Crisostomo began doing HIV AIDS work in 1985 when he was in New York City. One of his jobs was at a club where many patrons began falling sick. He volunteered to do hospital visits for the terminally ill HIV/AIDS patients. Crisostomo himself contracted HIV in 1987 and was diagnosed with AIDS in 1995.
GAPA Community HIV Project and Asian AIDS Project
In 1992, Crisostomo became an HIV AIDS educator in the Asian Pacific Islanders LGBTQ community through the GAPA Community HIV Project and the Asian AIDS Project, which later merged to become the API Wellness Center. Guam's World AIDS day in 1992 was also the day that Crisostomo became the first Chamorro to publicly come out as living with AIDS. He continued to travel back to Guam and the Pacific area to provide assistance on HIV AIDS capacity building and service provision.
Coral Life Foundation
In 2001, Crisostomo moved from San Francisco to Guam to become the Executive Director of the Coral Life Foundation, a community-based organization working on HIV AIDS in the Asia-Pacific Area. Coral Life Foundation was the first NGO in the area to work on HIV AIDS. In that capacity, Crisostomo convened representatives from the six Pacific Island Jurisdictions which included AIDS directors, program staff, community stakeholders, along with capacity-building assistance providers funded by the Center for Disease Control to discuss the state of HIV prevention and care services in their respective jurisdictions. From these discussions PIJAAG was formed to advocate for the provision of quality HIV prevention and care services and to advise national, international, and local policy entities on HIV AIDS issues within the region. Under Crisostomo's leadership, PIJAAG successful advocacy led to a $600,000 increase in the region's HIV Prevention budget, funding of 3 Planning Grants for Care Services and baseline awards for services to those living with HIV. The Coral Life Foundation closed in 2002 and was replaced with , otherwise known as the .
Crisostomo later became the Executive Director of 7 Sisters, a broad-based alliance of regional Asia Pacific HIV/AIDS networks based in Thailand. He also served as Asia Pacific NGO Delegate from 2009 to 2010.
50-Plus Network
Crisostomo currently facilitates the 50-Plus Network through the San Francisco AIDS Foundation. This network serves the gay, bi, and trans men community members who are 50 years or older in San Francisco through meetings twice a month and social gatherings.