The number of HIV-positive people living in the United States increased 11 percent from 2003 to 2006, which experts attribute to life-prolonging antiretroviral therapy, Bloomberg News reports.

According to a study published in the October 3 edition of the U.S. Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report, the HIV-positive population rose from an estimated 994,000 in 2003 to 1.1 million in 2006.

A separate study published in The Lancet in July found that combination therapy, introduced in 1996, extended the life expectancy of newly infected 20-year-olds by 13 years. They’re now expected to live, on average, to age 69 (HIV-negative people in the industrialized world generally live to be 80).

The CDC expects HIV cases “to keep increasing over time as treatment prolongs the lives of infected people and new infections outpace deaths,” said Richard Wolitski, acting director of the agency’s Division of HIV/AIDS Prevention.