Public health organizations are reporting success with a program that lets people with sexually transmitted diseases alert their partners via an electronic postcard that they may have been exposed, according to a report by the Reuters Health news agency.

The program began in San Francisco in 2004, but has since expanded to more than a dozen U.S. states. Since 2004, more than 30,000 people have sent nearly 50,000 e-cards to their sexual partners.

Web site users can choose one of six e-cards, type in recipients' email addresses and either send the postcard anonymously or include their own email addresses, Reuters reported. The e-cards also provide recipients with links to STD information and a map of clinics where they can be tested.

The percentage of recipients who click on the e-card links varies by city, according to data published in the online journal PLoS Medicine. Usages ranges from 20 percent in Los Angeles to a high of nearly 50 percent in Idaho.