O
A type of clinical trial. In observational trials, researchers do not assign participants to a treatment or intervention. Instead, the researchers observe participants over time to determine health outcomes.
See Related Term(s): Clinical Trial
Contact with a potentially harmful physical, chemical, or biological agent as a result of one's work. For example, a health care professional may be exposed to HIV or another infectious agent through a needlestick injury.
Occupational Post-Exposure Prophylaxis (oPEP) 
(En español)
Short-term treatment started as soon as possible after high-risk occupational exposure to an infectious agent, such as HIV, hepatitis B virus (HBV), or hepatitis C virus (HCV). The purpose of occupational post-exposure prophylaxis (oPEP) is to reduce the risk of infection. An example of a high-risk occupational exposure is exposure to an infectious agent as the result of a needlestick injury.
See Related Term(s): Occupational Exposure
The legal, prescribed use of a drug in a manner different from that described on the Food and Drug Administration (FDA)-approved drug label. Off-label use can include using a drug for a different disease or medical condition or giving a drug at a different dose or via a different route of administration than approved by FDA.
See Related Term(s): Food and Drug Administration
Office of AIDS Research (OAR) (En español)
A federal agency that coordinates the scientific, budgetary, legislative, and policy elements of the NIH AIDS research program.
See Related Term(s): National Institutes of Health
Office of Minority Health (OMH) (En español)
A federal office whose primary responsibility is to improve the health of racial and ethnic minority populations, including African Americans, Hispanic Americans, American Indians, Alaskan Natives, and Pacific Islanders. The Office of Minority Health (OMH) develops or advances policies, programs, and practices that address health, social, economic, environmental, and other factors that impact the health of minority populations, including those specifically affected by HIV/AIDS.
A type of clinical trial. In open-label trials, both the researchers and participants know which drug (or other intervention) is being given to participants.
See Related Term(s): Clinical Trial, Double-Blind Study
Opportunistic Infection (OI) (En español)
An infection that occurs more frequently or is more severe in people with weakened immune systems, such as people with HIV or people receiving chemotherapy, than in people with healthy immune systems.
Optimized Background Therapy (OBT) (En español)
The combination of antiretroviral (ART) drugs most likely to control a person’s HIV. Optimized background therapy (OBT) is chosen on the basis of a person’s resistance test results and treatment history.
Oral Hairy Leukoplakia (OHL) (En español)
A disease of the mucous membranes that occurs mostly in people with HIV. Oral hairy leukoplakia (OHL) is characterized by white or gray lesions that usually develop on the tongue or the inside of the cheek. The lesions have a ribbed, fuzzy appearance. OHL is caused by the Epstein-Barr virus (EBV), a type of herpesvirus.
See Related Term(s): Epstein-Barr Virus
Lower-than-normal bone mass and bone mineral density. Osteopenia often precedes more severe bone loss (osteoporosis). Osteopenia frequently develops in people taking antiretroviral (ARV) drugs; however, the association between ARV drugs and osteopenia is unclear.
See Related Term(s): Osteoporosis
Progressive loss of bone mass and bone mineral density, resulting in an increased risk of fractures. Osteoporosis frequently develops in people taking antiretroviral (ARV) drugs; however, the association between ARV drugs and osteoporosis is unclear.
See Related Term(s): Osteopenia