Paying people to take steps to guard themselves against contracting a sexually transmitted infection may be an effective way reduce the spread of these diseases, according to a study presented at the International AIDS Conference in Vienna. The study, the first to examine the use of cash reward to reduce STIs, found that people in rural Africa who were offered up to $60 each over 12 months to stay free of STIs had a 25 percent lower prevalence of those infections after a year compared to those who were not eligible for the money.

Researchers at the University of California, Berkeley, the Development Research Group at the World Bank and the Ifakara Health Institute in Tanzania tested the conditional cash transfer program, an increasingly popular concept in the public health field that essentially rewards desirable behavior with money. Conditional cash transfer programs have been used in several impoverished areas to provide financial incentives to people to do things, such as enroll their children in school or get them vaccinated.

“For many of our study participants, $60 represented about one-fourth of their reported annual income, so it was a significant incentive,” says Will Dow, study author and professor of health economics at the UC Berkeley. “The question we tested is whether the cash reward was enough of an incentive to reduce risky behavior and better take advantage of available health services. Although we cannot directly measure risky behavior, the fact that disease prevalence decreased suggests that the incentives worked.”

The researchers tested the conditional cash transfer program over a one-year period in 10 villiages in southwestern Tanzania. Rates of sexually transmitted infections in the region are comparable to the average rates for Africa, the researchers say.

Most of the study participants ranged in age from 18 to 30 years old, a group considered at high risk for contracting STIs. They were randomly assigned to a no-payment control group, a low-payment group and a high-payment group. Over the year, participants in the low-payment group could get $10 every 4 months–up to $30–if they tested negative for STIs, while those in the high-payment group could get $20 every 4 months, up to $60.

All participants were tested at the start of the study and every four months for the following year to detect a set of curable sexually transmitted infections, including chlamydia, gonorrhea, and syphilis. Individual pre-test and post-test counseling was provided to study enrollees at each testing interval, and monthly group counseling sessions were also made available to all study participants to assist them in their efforts to reduce risky sexual behaviors.

HIV/AIDS was not linked to cash payments for both practical and ethical reasons, but the same risky sexual behaviors that increase the chances of the STIs tested also increase the risk of HIV, the researchers say.

“Cash rewards have been proposed as a new HIV prevention tool to complement traditional approaches,” says Dow. “New prevention tools are desperately needed since five people become newly infected with HIV for every two getting enrolled in new AIDS treatment programs.”

At the end of the trial period, 9 percent of participants eligible for the $60 reward tested positive for the infections compared to 12 percent for the control group who were not eligible for payments. Any participant who tested positive for an STI during the study received free medical treatment and counseling.

The amount of cash offered mattered, the researchers say. The group that was eligible for the lower reward value had the same infection rate as the control group that received no payments. While the impact of the cash incentives did not differ between males and females, the impact was larger among people with lower incomes.

“These are very encouraging results,” says Damien de Walque, a senior economist at the World Bank. “This was a proof-of-concept study that we now think should be replicated on a larger scale before concluding that this is an effective and feasible prevention approach.”