(CNN) The number of adolescent deaths from AIDS has tripled in the past 15 years despite efforts to curb infections, with the majority of cases reported in sub-Sahara Africa, the United Nations Children's Fund announced Friday.

The UNICEF study found that 26 adolescents are infected every hour, and only one in 10 adolescents in sub-Saharan Africa is tested for HIV.

Girls in the region are disproportionately affected, accounting for seven of 10 new infections among people 15 to 19 years old, the study found.

Many teens who die were infected as infants

"It is critical that young people who are HIV-positive have access to treatment, care and support," Craig McClure, head of UNICEF's global HIV/AIDS programs, said at a conference in Johannesburg, South Africa, where the report was released.

"At the same time, those who are HIV-negative must have access to the knowledge and means to help them to stay that way," McClure said.

Knowledge is power. Know your status. Get tested! https://t.co/XPIAtv4nVK — Voices of Youth (@voicesofyouth) November 27, 2015

Adolescents with the HIV virus are the only infected group for which mortality figures are not decreasing, UNICEF said. Nearly 2 million adolescents from 15 to 19 are living with AIDS, UNICEF said.

Many adolescents who die of AIDS-related illnesses were infected with HIV as infants, at a time when fewer pregnant women and mothers carrying the virus received antiretroviral medications to prevent transmission, the study said. Some of those children have survived into their teens, sometimes without knowing their HIV status, UNICEF said.

"The gains we have made on preventing mother-to-child transmission are laudable and to be celebrated," McClure said. "Immediate investments are needed to get lifesaving treatment to children and adolescents who are infected."

AIDS is No. 1 killer of adolescents in Africa

The report shows that about half of the world's adolescents with HIV live in just six countries: South Africa, Nigeria, Kenya, India, Mozambique and Tanzania.

Infections also continue to occur in Uganda, where Pope Francis is spending the weekend -- and it is a country in which nearly 1.5 million people are living with HIV, according to the latest U.N. data

While visiting Uganda on the second leg of his trip to Africa, Pope Francis met with young people who are living with the virus in the capital, Kampala. He heard their testimony and encouraged them despite the difficulties, to never give up hope.

Some positive news

Despite the setbacks, there has been also progress in the battle with HIV/AIDS.

UNICEF statistics show that since 2000, nearly 1.3 million new infections among children have been averted, largely because of advances in the prevention of mother-to-child transmission of HIV.

At this week's International Conference on AIDS and Sexually Transmitted Infections in Africa, taking place in Harare, Zimbabwe, from Sunday to Friday, scientists and doctors from nearly 150 countries are discussing new recommendations that will enable a faster and more efficient treatment of HIV, including the use of antiretroviral drugs for treatment and prevention.

On Monday, a panel of WHO experts will present updated guidelines, based on new technologies, finds and drugs, aimed at working toward ending the AIDS epidemic in Africa by 2030.

AIDS is the No. 1 cause of death among adolescents in Africa and the second leading cause of death among adolescents globally, according to UNICEF.