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Death rates from a rare heart infection have risen among young adults over the past two decades, a trend that may be driven by complications of substance use disorder, new research suggests.

The  showed death rates for infective endocarditis – which develops after bacteria enter the bloodstream and settle in the heart lining, heart valve or blood vessels of the heart – declined in most adults across the U.S. but rose among those 25 to 44. Findings were published Wednesday in the Journal of the 91ÊÓƵ.

"Our study findings raise a public health concern, especially since the deaths in younger age groups are on the rise," the study's lead author, Dr. Sudarshan Balla, said in a . Balla is an associate professor of medicine at the West Virginia University Heart and Vascular Institute at J.W. Ruby Memorial Hospital in Morgantown. "We speculate that this acceleration was likely, in the most part, due to the opioid crisis that has engulfed several states and involved principally younger adults."

People with previous heart valve surgeries, valve abnormalities, artificial valves, congenital heart defects or prior infections of the heart are at greater risk for infective endocarditis. But it also can be caused by complications from injecting illicit drugs.

Researchers analyzed death certificate data from the Centers for Disease Control and Prevention to identify state and national death trends related to the condition, with an eye toward differences in age, sex, race and geography from 1999 to 2020. Because the opioid epidemic emerged during this time frame, they also looked at data related to substance use.

The overall death rate associated with infective endocarditis, when adjusted for age, dropped from 26 per million people in 1999 to 22 per million in 2020, the analysis showed.

However, the analysis also showed an average annual increase in deaths of more than 5% for adults 25 to 34 years old and more than 2% for those 35 to 44. Among adults 45 to 54, death rates were stagnant, while rates for those 55 and older fell significantly.

Among adults 25 to 44, substance use disorder was associated with a rise in multiple causes of death. The rise in deaths due to infective endocarditis was particularly steep in Kentucky, Tennessee and West Virginia compared to other states, where death rates fell or remained stagnant.

"We found that substance use was listed as a contributing cause that could explain the higher death rates in the younger age groups and also in the states in those who died due to endocarditis," Balla said. "Comprehensive care plans for those treated for infective endocarditis should also include screening and treatment for substance use disorder."

A direct cause-and-effect relationship between substance use disorders and increasing deaths caused by infective endocarditis among younger adults could not be determined, researchers said, because of the limited medical details available and possible errors in death certificates.

Some states have begun public health programs to reduce the risk of infectious diseases and bacterial and fungal infections caused by intravenous drug use.

But "whether these programs make an impact is yet to be determined," Balla said.