Virus bias? Transfusion infections under the radar

Virus bias? Transfusion infections under the radar

Two deadly infections spur new emphasis

Potentially fatal bacterial infections following platelet transfusions are flying below the infection control radar. The Centers for Disease Control and Prevention (CDC) recently drew attention to the problem by reporting two fatal infections following transfusions and noting that infectious disease physicians have a surprising lack of awareness about the problem.¹

Like allografts and tissue transplants, transfusion infections are somewhat of a gray area in the traditional parameters of infection control. While viral transfusion infections have drawn notice, bacterial infections have been quietly cooking on the back burner.

"Some infection control departments are more active than others in how they track adverse events related to transfusion and transplants," explains Mathew J. Kuehnert, MD, associate director of blood at the CDC national center for infectious diseases. "In other hospitals, the blood bank is more active in tracking them. But certainly I would consider it to be a procedure-associated infection that needs to be tracked and followed up on."

Yet only 36% of infectious disease physicians surveyed by the CDC and the Infectious Disease Society of America (IDSA) were aware that bacterial contamination is one of the most common infectious risks from transfusion.

"Most of the physicians were unfamiliar with the risks of bacterial infection transmitted through transfusion," Kuehnert says. "The survey didn’t get into why they were not aware, but certainly one possibility is that there is an assumption that blood, and for that matter other biologic products like organs and tissue, are sterile. That is an education gap. I think a lot of times when a patient has a transfusion reaction, the assumption is that it is caused by an allergic response unrelated to infection."

Heard of new AABB guidelines?

In addition, only 20% of the responding infectious disease physicians were familiar with the new American Association of Blood Banks (AABB) recommendations for bacterial testing of platelets. The AABB adopted a new standard on March 1, 2004, that requires member blood banks and transfusion services to implement measures to detect and limit bacterial contamination in all platelet components. Clinicians should collaborate with hospital transfusion services and blood collection center personnel to manage suspected infections in blood donors and patients (blood component recipients), the AABB recommends.

Protocols should be in place to help clinicians recognize and manage transfusion reactions, including those potentially caused by bacterial contamination. If bacterial contamination of a component is suspected, the transfusion should be stopped immediately, the unit should be saved for further testing, and blood cultures should be obtained from the patient. Bacterial isolates from cultures of the recipient and the unit should be saved for further investigation. Post-transfusion notification of appropriate clinical personnel is needed if cultures performed by the blood center or transfusion service identify slow-growing bacteria after the associated product has been released from inventory or transfused, the AABB recommends.

Unfortunately, the CDC/IDSA survey showed little awareness of the AABB guidelines and a general underappreciation of the risk of transfusion-related bacterial infections. "I think there is an assumption that blood products don’t contain bacteria," Kuehnert says. "These products come in a sealed container. I think we need to educate physicians about the ways these [platelet] products can be contaminated with bacteria. There are a number of ways the donor can have bacteria in the bloodstream without symptoms. It can be on the patient’s skin. Also, it could be contaminated during processing."

To assess clinician experience with transfusion-associated bacterial infections and knowledge of the new AABB standard, the IDSA conducted a survey of all 870 infectious-disease consultant members of the Emerging Infections Network. Completed surveys were received from 399 (46%) of the 870 members. Forty-eight (12%) respondents recalled consulting on 85 reactions to blood transfusions (i.e., of all types) potentially caused by bacterial contamination; 10 reactions were fatal. In 26 (31%) cases, contamination was confirmed by positive cultures of the recipient’s blood and transfused unit. The most common pathogens recovered were Staphylococcus andSerratia spp. A total of 143 (36%) respondents reported they were aware that bacterial contamination of platelets is one of the most common infectious risks of transfusion therapy. Seventy-eight (20%) indicated they had been familiar with the new AABB standard for bacterial detection in platelets before the survey; 359 (90%) said health care providers need to be aware of the standard.

Focus on viral infections

Part of the problem is that there has been such a focus on viral infections with blood products that bacterial risks have been given short shrift. "This is a problem that has been going on since blood transfusions were first done," Kuehnert explains. "A lot of the focus has been on infections that are viral — HIV, hepatitis. The concern was overwhelmingly toward screening for viruses, but now that the risk of viral infection has gone down so dramatically with the advent of these [viral] tests, what remains is the risk of bacterial infections."

Indeed, transfusion-associated bacterial sepsis is the second most frequently reported cause of transfusion-related fatalities in the United States, accounting for 46 (17%) of 277 reported transfusion deaths during 1990-1998, the CDC reports. Contaminated platelets are estimated to cause life-threatening sepsis in one in 100,000 recipients and immediate fatal outcome in one in 500,000 recipients. Each year, approximately 9 million platelet-unit concentrates are transfused in the United States; an estimated one in 1,000-3,000 platelet units are contaminated with bacteria, resulting in transfusion-associated sepsis in many recipients, the CDC notes.

To reduce this risk, clinicians should be aware of the new AABB standard and the need for bacterial testing of platelets to improve transfusion safety. In particular, "pooled platelets" are problematic because they are difficult to culture in a timely manner.

"Because of the requirements for them to be pooled hours before they are used, there really isn’t an easy way to culture them," Kuehnert says. "So to comply with the AABB standard, hospital blood banks are using nonculture-based methods like glucose sticks. It’s clear that these methods are not as sensitive as the culture-based methods. So there is a difference in the way these things are cultured, but no method is completely sensitive and fail-safe. As the two [fatal] cases illustrate, there are going to be situations where the culture methods didn’t detect every single contaminant in the unit."

Diagnosis needed due to false-negatives

Indeed, clinicians should be able to diagnose transfusion-associated infections, because even when testing complies with the new standard, false-negatives can occur and fatal bacterial sepsis can result, the CDC notes.

"Hopefully, this is going to be less of a problem now that the blood is screened for bacteria," he explains. "Even before this was implemented, we routinely got calls from physicians who suspected bacterial contamination after transfusion but didn’t know what to do as far as working it up. They needed help in determining [the protocol]."

Another problem is that even if testing on platelets is performed, blood banks may release units before the culture results are finalized, he notes. "That’s because in the vast majority of situations, if it hasn’t grown out in a couple of days, it is probably not going to grow out; but there are exceptions to that, and there are situations where the organism might grow out even after the unit has been transfused. So clinicians need to know that it is possible that they could get a phone call from a blood center or bank telling them that there was a unit that was transfused into their patients which is culture-positive [for bacteria]. Obviously, if they don’t know that the units are cultured at all, this could be a very confusing phone call."

Heightened awareness of the problem could help individual donors who present as patients to physicians. "Now that these units are being cultured, there are some situations where blood banks are going to be notifying the donors to say that, We cultured this out from your donation; you should consult with your doctor,’" Kuehnert adds. "So we want physicians to be aware that this screening is taking place and that there are certain organisms that they would probably want to follow up on for the health of the donor."

Reference

1. Centers for Disease control and Prevention. Fatal bacterial infections associated with platelet transfusion — United States, 2004 MMWR 2005; 54(07):168-170.