Since most people who use America Online's SFM4M chat room are disguised by fake "screen" identities, the San Francisco Department of Health has no names or phone numbers to figure out who might have been exposed to the sexually transmitted disease.
Officials do know that as many as 47 men may have dated after meeting in SFM4M, which stands for San Francisco Men For Men, said Jeffrey Klausner, director of the health department's sexually transmitted diseases division.
The seven men who fell ill said their most recent encounters had been with men they met in SFM4M.
AOL refused to release information about its members who visit the chat room. But it did put Klausner in touch with San Francisco-based PlanetOut, on online service for gays, lesbians and bisexuals.
PlanetOut employees spent two weeks visiting the chat room and warning users about the outbreak.
In the late 1970s and early 1980s, San Francisco had the nation's highest rate of syphilis infection. But cases of disease, which is easily treated with antibiotics if detected early, are at an all-time national low and the disease is one targeted for elimination by the federal government.