THE Centers for Disease Control and Prevention warned open-heart surgery patients recently that they were at risk of a deadly infection linked to a medical device used during their operations. Now, worried consumers say they are having a hard time getting information from hospitals and doctors about what they should do.

More than a half-million patients could have been exposed to bacteria that can cause serious illness or death. That's the estimated number of patients who had open-chest surgery involving potentially contaminated equipment in the past several years. The bacteria are a type of nontuberculous mycobacteria, or NTM. Although infections are rare, experts are worried because patients may not develop symptoms or signs of infection for months, so diagnosis may be missed or delayed.

The device is a heater-cooler unit, which helps keep a patient's circulating blood at a specific temperature during operations. It's used in an estimated 250,000 surgeries in the United States every year, including cardiac bypass, valve replacement and liver transplants. About 60 percent of these procedures use the German-made model that has been linked to the infections, the Stöckert 3T heater-cooler, made by LivaNova PLC, formerly Sorin Group Deutschland GmbH.

The CDC is advising hospitals to notify patients who had open-chest surgery involving these devices going back to Jan 1, 2012. There is new information that indicates these devices were probably contaminated during manufacturing.

The Washington Post's Lena H. Sun spoke with consumer advocates and health experts, including CDC's Mike Bell, deputy director of health-care quality promotion, about what patients should do.

Q: How do I know if I need to be worried?

A: If you're not having symptoms, there's nothing you need to do. But patients who have had open-heart surgery should seek medical care if they're having nonspecific symptoms associated with infections, such as night sweats, muscle aches or pain, weight loss, fatigue or unexplained fever.

Q: What if I don't have symptoms but want to make sure my doctors know about this situation?

A: The CDC has a sample letter that patients can download, customize and take to their cardiologist or family doctor or whomever you see for ongoing medical care. The letter explains the risk of infection and CDC's recommendation that clinicians consider NTM as a potential cause of unexplained chronic illness.

"Patients should say to their doctors, 'I want you to put this in my file and be aware this could happen. If I start having infection symptoms, I want to be tested,' " said Lisa McGiffert, director of Consumers Union's Safe Patient Project.

Q: What if my open-chest surgery took place before Jan 1, 2012?

A: The CDC's Bell said the vast majority of infections flare up within four years of exposure. But regardless of when you had this type of surgery, if you are having symptoms, you should contact your health-care provider as soon as possible.

Q: Are there any drugs I can take to prevent these infections?

A: Currently, there aren't any safe prophylactic treatments.

Q: Are these infections treatable?

A: Yes. A specific combination of antibiotics can treat NTM infections.

Q: Why is the CDC worried about these devices?

A: Researchers have found that fans on these units may blow bacteria from inside the machine into the operating room. If the bacteria land on a heart valve that is about to be implanted or a surgical wound, it could cause an infection.

Q: How many hospitals do this kind of operation in the United States?

A: An estimated 1,200 hospitals in the United States perform bypass operations, according to federal government sources.

Q: What if my hospital used a different brand of heater-cooler?

A: These machines operate in similar ways. They could be contaminated in similar ways and also pose infection risk.

Q: What is the risk of infection?

A: In hospitals where at least one infection has been identified and linked to the device in question, the risk was low, between 1 in 100 and 1 in 1,000. CDC officials say patients who had valves or other prosthetic implants are at higher risk.

Q: How long does it usually take for these infections to show up?

A: It may take months and up to several years after the operation. Virtually all the cases reported so far in Europe and the United States have occurred within four years of surgery.

Q: What are these bacteria? Can an infected person spread it to others?

A: NTM is common in water and soil. The bacteria rarely make healthy people sick. The danger arises when these bacteria enter the chest cavity or an open wound, especially in someone with a weakened immune system. The bacteria cannot be spread to others.

Q: How many illnesses and deaths have been linked to these infections?

A: Between January 2010 and August 2016, the FDA received 91 reports from around the world about these devices. At least 79 were patient infections, with 55 in the United States. The infections include at least 12 deaths, including seven U.S. deaths. (In some cases, a report may describe a cluster of patients. In other cases, more than one report may be submitted from the same incident.)

Hospitals in Iowa, Michigan and Pennsylvania have reported infections.

Q: Is there a test to know whether I've been exposed?

A: There is no such test. Infections can only be diagnosed by growing the bacteria in a lab. But that may take up to two months or longer. What's more, getting the right kind of specimen depends on where the infection is. It could be in the blood, or it might show up in an infected wound.

"It has to be cultured under the right circumstance so the finicky bacteria will actually grow," Bell said.

Q: Why hasn't my hospital notified me? There's nothing on the website, and I can't reach a person who knows anything.

A: Many patients say they're frustrated by their inability to find out anything from the hospital where the operation took place. The hospitals have been getting alerts for the past year from the CDC and the Food and Drug Administration. But the CDC and FDA don't have authority to require hospitals to notify patients. The American Hospital Association, an industry association, says it has advised its members to review and determine how best to follow the CDC recommendations. But Jay Bhatt, the AHA's chief medical officer, said it takes time to review records and identify patients who might have been affected.

Q: How many of these Stöckert 3T heater-cooler devices are there? Why haven't these devices been recalled?

A: As of July 2015, the company publicly reported there were 1,914 devices in health-care facilities around the world, including in the United States. In 2015, the company recalled the instructions for use, but not the device itself. The FDA imposed an import alert in December 2015. The devices are critical for lifesaving surgery, and a recall could result in many patients being harmed.

Q: I'm supposed to have elective surgery to have a heart valve replaced. Should I postpone the surgery?

A: For nonemergency surgeries, patients might want to ask their doctors if they have the option of waiting for a little while, says CDC's Bell. Patients should make sure their surgeons and hospitals disclose these risks, in writing, during the pre-surgery informed-consent discussions.

Q: What are hospitals doing in the meantime?

A: Hospitals are working through the logistics involved in notifying patients.

"Facilities are not well set up to receive a large number of public calls," said Bell. He said hospitals in Pennsylvania and Iowa that had clusters of infections had to set up a special telephone number to receive inquiries and guide people to the next step.

Hospital officials are also looking to find ways to minimize the risk of infection, such as keeping the devices outside the operating room, or looking for alternative machines that don't have fans, Bell said.

"Every hospital is thinking about how to make this problem no longer exist," he said.