Guidance

Chapter 10: microbiological testing of donation prior to transplantation

Updated 21 May 2024

Organs

Donor organs are removed under the sterile conditions of a surgical operation and transported cooled and bathed in fluid. Contamination of the organ and/or the preservation fluid with a pathogen may occur at any point of the organ retrieval and transplant process. Standard operating procedures (SOPs) must exist to minimise the potential for contamination of organs and preservation fluids. Appropriate processes allowing for the monitoring and review of these standard operating procedures must be in place.

If there is particular concern for the contamination of organ and or preservation fluid - for example, if the donor was known to have had a bacteraemia, or enteric injury has occurred during the retrieval procedure - then culture of the preservation fluid surrounding the organs should be undertaken. A positive culture will inform recipient management and clinically significant results, as assessed by the recipient centre infection specialists, must be communicated to NHS Blood and Transplant (NHSBT) Organ Donation and Transplantation (ODT) to ensure this information is conveyed to clinicians involved in the care of recipients of other organs and tissue from the same donor.

Tissues

Tissues must be procured in a suitable and appropriately risk-assessed facility, which must be either a Human Tissue Authority (HTA) licensed premises or operate under the authority of a licensed establishment under a third-party agreement. The licensed establishment must have written agreements with the staff or clinical teams responsible for tissue and cell procurement, unless they are employed by the same establishment. Where procurement premises are not specified ‘a priori’ as part of an existing licence or third-party premises, tissue retrieval may occur following a documented risk assessment in respect of contamination and health and safety risks carried out by the procurer prior to each procurement episode. This risk assessment can be undertaken and documented with the help of a proforma authorised by the ‘designated individual’.

Tissues should be retrieved as soon after death as possible, and within 12 hours if the body is not refrigerated. If the body has been refrigerated within 6 hours of death, retrieval of tissue must be completed within 48 hours of death. The exception is eye retrieval which must be undertaken within 24 hours of death, because of the need to preserve viability of corneal cells.

Tissues should be recovered using local sterile fields to minimise cross-contamination with microbes from other body sites. Where possible, sterile single- use instruments and equipment should be used with a minimal number of appropriately gowned and masked retrieval staff in attendance. Where re-usable instruments are used, these should be cleaned, sterilised and fully traceable to allow a record of which specific instruments were used on any given donor.

Retrieval should preferably precede any post-mortem examination of the donor and no other activities (embalming, autopsy or other tissue donor recovery) should occur at the same time in the facility. However, on occasion, and subject to an appropriate risk assessment, tissues outside the abdominal cavity (for example, heart, eyes and skin) may be retrieved at, or after, post-mortem examination.

Tissues should be processed and screened for microbial contamination by validated methods, the mandatory requirements of which are outlined in the HTA Guide to the Quality and Safety Assurance for Tissues and Cells for Patient Treatment.

Representative pre-processing samples (for example, bone or bone chips, pieces of tissue or swabs of tissues) should be transferred aseptically into appropriate culture media at the time of processing. Pre-processing microbiological testing is not required for eye donation.

Controlled work areas in tissue processing facilities should be monitored by air, settle plate, contact plate and glove print sampling to ensure that bacterial counts fall within the defined air quality grade for the type of process being undertaken.

Samples of the tissue must be taken before and after the tissue is exposed to decontamination agents. Enrichment cultures should be used to maximise the recovery of aerobic and anaerobic bacteria and fungi.

Tissues which cannot be terminally sterilised must be discarded if post-decontamination culture tests are positive. An exception is cryopreserved skin allografts which can be transplanted if only non-pathogenic bacteria in low numbers are present.

If an individual tissue fails bacteriological testing and is therefore required to be discarded, a risk-benefit analysis must be undertaken to determine whether other tissues from the same donor must also be discarded because of the risk of contamination.

The acceptance criteria for specified tissues, and the identification of organisms which are also considered acceptable at the various stages of processing, should be documented in written policies through consultation with a designated microbiologist. Advice should be sought for tissues that give equivocal or inconsistent bacteriological test results.

Bioburden estimations of marrow-depleted bone are not considered to be of value as the process of removing marrow effectively reduces microbial load. Similarly, estimation of bioburden of skin and amnion is not recommended as the former carries a substantial bioburden and the latter is surgically recovered under aseptic conditions. However, a heavy growth of bacteria from pre-process samples may signify gross contamination and the tissue should not be released unless able to be terminally sterilised by gamma irradiation or other techniques. The potential damage to the integrity of the tissue by the high numbers of bacteria should also be considered before it is used for transplantation.

To preserve cell viability, a number of tissues, including cryopreserved cardiovascular allografts, menisci or osteochondral grafts, cannot be irradiated. These may be decontaminated with mixtures of antimicrobials. The antimicrobial solutions used should be validated to be effective against the range of bacterial species normally recovered from such tissues and the tissue bank should develop a list of species exclusion criteria based on an assessment of the clinical risk of serious infection in the recipient. Cardiovascular tissues must also be tested for Mycobacterium species, and fungal contamination using validated techniques. Where corneas are stored by organ culture, samples of the medium should be tested during storage for bacterial and fungal contamination. If contamination is detected, the tissue should be discarded. The opportunity for detecting contamination of corneas stored by hypothermia is limited and typically testing is not undertaken.

Gametes and embryos

Appropriate skin cleansing procedures must be carried out prior to the provision of semen samples, surgically retrieved sperm and eggs but sterility cannot be guaranteed for gametes.

In vitro fertilisation and embryo culture carries a risk of microbiological contamination. Laboratory procedures must include procedures to minimise this risk and subsequent loss of embryos. This includes consideration of both endogenous and exogenous contamination. Embryos found to be growing in contaminated medium should not be transferred.

Full quality assurance procedures should be in place.

Human Fertilisation and Embryology Authority (HFEA) guidance is provided in the HFEA code of practice.

See a list of all chapters in this guidance