Scientists at McGill University, reporting in the journal Epidemiology, say they detected the virus in 64% of couples who reported engaging in vaginal sex for a median of 3.9 months.
In 41% of 263 college couples studied, both partners had the same type of HPV, a surprising finding “far more frequent than [the 11%] expected by chance” even though the virus is the most common sexually transmitted infection, the authors write.
“[D]etection of the same type in persons initiating a sex relationship would be rare given type-specific prevalence rates,” says the study, whose lead author is Ann N. Burchell, PhD, of the division of cancer epidemiology, departments of oncology and epidemiology and biostatistics at McGill University in Montreal.
Along with colleagues from the University of Montreal, Burchell and Eduardo Franco, DrPH, MPH, director of McGill’s Cancer Epidemiology Unit, analyzed self-reported data from partners of 263 couples.
The women, college students between 18 and 24, enrolled in the study with their male partners. Women were sexually active with their male partners for no more than six months. Most used condoms, but 9% never used condoms. Self-collected vaginal swabs and clinician-collected swabs from the penis and scrotum were tested for 36 strains of HPV.
Among 169 couples for whom at least one partner was infected, the scientists identified 583 type-specific HPV infections. Twenty-five percent of monogamous partners had the same virus type after engaging in vaginal sex for less than two months, the authors write.
That rose to 68% among those who’d been having sex for five to six months.
“Due to its sexually transmitted nature, the study of HPV at the level of sexual partnership is fundamental to our understanding of the epidemiology of these infections,” the researchers write. “The observation that HPV occurs more commonly in sexual partners than expected by chance provides evidence for the sexual transmission of HPV.”
Transmission is likely early in sexual relationships, and having a new sex partner is an important risk factor for infection in both women and men, the researchers write.
HPV causescervical cancer, as well as cancers of the vulva, vagina, anus, penis, and head and neck. HPV also causes genital warts. Although HPV infections are extremely common, with at least 50% of sexually active women and men contracting this type of infection at some point, most have no symptoms and clear the infection on their own, according to the CDC.
Another article from the researchers using data from the same group of participants was published in the January 2010 issue of the journal Sexually Transmitted Diseases.
The second analysis found that the greatest risk factor for genital HPV infection was infection in a person’s current sexual partner. Condoms were tied to a more protective effect for men than for women.
“These results build on our knowledge that HPV infection is very common among young adults, and underline the importance of prevention programs for HPV-associated diseases,” Burchell says in the McGill news release. “Our results also suggest that HPV is an easy virus to get and to transmit.”
Francois Coutlee, MD, a professor at the University of Montreal’s department of microbiology and immunology and co-author on both articles, says the results suggest that many HPV transmissions occur at the start of new relationships, “which reinforces the need for prevention.”