Number one diagnosed by having "Gay Related Immune Deficiency" inside 1982, Callen quickly became a leader in the response to the epidemic, coining the sentence "people with AIDS (PWAs)" inside counterpoint to the so-todays "AIDS victims". He was a initiation member of the Population by using Helps Coalition among more organizations, & he testified prior to the President's Commissiin on Helps & two houses of Congress.

Inside 1983, he co-authored the book Training Use at times Sex inside an Epidemic: A single Approach, which outlined a dogma of safe(r) sex still in utilize in todays world. Inside 1990, he wrote Surviving AIDS, which received an Honorable Mention from either a Western Medical Writers Association.

He was oftentimes seen in television talking all about Helps. Appearances involved Nightline, Skillful Morning Usa, 20/20 & A Phil Donahue Indicate. He wrote for many newspapers & magazines, including a Village Voice, A Future York Native & Outweek; a bit of of his articles come collected within Surviving & Thriving by having Helps, published per Population sustaining Helps Coalition around 1988.

He was as easily the well-loved singer & ballad maker in the gay community. He founded a gay male a cappella singing group, A Flirting, by owning whom he recorded ii albums. He besides experienced the solo album, Purple Heart (Domestic partner Records, 1988), which a read in The Advocate known as, "the most remarkable gay independent release of the past decade." Inside partnership by having Oscar winner Peter Allen and Marsha Melamet, he wrote his most enduring song, "Love Don't Need A Reason", which he sang oftentimes at gay pride and AIDS-related cases around a united states.

Callen died of Helps-related complications inside Los Angeles, California on December 27, 1993. He was 38.