A new study finds people with a potentially fatal infection are more likely to be using prescription opioids than those without the infection. Studies in animals have found opioids suppress the immune system, The New York Times reports.

The study found people with invasive pneumococcal disease were 62 percent more likely than those without the disease to be using prescription opioids. The risk was highest for people taking high-potency opioids such as oxycodone, and long-acting opioids such as methadone and fentanyl patches.

The findings are published in the Annals of Internal Medicine.

“We can’t say that there’s proof of a causal link here,” said lead author Andrew D. Wiese of Vanderbilt University. “But providers should consider these findings when deciding whether to prescribe opioids, and in choosing what formulation to use. That’s true for anyone, but especially for those we know are already at high risk for infection, like older adults.”