During the past decade, there has been a significant increase in the proportion of teenagers and young adults engaging in oral sex and, less commonly, having anal intercourse, according to data from STD clinics in Baltimore, Maryland.

The finding is not all that surprising, Dr. Emily Erbelding from Johns Hopkins Bayview Medical Center in Baltimore told Reuters Health.

She explained that "a few national surveys conducted recently have suggested that oral sex may be a behavior that teenagers are increasingly participating in. For example, in the 2002 National Survey of Family Growth, most teenagers reported having oral sex and many had not had intercourse."

She presented the current study findings Tuesday in Jacksonville, Florida at the 2006 National STD Prevention Conference sponsored by the Centers for Disease Control and Prevention.

In examining the 1994 medical records of 2,598 12- to 25-year olds, and the 2004 medical records of 6,438 subjects of the same age, attending STD clinics in Baltimore, Erbelding and colleagues found that over the 10-year period the prevalence of self-reported oral sex in the previous 90 days doubled among males (from 16 percent to 32 percent) and more than doubled among females (from 14 percent to 38 percent).

There was also an increase in rectal sex among young women, "but it was a lot less common than oral sex," Erbelding said. Among young women, the prevalence of self-reported anal sex over the period rose from 3 percent to 5.5 percent.

There may be a general feeling out there that oral sex is safer than intercourse, Erbelding said, and it probably is for some diseases.

However, Erbelding emphasized that oral and anal sex may result in the transmission of STDs that will not be detected in urine tests. "A urine test is not going to pick up gonorrhea or Chlamydia that might have been acquired through rectal or oral sex, with gonorrhea being the more significant infection for oral sex."

Therefore, "clinicians need to routinely ask their adolescent and young adult patients about the full range of sexual behaviors and educate young people in general about what the relative risks are for different types of STDs for various sexual behaviors," Erbelding said.