"Between 20% and 25% of HIV infections in young South African women can be attributed to gender-based violence, according to South African and Ugandan research," said Rachel Jewkes from the Medical Research Council.
A report published last month by the World Health Organisation, the Medical Research Council and the London School of Hygiene and Tropical Medicine states that 45.6% of African women have experienced gender-based violence – significantly higher than the world average of 35%.
South Africa has exceptionally high rates of domestic violence: more than 40% of men report having been violent to a female partner, and up to 50% of women report having been victims of this, according to Jewkes's research.
She said the main pathway to HIV infection through gender-based violence was not rape, as many might think. "What's responsible for much more of the new infections is indirect pathways such as the profound psychological impact this violence has on abuse victims, including anxiety, depression, post-traumatic stress disorder and substance abuse."
Jewkes said two things occurred as a result of this psychological distress to increase a battered woman's risk of contracting HIV.
"First, they are more likely to have risky sex, more partners, transactional sex, and are also more likely to end up in sex work," she said.
Psychological distress, according to Jewkes, also makes it much harder for women to protect themselves: "It makes them more likely to accept the man's dominance in the relationship."
She said that once a woman had accepted that she was likely to have more sex more frequently, she was also less likely to use a condom.
"Gender-based violence is responsible for the psychological distress that results in acceptance, which results in more violence and consequently more psychological distress: a cycle of risk and consequence," said Jewkes.
Mbuyiselo Botha, from the gender rights group Sonke Gender Justice Network, said that victims of gender-based violence internalised their experiences as they did not feel as though they could voice their concerns because "they know they are in an environment where they are not respected and their opinions are not taken seriously".
Botha said women felt they could not negotiate condom use, and tended "to accept the status quo due to feelings of helplessness and hopelessness".
He said victims of gender-based violence avoided trying to protect themselves because they feared the violent consequences of voicing their concerns. A woman might be accused, said Botha, of having sexual relations with other men if she asked to use a condom because it was thought she wanted to avoid spreading the diseases she had picked up elsewhere. The logic was that if she had been faithful, there would be no need to use protection. "Violent men always get their way because they know they are feared," he said.
Reproductive health activist Marion Stevens said that HIV was all-pervasive and so was gender-based violence – their roots overlapped.
A 2009 Medical Research Council report co-authored by Jewkes said girls who had been exposed to emotional, sexual and physical violence were at increased risk of later acquiring HIV, as well as depression, suicidal tendencies and substance abuse.
Stevens, who is the co-ordinator of the consultancy group Women in Sexual and Reproductive Rights and Health, said: "If you've been exposed to this abuse from a young age, you might have a poor sensitivity to your own boundaries.
"You might not be able to recognise that future abuse is unacceptable, or have the ability or experience to protect yourself."
She said that "unresolved violence" created a "spiral", and victims might carry this inability to protect themselves into their futures.
According to Stevens, the problem is enhanced because we live in a "very conservative and patriarchal society" where there are few women role models who "embody the right to express oneself in a sexually healthy way".
Another factor that significantly increases these women's chances of becoming infected with HIV is that men who perpetrate gender-based violence are more likely to have HIV themselves.
"Violent and controlling men take more sexual risks and have a higher prevalence of sexually transmitted infections," said Jewkes.
Jewkes said that women who had experienced intimate-partner violence were 50% more likely to contract HIV than women who had nonviolent relationships.
"Clearly, if we want zero new HIV infections, we have to address gender-based violence," she said.