The Middlesex-London Health Unit is warning residents who may have had sexual contact with someone they met online or at a swingers party.

Two individuals with syphilis, one who is also HIV positive have been having sex with people they met through Craigslist and at local swingers events.

Dozens of people have potentially been infected.

Syphilis is a sexually transmitted infection (STI) caused by a bacteria that is passed to a male or female partner during any sexual intercourse, such as vaginal, oral or anal sex, and even through deep kissing.

HIV is a virus that can also be spread through any sexual intercourse with someone who is infected. It can also be spread by other means, such as sharing needles or other drug equipment.

“We’ve recently become aware of these cases and that there may be a number of people who are engaging in the kind of high-risk activities that carry a heightened risk for the transmission of STIs like syphilis and HIV,” says Shaya Dhinsa, Sexual Health Manager with the Middlesex-London Health Unit in a news release.

“Because these infections may not be accompanied by symptoms, it is possible those who participate in these activities may already be infected, and therefore could be unknowingly spreading an infection to others. It’s important they see their family physician, or come to the Health Unit, for testing.”

STI testing is available at the Health Unit.