Proof of protection: condoms limit infection by cervical cancer virus.

Using a condom during sexual intercourse significantly reduces a woman's risk of being infected with the human papillomavirus (HPV) and lessens her chance of developing precancerous growths on the cervix, a new study finds.

While condoms have been shown to limit the spread of AIDS and other sexually transmitted diseases, their effectiveness has been less clear against HPV, a common, sexually transmitted pathogen that infects roughly three-fourths of U.S. adults at some point in their lives.

To assess condom effectiveness, Seattle researchers focused on 82 female college students who had their first sexual intercourse during the study or within 2 weeks before it started. Each participant maintained an electronic diary, documenting whenever she had intercourse and whether she and her partner used a condom. Every 4 months, the women were tested for HPV and underwent a Pap smear to check for precancerous cell growth, says Rachel L. Winer, an epidemiologist at the University of Washington.

The women, who averaged 19 years old at the start of the study, updated their diaries for about 84 months. During that time, 37 became infected with at least one strain of HPV--some with two or more--after having intercourse.

Women who reported condom use less than 5 percent of the time in the previous 8 months were three times as likely to get HPV infection as were women who used condoms every time they had sex, the researchers report in the June 22 New England Journal of Medicine.

No precancerous lesions turned up in regular clinical checkups of women who had always used condoms during sex during the preceding 8 months, whereas 15 such cases occurred in women who used condoms less often in that period.

"This is certainly the most rigorous study to date looking at condom effectiveness in HPV," says epidemiologist Markus J. Steiner of Family Health International, a nonprofit research group in Durham, N.C. Previous studies of HPV infection and condom use typically relied on participants' memories of their sexual practices over several months, he says.

Winer says that previous research had suggested that because the electronic diary guards the participants' privacy, it elicits more-truthful responses on sensitive subjects than do face-to-face interviews.

The Food and Drug Administration recently approved a vaccine (SN: 10/15/05, p. 243) against four common strains of HPV, two of which cause nearly three-fourths of all cervical cancers. But Winer says that since there are more than 100 HPV strains, even after vaccination, "a condom is still a good idea."