The Kaiser Family Foundation, a non-profit health organisation, has found that in 2001 roughly 67% of black women with Aids had contracted the virus through heterosexual sex - up from 58% four years earlier.
Government studies in 29 states found that black women comprised roughly half of all HIV infections acquired through heterosexual sex, in men and women, from 1999 to 2002. Medical experts put the sharp increase down to a combination of segregation, social exclusion and social and sexual mores. But some were eager to point out that there is scant empirical evidence to explain the rise.
"Yes, the risk of contracting HIV is highest in the African-American community and there's no question black women are at higher risk compared to other women," Robert Janssen, the director of HIV/Aids prevention at the Centres for Disease Control (CDC), told the New York Times. "But there's a lot we still don't understand."
One of the most plausible explanations is segregation. African-Americans make up 12% of the US population, 42% of all people living with Aids and more than half of all new infections. They are also least likely to have partners of different races.
"A high prevalence of infection in the pool of potential partners can spread sexually transmitted infections rapidly within the ethnic group and keep it there," said Adaora Adimora, an infectious disease physician at the University of North Carolina.
The principal theory as to why this affects women so acutely is because of the high rates of HIV infection among gay and bisexual men, which is six times that of whites and four times that of Hispanics, according to a 2001 CDC report. However, homophobia in the black community causes many men to live on "the down-low" - meaning they have public relationships with women and secret sex with men.
A survey in Los Angeles county in 2001 found that 20% of HIV-positive African-American men said they had had sex with women in the past six months, compared with 9% of HIV-positive white men and 4% of infected Latino men.
"Most women don't even know they're at risk," said Cynthia Davis, an assistant professor at Charles R Drew University told the Los Angeles Times. "They find out when their spouse dies, or when they deliver a sick baby."
The situation, some argue, is compounded by an apparent scarcity of potential black male partners, particularly among the middle classes, which can contribute to black men having a higher turnover of relationships. It also puts more pressure on women to have unprotected sex.
"Many of the women on campus are panic stricken because of the feeling of scarcity," said Beverly Guy-Sheftall, a professor of women's studies at the historically black Spelman College in Atlanta. "I see a lot of problematic sexual decision-making among black women across class and age lines."
The disparities in HIV/Aids infection are dramatic, but mirror other racial disparities in health that are most likely related to poverty and access to affordable healthcare. Black women are far more likely than white ones to get hypertension, diabetes and arthritis.
"When America gets a cold," Joseph Lowery, the president emeritus of the Southern Christian Leadership Conference once said, "black America gets pneumonia".