Need more proof that individual behavior isn’t the only thing that determines whether you acquire HIV? Talk to the 14,716 people who inject drugs included in a recent study by researchers at the Centers for Disease Control and Prevention (CDC), published in Morbidity and Mortality Weekly Report.

In 2018, 36% of white participants reported using a needle that someone else had already used—a major risk factor for acquiring HIV—more than twice the rate of Black people (16%) and about a third higher than Latino people (22%). When it came to sex, Black participants were less likely than whites to report having had condomless vaginal or anal sex.

Meanwhile, Black participants were slightly more likely than white people to report having been tested for HIV in the last year (59% versus 53%, respectively). In addition, they were more likely to report having participated in an HIV prevention program in the previous year (34% versus 29%, respectively).

Based on individual behavior, you’d think that white people who inject drugs would acquire HIV more often. But the opposite happened: More than 1 in 10 Black people who inject drugs (12%) acquired HIV, compared with 5% of white people and 7% of Latino people.

So what was different? CDC scientist Senad Handanagic, MD, and colleagues reported that just 40% of Black people received sterile syringes from a needle exchange, compared with 63% of both white and Latino participants. And Black participants were least likely to access medication-assisted treatment for opioid use disorders.

The bottom line: Everyone in the study engaged in activities that could expose them to HIV, but Black participants bore the brunt of transmission despite more conscientious behavior.