HACKENSACK, N.J. — A 20-year-old diagnosed with HIV or AIDS today can expect to live 50 years  because of groundbreaking advances in treatment since the discovery of the virus 30 years ago.

Despite the progress, troubling trends remain: 47,500 new cases of HIV infection are diagnosed each year in the U.S.

And in the black community, the statistics are even more grim: The virus continues to strike a disproportionate number of blacks, and their death rates are higher than other ethnic groups.

In New Jersey, blacks make up 14 percent of the population but constitute 53 percent of the people living with HIV or AIDS, according to the state Health Department.

“Although we’ve made great strides over the years in reducing transmission of HIV, every day more people become infected,” New Jersey Health Commissioner Mary O’Dowd said last month.

“More than 36,000 New Jersey residents are living with HIV or AIDS, and statistics tells us that too many of them are African American,” O’Dowd said.

Even when there’s good news — a 21 percent decline in the number of new cases nationally among black women in a recent three-year period — it is muted by other statistics — the rate of infection is still 20 times higher for black women than white women.

Meanwhile, new infections among gay and bisexual men between the ages of 13 and 24 were up 22 percent in 2010 compared with 2008. More than half of these were among young black gay and bisexual men, who now account for more new infections than any other subgroup, according to an HIV surveillance report from 2007-10 released by the federal Centers for Disease Control and Prevention in December.