The Centers for Disease Control and Prevention on Thursday warned that contaminated medical devices used in open-heart surgeries could be to blame for a rash of infections in patients in the United States and Europe.

Data published in the CDC’s Morbidity and Mortality Weekly Report indicate that at least 11 patients in the US were infected with bacteria from a heater-cooler device that maintains patients’ internal temperatures during surgery. Previous reports indicated that six people in Switzerland were infected, and dozens of Americans have come forward with symptoms.

CDC issued an advisory for health care providers, and urged patients who have had open-heart surgery to seek medical care if they are experiencing symptoms associated with infections. The agency estimated that some 250,000 patients undergo surgeries using the device every year.

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Health officials cautioned that “while these infections can be severe, and some patients in this investigation have died, it is unclear whether the infection was a direct cause of death.”

“Available information suggests that patients who had valves or prosthetic products implanted are at higher risk of these infections,” the CDC said in a statement.

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The agency estimated that in hospitals where at least one infection has been identified, the risk of a patient getting an infection from the bacteria was between about 1 in 100 and 1 in 1,000.

The heater-cooler device associated with the infections is made by London-based LivaNova.

When heart valves become worn out, they stop working, and patients need open-heart surgery to have artificial valves put in so that the organ can continue to pump blood. But because it’s nearly impossible to operate on a still-beating heart, doctors insert tubes that will allow the blood to flow out of the body, and remain oxygenated.

One of those machines is the heater-cooler device, which does exactly what it sounds like: It keeps the blood at the right temperature. The water that helps maintain the temperature does not come into contact with the blood — but the bacteria has another way of moving into the patient.

“We established that the same mycobacteria go out of the water of the heater-cooler unit, because it’s not airtight,” said Dr. Hugo Sax, an infectious disease specialist at the University Hospital Zurich, in Switzerland. “They go into the air, they float around the operating room, and then they fall down on the artificial heart valve that is put outside of the patient before being inserted.”

Once inside the body, it begins to form a layer of slime, which allows it to grow slowly, undetected — sometimes for years, Sax explained.

“I’m worried because if you get the disease it’s really deadly, in the sense that we have seen half the patients die from it,” he said. “We are eager to have doctors know about this, because the symptoms are not very telling and not very specific.”

On Thursday, LivaNova responded to the advisory, saying the company was reaching out to users of their heater-cooler devices to let them know about the risks.

“We are working with regulators, clinicians, and all relevant parties to resolve this important industry-wide issue,” said the company in a statement.

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The CDC and the Food and Drug Administration initially raised concerns about the devices being contaminated in 2015. On Thursday, the CDC said it had recently completed laboratory tests and was releasing further information.

“It’s important for clinicians and their patients to be aware of this risk so that patients can be evaluated and treated quickly,” Dr. Michael Bell, deputy director of CDC’s Division of Healthcare Quality Promotion, said in the statement. “Hospitals should check to see which type of heater-coolers are in use, ensure that they’re maintained according to the latest manufacturer instructions, and alert affected patients and the clinicians who care for them.”

The CDC identified the bacteria infecting the devices as Mycobacterium chimaera, a species of nontuberculous mycobacterium often found in soil and water.

This story has been updated with a statement from LivaNova.