It’s been four years since a clinical trial showed that early treatment of HIV infection can dramatically reduce the chances of HIV transmission. In that time, our nation’s prevention efforts have been transformed to help get many more people with HIV diagnosed and into care, both for their own health and to reduce HIV infections nationwide.

The wisdom of that shift has never been in doubt. But new CDC research published yesterday offers a sharper picture of the incredible impact we could have on the nation’s HIV epidemic if we make progress on this front.

The new study Exit Disclaimer, published in JAMA Internal Medicine, estimates that 91.5 percent of new HIV infections in 2009 were attributable to people with HIV who were not in medical care, including those who didn’t know they were infected. In comparison, less than six percent of new infections could be attributed to people with HIV who were in care and receiving antiretroviral therapy.

Let’s put that another way: according to this research, an astounding nine out of ten new infections could be prevented through early diagnosis and prompt, ongoing care and treatment. Getting to that point won’t be easy, but it’s now clearer than ever that our nation’s current prevention strategies are leading us in the right direction.

Over the last few years, CDC has worked with its partners to reshape prevention efforts in ways that can achieve the greatest possible reductions in new HIV infections. To a significant degree, that has meant prioritizing activities that focus on HIV diagnosis, and linkage to and retention in HIV care.

It all starts with testing, which has long been a central focus of CDC’s prevention efforts. Testing is not just the first step in the HIV care continuum; it is a crucial prevention strategy in its own right. Once people know they have HIV, they are able to take steps to prevent transmission to partners. In fact, this new analysis shows that the transmission rate drops substantially after diagnosis, due largely to a reduction in sexual risk behaviors.

It’s in the area of testing that our country has made some of its biggest recent gains. Just a few years ago, one in four, or 25 percent, of Americans with HIV did not know they were infected. Today it’s down to 14 percent – one in seven. But that’s clearly not good enough. The new study estimates that in 2009, 30 percent of new HIV infections in this country could be attributed to people who weren’t diagnosed.

At CDC, we’re working hard to make testing as simple and accessible as possible and to make it a routine part of medical care. As just one example, we’ve launched a pilot project with pharmacies and retail clinics in 24 of the hardest-hit rural and urban areas, training their staff to offer HIV testing and counseling to members of their communities.

But testing is only the beginning – we need to actually get people into care and help them stay there. The new study finds that people retained in HIV care were half as likely as those who were diagnosed but not in care to transmit their virus; being prescribed HIV treatment further lowered the risk. But other recent data show that only about 40 percent of all people with HIV are engaged in care, with only 30 percent having control of their virus through effective treatment.

CDC has intensified its efforts to help more people reach the point where their virus is suppressed. Just recently, we announced a new $210 million round of funding to community-based organizations that work with gay and bisexual men, African Americans and other communities most affected by HIV. Such funding has long been one of CDC’s signature prevention efforts, and this time it includes much greater emphasis on linking people with HIV to the medical care they need – and helping them receive and stay on treatment. This shift is consistent with changes already made to CDC’s funding to health departments and capacity-building assistance organizations nationwide.

We’re also taking other innovative approaches. For example, our Prevention IS Care campaign helps healthcare providers initiate discussions and incorporate ongoing, brief prevention counseling into their care of people with HIV. We’re also excited about CDC’s new Every Dose Every Day e-learning toolkit. It includes four specific medication adherence strategies that can be delivered by HIV care providers, including medical providers, licensed social workers, HIV case managers, and health educators. Eventually, it will include a mobile app to help people track their medications and understand how their treatment is working for them.

Meanwhile, we’re working to increase awareness and understanding of the benefits of testing and early treatment among people diagnosed with HIV. As part of CDC’s long-running Act Against AIDS campaign, we recently launched HIV Treatment Works, which encourages people with HIV to stay in care and receive treatment for their own health and for the health of their partners.

These findings are a signal of the unprecedented opportunity we have to reduce HIV infections in America. But more than that, they are a call to action: for all of us to work toward a time in which every person with HIV knows of their infection and receives the care they need. If we can get anywhere close to that vision, we can dramatically reduce HIV infections in this country and ultimately help bring an end to HIV in the United States.

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For more on the new analysis, view this 60-second video that provides a brief explanation of the study findings and how they can help focus prevention and treatment efforts where they will have the biggest impact.