I searched US Government OGA and this is all I could find:
https://www.hhs.gov/about/agencies/oga/index.html
Office of Global Affairs (OGA)
The United States Department of Health and Human Services’ Office of Global Affairs is the diplomatic voice of the Department of Health and Human Services—we foster critical global relationships, coordinate international engagement across HHS and the U.S. government, and provide leadership and expertise in global health diplomacy and policy to contribute to a safer, healthier world.
Colonel Stanford asked, “Which agency do you work for?”
Mitch Rapp answered, “OGA.”
Stanford knew that OGA meant “Other Government Agency”, an insiders euphemism for the CIA.