NBC San Diego reports on the study findings.

Teenage sex workers in two cities on the border between Mexico and the United States are three times more likely to contract HIV than adult sex workers in those cities, according to a study published in the Journal of the American Medical Association and reported by NBC San Diego.

The study included 603 female sex workers 18 years old and younger in the cities Tijuana and Ciudad Juarez. It was conducted by the University of California, San Diego, School of Medicine. In addition to answering questions for the study, participants also gave blood samples for HIV testing.

Researchers found that 6 percent of those who started sex work as teenagers were HIV positive, compared with slightly less than 2 percent among those who started sex work as adults.

Those who began sex work at a younger age were also more likely to be violently coerced into the sex. They also had more clients than the older workers, and they were seven times less likely to use a condom during their first month in the sex business. The researchers added that injection drug use also contributed to higher HIV rates among younger sex workers.

“Our study highlights the importance of social and structural factors, especially high levels of violence encountered by adolescents in the sex trade, in understanding vulnerability to HIV,” senior author Kimberly Brouwer, PhD, of UC San Diego told NBC.