More than half of young adults in new relationships were infected with human papillomavirus or HPV, researchers in Montreal have found.

The researchers enrolled 263 women aged 18 to 24 and their new male partners.

'Simply having one infected partner is enough to pose a very high risk for HPV infection.'— Dr. Ann Burchell

More than half of participants, 56 per cent, were infected with at least one type of HPV, and 44 per cent were infected with a type that can cause cancer, project co-ordinator Dr. Ann Burchell of McGill University and her colleagues reported in two separate studies published in the January issues of the journal Epidemiology and the journal Sexually Transmitted Diseases.

The presence of HPV in one partner was the strongest predictor of finding the same strain in the other partner, the team found.

"If one partner was infected with HPV, the other partner's chance of also being infected with the same type increased over 50 times," Burchell said in an email. "One does not need to have many sex partners to get HPV. Simply having one infected partner is enough to pose a very high risk for HPV infection."

Sexually active people should expect to be exposed to HPV at some point, Burchell said.

Prevention critical

Most infections will not cause harm. But since it's difficult to predict when the infection will clear on its own and when it may progress to cancer, vaccination, sex education, condom use, and Pap test screening are critical, she added.

The research trial, called HITCH (HPV infection and transmission in couples through heterosexual activity), focused on couples who had started a sexual relationship in the previous six months. It's thought most HPV transmissions take place early in relationships. Since the infections typically last no more than a year or two, transmissions would be far less common among monogamous couples who have been together for a long time, Burchell said.

Using condoms helped reduce the rate of infection, but even among those who used condoms all the time, more than 40 per cent of those tested were infected, the team found.

Vaccination prevents against four common types of HPV, according to the Public Health Agency of Canada. Approximately 1,450 Canadian women will receive a diagnosis this year of invasive cervical cancer, and about 420 women will die from this disease, Health Canada said.

In the research, new couples were defined as those who had been together for six months or less. Participants filled in questionnaires about their sexual history and provided genital specimens for lab tests of HPV infection.

Eduardo Franco, director of McGill's Cancer Epidemiology Unit, led the continuing study, in collaboration with a team from the University of Montreal Hospital Centre.

The research was funded by the Canadian Institutes for Health Research, with unconditional funding support from Merck-Frosst Canada Ltd. and Merck & Co. Ltd, maker of an HPV vaccine, the Canadian Cancer Society Research Institute and by a Richard H. Tomlinson doctoral fellowship to McGill University.