favours are traded for fish. Prostitution is also widespread.
And the tradition of "wife inheritance" whereby a man marries a newly-widowed woman within his family is also common practice among the Luo people who live in the area.
Before marrying a new husband, a woman is required to have sex in order to "purify" herself from her previous marriage.
Lillian Atieno Ochola, 37, became HIV-positive 14 years ago after she was "inherited", with the virus passed on to her by her second husband. She then passed it on to her son through breastfeeding before realising she was infected.
Since then, she has been trying to warn her neighbours of the dangers. "I’m urging other fellows not to get into such kind of inheritance before being tested," she said, saying that people generally "respond well and some use the advice and get tested."
The Luo, Kenya’s third largest ethnic group, also practice polygamy. And even if it is not openly acknowledged, men often continue to keep lovers hidden away.
The Luo also reject the tradition of circumcision, a practice recommended by the World Health Organisation (WHO) which can reduce the risks of contracting HIV among heterosexual men by 60 percent, studies have shown.
Although treatment is widely available in Kenya -- UN figures show that in 2011, 72 percent of those diagnosed as HIV-positive were being treated with anti-retroviral therapy -- there are still many other obstacles to overcome.
"Today, many of the challenges in combating HIV are socio-economic and cultural rather than bio-medical," said Lawrence Oteng, minister of health in Homa Bay county.
One of the biggest problems is the stigma surrounding those diagnosed with AIDS.
Many are forced to hide their condition and sometimes end up not following their treatment properly.
"We are still fighting stigma," Oteng said.
Accompanied by a village elder, the MSF team arrives at a first house. There they engage in a long drawn-out discussion with a woman, who eventually agrees that her children be tested after admitting that she herself is HIV-positive and undergoing anti-retroviral therapy.
"We try to promote a family-centred approach, that involves them as a family," said Kibira.
"It’s not easy. Some refuse, some become hostile, but if the counselling is good, they usually are very supportive."
Later another man is also persuaded to allow his children to be tested, but refuses to undergo the same test himself.
"The main challenge is getting the men," he said. "A lot of them don’t want to be tested."
Explaining how circumcision can help is also difficult.
In Luo culture, sex is seen as a boost to the planting and harvesting of the land, and the idea of having to give it up -- even if only for time taken to heal after circumcision -- was initially seen in a negative light.
"When the VMC (voluntary male circumcision) started in 2008 or 2009, there was a big resistance from the Luo community," he said. "Circumcision at the time was very low. Now it is steady."
And with the younger generation less attached to such cultural ideas, they could eventually come around, he added.
Since MSF’s door-to-door campaign began in August, some 5,200 people have been tested. And the NGO has set up mobile clinics where people can come to be tested or even circumcised.