What must the IRB ensure when studying HIV-positive prisoners?

The correct choice focuses on the importance of maintaining the confidentiality of prisoners' health status, particularly for those who are HIV-positive. This is a critical ethical consideration in research involving vulnerable populations, such as prisoners, who may face stigma, discrimination, or negative consequences if their health information is disclosed.

Ensuring confidentiality helps protect the participants and encourages truthful disclosure during the research process. It is crucial that participants feel safe and secure in sharing their health information without fear of exposure or repercussions. This retention of confidentiality supports the ethical principle of respect for persons, particularly for those in sensitive situations like prisoners living with HIV.

The other options, while they address important aspects of research ethics and participant welfare, do not specifically prioritize the critical issue of confidentiality in the context of HIV-positive prisoners as the selected answer does.