The U.S. government apologized Friday for a previously unreported experiment that infected hundreds of un-consenting Guatemalans with syphilis in the 1940s.

The research was "clearly unethical," U.S. Secretary of State Hillary Clinton and Health and Human Services Secretary Kathleen Sebelius said in a joint statement. "Although these events occurred more than 64 years ago, we are outraged that such reprehensible research could have occurred under the guise of public health." Contemporary U.S. research standards require informed consent from study participants as well as approval from an institutional review board.

Guatemalan President Alvaro Colom has called the tests "crimes against humanity," BBC News reported.

The research was uncovered by Susan Reverby, a professor of women's and gender studies at Wellesley College. She found that between 1946 and 1948, 696 individuals at the Guatemala National Penitentiary, the National Mental Health Hospital and military barracks in Guatemala were exposed to the sexually transmitted disease (the prisoners via infected prostitutes and the others via direct inoculation). "Permissions were gained from the authorities but not individuals, not an uncommon practice at the time," Reverby noted in a synopsis [pdf] of a forthcoming Journal of Policy History paper on the subject. The individuals were then given penicillin to see if it would cure the disease, but whether it worked on all subjects "is not clear," she wrote in the synopsis.

The Guatemala study was led by John Cutler, a doctor with the U.S. Public Health Service, who was also involved in the infamous Tuskegee syphilis experiment, in which researchers infected hundreds of poor black men in Macon County, Ala., with syphilis to study the disease. The Tuskegee study, which started in 1932, was halted only after newspaper coverage highlighted the experiments in 1972. President Bill Clinton offered a formal apology on behalf of the government in 1997.

Ethics behind any medical research can be tricky, especially when it is being conducted on people from another country or region. "It's still ethically contentious as to how we ought to conduct, or whether we ought to conduct, certain forms of research in poor nations today," Arthur Caplan, a bioethicist at University of Pennsylvania, told the Associated Press.

Other alleged unethical experiments carried out with government backing, such as LSD tests on unwitting U.S. service members and possibly on French civilians, have not been acknowledged by the government. But the latest revelation resulted in a formal apology from Clinton and Sebelius: "We deeply regret that it happened, and we apologize to all the individuals who were affected by such abhorrent research practices." They have promised a thorough investigation into the case.

Image of Treponema pallidum courtesy of Wikimedia Commons/CDC