(CNN) - Sex workers across 33 countries who face repressive policing -- identified as arrest, imprisonment, confiscation of needles, syringes, condoms, displacement to new area or physical or sexual violence by officers -- have a three times higher chance of experiencing physical or sexual violence, according to a new study.
They were twice as likely to have HIV and other sexual transmitted diseases than sex workers who were not exposed to repressive police violence and abuse of power. The group facing repressive policing was also more likely to have poorer mental health, reports the study, published Tuesday in the journal PLOS Medicine.
Lucy Platt, the lead researcher and an associate professor in public health epidemiology at the London School of Hygiene & Tropical Medicine, said that "repressive police practices increase harms" for sex workers. The paper also states that policy reform is needed to improve sex workers' safety.
Peter Greenhouse, spokesman and sexual health consultant for the British Association for Sexual Health and HIV, agreed. "This new comprehensive research definitively proves what we've known for many years," Greenhouse, who was not involved in the study, wrote in an email. "That repressive policing against sex workers increases violence against women and reduces access to sexual health care."
Sex workers, on average, are 13 times more at risk of HIV than the general population, according to the UK-based charity Avert, which provides HIV education. This is because they are economically vulnerable, are unable to negotiate condom use every time, and experience violence, criminalization and marginalization, Avert says.
The study looked at peer-reviewed research papers between 1990 and 2018 on sex work, legislation, policing and health. Data from 33 countries, including the UK, was used to estimate the average effects of repressive policing, compared with the effects that sex workers experienced in the absence of this.
Sex workers who were not exposed to repressive policing were 30% less likely to have condom-less sex than peers in repressive environments. The risk of HIV and other sexually transmitted diseases doubled and the risk of experiencing physical or sexual violence tripled in sex workers in repressive environments.
British campaign collective SWARM, which advocates for the rights of sex workers, connected CNN with one of its members, a sex worker who asked to be referred to by the pseudonym Katy Caradonna. "It is obvious to sex workers that when we have fewer rights at work -- and any criminalization of sex work reduces our rights at work -- we are less able to protect ourselves from violence or to seek redress, and predators know we are easier targets," she wrote in an email.
In its analysis, the study found many forms of police violence and abuses of power, such as arbitrary arrest, extortion, physical and sexual violence and failure to provide access to justice.
Fear of or actual arrest led to sex workers rushing negotiations with clients or working in isolated places that increase dangers, the study explained.
Reporting crimes is also an issue. "Police frequently failed to act on sex workers' reports of such crimes, or blamed and arrested sex workers themselves, meaning that offenders could operate with impunity and sex workers were reluctant to report to the police in [the] future," Platt said.
The study also identified that inequalities within the sex worker community were exacerbated by repressive policing, because police often target specific populations or settings, such as sex workers on the street or trans workers. This "further marginalized these vulnerable groups," Platt explained.
Similarly, police crackdowns on sex work venues restrict access to health services, making it difficult for outreach programs to find sex workers.
Previous research showed that decriminalization in New Zealand resulted in sex workers being better able to refuse clients and insist on condom use. Another study showed that decriminalization has the potential to reduce discrimination as well as denials of justice, denigration and verbal abuse.
The researchers hope that there will be changes to sex work laws. In the meantime, they advocate for the need to scale up funding of specialist sex and sex worker-led services to address the diverse health care and welfare needs of people selling sex.
One of the researchers, Pippa Grenfell, assistant professor of public health sociology at the London School of Hygiene & Tropical Medicine, added that "changes to sex work laws alone is not enough." She explained that there is a need for wider political action to tackle stigma and discrimination of sex workers by also addressing inequalities in other policies, like housing or social welfare.
There are some limitations to the study. Only a small number of papers that focused on decriminalization of sex work and the criminalization of purchase of sex were included. Similarly, few studies included data on trans female and cis-male sex workers.
Catherine Murphy, senior gender adviser at Amnesty International who was not involved in the study, noted in an email that "Criminalisation harms sex workers and this study shows that we have nearly three decades of research confirming this."
Deborah Gold, chief executive of the UK's National AIDS Trust who was not involved in the study, said in an email that the review presents "compelling evidence that supports the case that sex workers have been making on HIV for a generation: that repressive criminal law on sex work increases HIV risk and a host of other inequalities. This has to end."
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