A study from Emory University has suggested that states with constitutional marriage bans are more likely to have higher rates of HIV infection.

The research, titled Tolerance and HIV, used economic theories to calculate how policies and attitudes could impact on HIV diagnoses.

It was found that states with a constitutional ban on same-sex marriage had four more cases per 100,000 people. It was calculated that a rise in tolerance in the 1970s and 1980s led to a decrease in one case of HIV for every 100,000 people.

The study used data from the General Social Survey, which has tracked the attitudes of Americans during the past four decades.

Researchers suggested that less tolerance meant people were more likely to engage in risky behaviour such as cottaging, thus increasing rates of transmission.

“Intolerance is deadly,” said Hugo Mialon, an assistant professor of economics at Emory University.

“Bans on gay marriage codify intolerance, causing more gay people to shift to underground sexual behaviors that carry more risk.”