Resource Newsletter Archive
Tissue Safety: CDC Recommendations and Longstanding Tissue Services Policies
The CDC has been conducting an ongoing investigation into reports of septic arthritis, other post-surgical infections, and the Minnesota fatality last November following allograft transplants. The initial results were published in Morbidity and Mortality Weekly in December and March2. The March report, reprinted in The Journal of the American Medical Association3, ended with a series of recommendations to tissue processors to prevent disease transmission. At issue are several practices.
CDC recommended that tissue should be cultured for pathogenic microorganisms at procurement and that the time limit for tissue recovery after asystole should fall within AATB guidelines.
Tissue Services policies and procedures require that tissue be cultured at procurement, before it is exposed to antibiotics at processing. Tissue testing positive for any pathogenic contaminant must be discarded. These organisms include Clostridium, E. coli and other bowel flora.
“We want to get a complete picture of each tissue before it is exposed to antibiotics, because we don't want to kill or inhibit the growth of an organism before we have the chance to detect it,” explains Moogk. “Because our donor screening and procurement procedures are so strict, very few of our tissues test initially positive for pathogenic organisms, but we don't want to miss one if it's there.” (See the Spring 2002 issue of Resource for a complete explanation of Tissue Services microbiological procedures.)
In addition, Tissue Services microbiology policies are established in conjunction with independent specialists. “We have a level of confidence based on a long history of continually examining our microbiological testing policies with consulting laboratory medicine experts at the University of Washington,” explains Dawn Johnson, who is responsible for Tissue Services Quality Assurance.
Antibiotics aren't foolproof
The importance of testing at procurement cannot be overestimated, because an antibiotic wash at processing does not necessarily kill all pathogenic organisms, particularly anaerobic spore-forming organisms like Clostridium. According to the CDC's report, “Aseptic processing does not eradicate contamination with organisms, and antibiotic/antifungal solutions will not eliminate spores of organisms such as Clostridium spp.”
Organisms may escape detection through bacteriostasis, only to flourish when placed deep within a joint. As the Minnesota case demonstrates, such an infection may be severe enough to cause death.
“You can't become too reliant on test results alone to confirm safety,” says Moogk. “Microbiological culturing is just one aspect of our larger responsibility. The recent reports raise concerns about tissue processors whose background is in medical devices and pharmaceuticals, and whose understanding of the risks inherent in human tissue may not be adequate. They may have less respect for the potential for disease transmission and a misplaced confidence in sterilization protocols.”
Time limits are vital
The final CDC recommendation dealt with acceptable time limits after asystole for tissue recovery. It advises that recovery should be completed within 15 hours unless the donor is placed in a cooled environment within 12 hours of death, which is also the AATB standard. If the donor has been cooled, recovery must take place within 24 hours.
The Tissue Services's timing targets are even stricter; recovery is almost always completed within 12 hours of death unless the donor is cooled. If the donor has been placed in a cooled environment within six hours of death, procurement must occur within 24 hours. Tissue Services recoveries do not exceed AATB time limits.
When sterilization isn't enough
Finally, the CDC report briefly discussed sterilization methods other than antibiotics, chiefly irradiation, recognizing that it compromises tissue viability and therefore isn't an acceptable option for treating osteochondral and cardiovascular allografts. Also, the CDC observed that irradiation may not be 100 percent effective: it found that among the 26 recipients who developed post-surgical septic arthritis, “three patients received allografts that were reported to have undergone gamma irradiation.”
The Tissue Services uses low-dose irradiation only in cases where tissue tests positive for normal non-pathogenic skin flora or other environmental bacteria that are susceptible to radiation. More than 95 percent of all tissue is released as aseptically-processed without irradiation.
“Focusing on sterilization and decontamination alone to prevent disease transmission is not enough,” says Johnson. “It's critical to begin by minimizing the risk of infection transmission with procedures that both screen out donors who may carry infection and control all processes to prevent its introduction. We also have to identify any contaminant. The only way we can know for sure that an unacceptable organism will not be transmitted is to discard the tissue.”
(Editor's note: Photos accompanying this article were taken at Harborview Medical Center's Microbiology Laboratory, which supports Northwest Tissue Services programs. Above is clinical technologist Sue Gavin; at left is technician Alma Allen.)