Partner's behavior predicts STD risk better than individual behavior

April 2, 2009

GAINESVILLE, Fla. — Risky behaviors such as not using condoms or having sex with multiple people put young adults at risk for contracting sexually transmitted diseases, but perhaps not as much as the characteristics of their sexual partners, University of Florida researchers say.

The findings, which UF and University of Pittsburgh researchers report in the April issue of Sexually Transmitted Diseases, could help health-care providers better screen patients for STD risks, said Stephanie A. S. Staras, a UF assistant professor of epidemiology and health policy research in the UF College of Medicine.

“If you are choosing high-risk partners, you are much more likely to have an STD, even when we account for your condom-use patterns,” said Staras, the lead author of the study. “The theory is simple: You need to have sex with someone who has an STD to get an STD. Based on the prevalence of STDs in the United States, it seems like the public may not fully understand their risk.”

The study examined the sexual activities, partner characteristics and STD diagnoses of 412 subjects between the ages of 15 and 24. Among the subjects whose partners were categorized as high-risk, half were diagnosed with an STD. By comparison, about 40 percent of the young adults whose own behaviors were labeled as high-risk were diagnosed with an STD.

According to the Centers for Disease Control and Prevention, about 19 million people in the United States contract STDs each year. About half of them are between the ages of 15 and 24.

Health-care providers often ask patients about their own sexual behaviors, but inquiring only about a person’s own behaviors may cause some patients to slip through the cracks, Staras said. For example, some subjects in the study reported very low-risk behaviors but were having sex with very high-risk partners.

Adding a few simple questions about partner characteristics during STD screenings could help providers catch more patients who need to be tested and educated about condom use and other protective measures, Staras said.

“Partner selection is an area of STD prevention that could complement what we are already doing with promoting condom use, and could possibly really help people,” Staras said. “If somehow we could convince individuals to incorporate this information in a meaningful way into their decision-making, then we could reduce STDs.”

UF researchers measured five specific characteristics to gauge how risky certain partners were. These characteristics included whether the partner has a problem with marijuana or alcohol, was at least five years older or younger, had been in jail, had sex with other people in the past year or had an STD in the past year.

The researchers then created a composite, totaling up the number of negative partner characteristics for each subject and comparing them against the number of each person’s own individual risky behaviors, which ranged from how often they used condoms to how many people they had sex with.

Overall, researchers found considering all of the partner characteristics together was the strongest predictor for STDs. Young adults whose partners had five or more risk characteristics were three times more likely to have an STD than those whose partners had no more than two characteristics.

Of these characteristics, the most telling were if a partner already had an STD and if a couple had an age difference of more than five years. Subjects whose partners were five years older or younger than them were more than twice as likely to be diagnosed with an STD than those whose partners were around the same age, the researchers found.

“It’s all about the risk of the partner and sometimes we forget that,” said Richard A. Crosby, the DDI endowed professor and chairman of the department of health behavior at the University of Kentucky and a co-director of the Rural Center for AIDS/STD Prevention.

But Crosby, who was not involved in the UF study, said it’s also important for people to remember that the risks mentioned in the study are just generalizations, not set-in-stone giveaways for STDs.

“From a public health perspective, it’s important to understand these findings,” he said. “From a practical and prevention perspective, we still need to rely on people using valid methods of protection to avoid being infected or infecting.”