New York City remains the "epicenter" of the nation's HIV epidemic, with as many as 4,800 residents contracting the AIDS-causing virus in 2006, according to a new Health Department study citing the most recent available data.

Using a new formula that includes the exact number of HIV diagnoses and estimates of undiagnosed cases, Health Department statisticians concluded there were 72 new infections for every 100,000 people in the Big Apple.

That's more than three times higher than the national average.

As in past studies, gay men and blacks accounted for the bulk of the new infections. Half of all infections were characterized as "men having sex with men," and 46 percent involved African Americans. Blacks and Hispanics accounted for 77 percent of the new infections, overall, the data show.

There are an estimated 100,000 people living with HIV in New York City. Since 2000, the city has averaged between 4,000 and 6,000 new infections a year, with yearly AIDS deaths fluctuating between 1,800 and 2,700.

cbennett@nypost.com