Since most people diagnosed with HIV begin taking the highly effective anti-viral drugs that have become common in the past decade, the number of AIDS cases doesn't reflect trends in infection particularly well. Moreover, it's estimated that a quarter of people living with HIV don't know they're infected.

"It's critical that we not become complacent with this. We must remember the human impact behind these numbers and continue to work to reduce this glaring disparity," said Dr. Ronald Valdiserri, acting director for prevention of HIV at the federal Centers for Disease Control and Prevention, which reported the new data.

The overall rate of diagnosis for the human immunodeficiency virus in the United States remained relatively stable in the past four years. But there was a sharp decline of 5 percent annually among blacks. Still, the rate of diagnosis was 76 per 100,000 among blacks, compared with only 9 per 100,000 among whites.

Two Trends

CDC officials said it appears that at least two trends contributed to the decline in diagnoses among blacks. First, there was a 9 percent annual decline in diagnoses among intravenous drug users, who get the virus by sharing needles. More than half the IV drug users were black, according to Dr. Lisa lee, the CDC's senior epidemiologist for HIV-AIDS.

Also, there was a 4 percent decline in diagnoses among people from heterosexual contact, which accounts for 34 percent of infections overall, but includes more than 46 percent of infections among blacks.

The analysis is based on data from 33 states that conducted confidential, name-based reporting during those years, including, for the first time, New York.

Although federal officials have been tracking the HIV-AIDS epidemic for more than a quarter century, reporting to the CDC is mandatory only when an infection progresses to acquired immune deficiency syndrome.

But since most people diagnosed with HIV begin taking the highly effective anti-viral drugs that have become common in the past decade, the number of AIDS cases doesn't reflect trends in infection particularly well.

Moreover, it's estimated that a quarter of people living with HIV don't know they're infected.

California, Illinois Still Left Out

Adding the information from New York "provides us a much more representative picture of the magnitude of the epidemic in this country," Valdiserri said, noting that the state accounted for 20 percent of all the diagnoses from the states, with the majority of cases concentrated in New York City. Because of varying state reporting and privacy requirements, California and Illinois are among the states still left out of the database.

Lee noted that the decline in diagnoses among IV drug users is consistent with studies that have shown reduced HIV infection rates in communities where programs to ensure access to sterile needles are in place. New York set up a needle exchange program in 1992.

Diagnoses among men who have sex with men remained stable between 2001 and 2003, but increased by 8 percent between 2003 and 2004, a trend that was true for men of all races.

Valdiserri said it's not clear whether the change reflects a real increase of infection rates in this group or is a result of more testing being done, or some combination of both.

CDC officials have noted that infection rates for several other sexually transmitted diseases, including syphilis and drug-resistant gonorrhea, are up among homosexual men, but Valdiserri said since the HIV infection reports don't distinguish how recently an infection may have occurred, the state data has limited value in signaling behavioral changes in high-risk groups.