The report said that some 30,000 people have used an Internet service that allows then send of alerts to their partners with the click of a mouse.
"This has been an innovative and effective way for us to enable people to communicate with their sex partners," said Dr. Jeffrey Klausner, director of STD prevention and control services at the San Francisco Department of Health.
San Francisco was the first city to have the inSPOT service, which is now in place in Idaho, Louisiana, New York, Oregon, Pennsylvania and Washington. The partner who is exposed to STD risk will get a mail that has "E-card from a concerned friend re: your health via inSPOT" in the subject line.
"We're living in a new world of Internet communication," Klausner said. "Most people are online every day. This Internet communication tool affords people a way to send a message anonymously." Many e-cards warned about gonorrhea, syphilis, HIV and chlamydia.
The details appear in PLoS Medicine.