WASHINGTON — Amid ongoing fears of an Ebola outbreak in the United States, Americans got a grim reminder on Tuesday about the ongoing public health threat posed by another deadly virus: HIV.

Seventy percent of Americans who have HIV do not have the disease in check, and many of them are no longer receiving treatment, according to a study published Tuesday.

HIV, or human immunodeficiency virus, causes AIDS, a syndrome that destroys the body’s ability to fight off infections. There are treatments but no cures for HIV/AIDS.

More than a million Americans have HIV, and about 50,000 more become infected every year, according to the U.S. Centers for Disease Control and Prevention, which conducted the study.

The study found that of 1.2 million people who were living with HIV in the United States in 2011, fewer than 3 in 10 had the virus under control. Twenty percent had never even been diagnosed. And about 66 percent of those who had been diagnosed were no longer in care.

Antiretroviral medication can suppress HIV, extending people’s lives and lowering the odds that they’ll pass the disease on to someone else by as much as 96 percent.

“For people living with HIV, it’s not just about knowing you’re infected, it’s also about going to the doctor for medical care,” said CDC Director Tom Frieden in a statement.

“And for health care facilities, it’s not just about the patients in your care – it’s every person diagnosed, and every person whose diagnosis has not yet been made,” he said. “Key to controlling the nation’s HIV epidemic is helping people with HIV get connected to – and stay in – care and treatment, to suppress the virus, live longer and help protect others.”

The CDC’s study also revealed that younger people were more likely not to have HIV under control.

“It’s alarming that fewer than half of HIV-positive young adults know they are infected,” said Eugene McCray, director of CDC’s Division of HIV/AIDS Prevention. “Closing that gap could have a huge impact on controlling HIV – knowing your status is the first critical step toward taking care of your own health and avoiding transmission to others.”