Democrat Obama said he would develop a national strategy to cut down on new infections, expand testing and education, and eliminate the stigma associated with the disease, while his Republican rival McCain vowed to lower drug costs and target testing and prevention in communities most affected.
The Centers for Disease Control and Prevention (CDC) said on Saturday that about 56,300 people were infected with the virus that causes AIDS in 2006, 40 percent more than the previous estimate of 40,000 new infections annually.
"These new figures should bring new focus to our efforts to address AIDS and HIV here at home," Obama said in a statement, advocating "expanding access to testing and comprehensive education programs."
"Combating HIV/AIDS also demands closing the gaps in opportunity that exist in our society so that we can strengthen our public health. We must also overcome the stigma that surrounds HIV/AIDS -- a stigma that is too often tied to homophobia," he said.
"We need to encourage folks to get tested and accelerate HIV/AIDS research toward an effective cure because we have a moral obligation to join together to meet this challenge, and to do so with the urgency this epidemic demands."
McCain pointed out that more than one million Americans live with the disease, and said he would "work closely with non-profit, government, and private sector stakeholders to continue the fight against HIV/AIDS."
"By focusing efforts on reducing drug costs through greater market competition, promoting prevention efforts, encouraging testing, targeting communities with high infection rates, strengthening research and reducing disparities through effective public outreach, we as a nation can make great progress in fighting HIV/AIDS," he said in a statement.
The revised assessment of the epidemic in the United States came on the eve of a six-day international AIDS conference in Mexico City, which is expected to be attended by some 22,000 scientists, policymakers and grassroots workers.
The CDC said new technology allowed it to establish a more precise estimate of the epidemic.
"These data, which are based on new laboratory technology developed by CDC, provide the clearest picture to date of the US HIV epidemic, and unfortunately we are far from winning the battle against this preventable disease," said CDC Director Julie Gerberding.
"We as a nation have to come together to focus our efforts on expanding the prevention programs we know are effective," she said.
The study found that the annual number of new infections was never as low as 40,000. While new infections increased in the last 1990s, they have been roughly stable since then.
The study also found that gay and bisexual men as well as and African American men and women are the groups most affected by HIV.
The new estimate found that 53 percent of new infections occurred in gay and bisexual men, while heterosexuals accounted for 31 percent of them and injection drug users for 12 percent.
African Americans, who make up 13 percent of the US population, accounted for 45 percent of the new infections in 2006. The infection rate among blacks was seven times higher than among whites -- 83.7 out of 100,000 people compared to 11.5 out of 100,000.
The study found some encouraging signs of progress as new infections have dropped among both injecting drug users and heterosexuals.