An investigation into American medical experiments in Guatemala in the 1940s has uncovered "gruesome" new details about how subjects were treated. Doctors repeatedly infected people with sexually transmitted diseases like syphilis, gonorrhea, and chancroid without their knowledge or consent, causing untold suffering and death. The experiments were brought to light last year, prompting an investigation by a presidential commission. The commission's full report is due later this month, but some new details were already released this week. Here, a brief guide to this scandal:

What exactly happened to these people?
Between 1946 and 1948, about 1,300 soldiers, mental health patients, prisoners, and prostitutes in Guatemala were intentionally infected with one or more STDs. None was told what they were being exposed to, and more than 80 people died, though it's not clear if the medical experiments were directly responsible for killing them. The experiments were funded by the U.S. Public Health Service, a federal agency.

What was the point of these experiments?
The Guatemala study was ostensibly done to test the effectiveness of penicillin. But the results were never published in any medical journals, record keeping was "haphazard at best," and standard scientific protocols weren't followed.

How gruesome were these experiments?
Very gruesome. One patient was deliberately infected with syphilis. When she later appeared close to death, doctors "inserted pus from a male gonorrhea victim into her eyes, urethra and rectum," says Donald G. McNeil, Jr., in The New York Times. "Four days later, infected in both eyes and bleeding from the urethra, she died."

Were there other STD studies like this in the U.S.?
Yes. In the infamous Tuskegee experiments, hundreds of black men in Alabama were infected with syphilis, never told about their infections, and left untreated. That dark chapter in medical research, which lasted from 1932 to 1972, was led by Dr. John C. Cutler – the same man behind the Guatemala experiments.

Sources: Guardian, NPR, NY Times, Washington Post