be averted by ensuring that people who do test positive are linked to and retained in care and are able to keep their viral loads undetectable using antiretroviral therapy. 

“HIV testing is an essential component of a comprehensive strategy to address HIV in the United States,” the authors note. Testing is a necessary step to receiving lifesaving care, counseling and antiretroviral treatment—which in turn effectively reduce the risk of transmitting the virus to others. 

“However,” Hall and her colleagues point out, “about 20 percent of the 1.2 million Americans living with HIV have not been diagnosed and therefore represent missed opportunities for interventions.” 

These missed opportunities proved significant by Hall’s team after plugging HIV prevalence and incidence estimates into a mathematical model. The researchers estimated that 51 percent of transmissions were from people aware of their HIV status, whereas a disproportionate rate—49 percent—were from those unaware they were living with HIV. 

“With about half of HIV transmissions attributed to the 20 percent of persons living with HIV unaware of their infection, decreasing the number of persons unaware of their infections must remain a primary goal of HIV prevention efforts,” Hall’s team comments. 

The authors explained that the CDC recommends routine HIV screening in health-care settings for everyone between the ages of 13 and 64 and at least annual testing for those at increased risk for HIV. 

“However,” they add, “it is equally important that persons diagnosed with HIV are linked to and retained in care, receive risk counseling and, if appropriate, antiretroviral therapy.” While current estimates of the percentage of people diagnosed with HIV who are linked to care are relatively high, the percentage of people who are actually retained in regular care and have undetectable viral loads is much lower. 

“Additional efforts are needed to reduce the number of people unaware of their infection and reach the goals of the National HIV/AIDS Strategy, reduce transmission rates, and improve linkage and retention in care and viral suppression,” the authors conclude.

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