As abuse of injected heroin and other addictive opioids spreads throughout the United States, heart experts warn of a growing threat: strokes caused by infections contracted through dirty needles.

Injecting heroin or other opioids can enable bacteria to get into the body. These germs then infect and inflame heart valves, creating a dangerous condition called infective endocarditis.

Looking at U.S. data on hospitalizations between 1993 and 2015, the researchers identified nearly 5,300 patients hospitalized with stroke from opioid-related infective endocarditis. These cases have risen steadily: from 2.4 per 10 million people in 1993 to 18.8 per 10 million people in 2015, the findings showed.

Once infective endocarditis occurs, clumps of infected tissue can break off and travel to the brain’s blood vessels and block them, triggering a stroke.

These types of stroke have become more common in recent years, with the largest increase being among white people in the northeastern and southern U.S