Animal studies have shown that opioids suppress the immune system, but their clinical effect in human infections has not been widely studied.

In a new report published in The Annals of Internal Medicine, researchers looked at 1,233 patients with invasive pneumococcal disease, an infection that is fatal in about 10 percent of cases, with higher death rates in the elderly. They compared them with 24,399 controls.

People with invasive pneumococcal disease were 62 percent more likely than those in the control group to be using prescription opioids. The association was strongest for high-potency drugs like oxycodone and for long-acting drugs like methadone and transdermal fentanyl. The study controlled for many variables, such as sex, race, alcohol use and cardiovascular disease.

“We can’t say that there’s proof of a causal link here,” said the lead author, Andrew D. Wiese, a postdoctoral fellow at Vanderbilt University. “But providers should consider these findings when deciding whether to prescribe opioids, and in choosing what formulation to use.”

Two of the co-authors have received payments from drug companies.