NEW YORK (Reuters Health) – Many people mistakenly believe that oral sex is safe, unaware that they can readily catch or pass on syphilis in this manner, according to a report put out by Centers for Disease Control and Prevention.Moreover, syphilitic sores in the mouth may in turn increase the risk of HIV infection.

Dr. C. Ciesielski and colleagues from the Chicago Department of Public Health found that syphilis is increasingly being spread through oral sex.

“Persons who are not in a long-term monogamous relationship and who engage in oral sex should use barrier protection (e.g., male condoms or other barrier methods) to reduce the risk for sexually transmitted disease (STD) transmission,” the team advises.

Ciesielski’s group saw that patterns of syphilis transmission changed substantially over the period from 1998 to 2002. During the 1990s, they report in the CDC’s Morbidity and Mortality Weekly Report, syphilis occurred almost exclusively among heterosexuals. Since 2001, men who have sex with men account for nearly 60 percent of people with syphilis.

To account for these findings, they began interviewing persons with syphilis during 2000 to 2002. In almost 14 percent of cases, oral sex was the subjects’ only sexual exposure during the time they were infected; this was reported by 20 percent of gay men with syphilis, and 6 to 7 percent of heterosexual men and women.

These figures don’t include possible infection through oral sex when sexual intercourse also took place.

People with syphilis in the mouth may not have any symptoms, or the sores may be mistaken for aphthous ulcers or herpes, the authors point out.

The lesions may carry high concentrations of the germ that causes syphilis, and are thus highly infectious. Also, oral lesions may increase the risk of being infected with HIV.

“These data underscore the need for educating sexually active persons regarding the risk for syphilis transmission through oral sex,” the investigators write.