The NHSBT and UKHSA surveillance programme is a series of national schemes that monitors infection in blood, tissue and organ donors, and transfusion recipients.
NHSBT and UKHSA epidemiology unit
The NHS Blood and Transplant (NHSBT) and the UK Health Security Agency (UKHSA) (formerly Public Health England) Epidemiology Unit comprises a small team of epidemiologists and public health specialists working with scientific and clinical colleagues across both NHSBT and UKHSA. The unit was established in 1995 to monitor infections in blood donors and transfusion recipients. Over time the role of the unit has expanded and we are now responsible for monitoring infections in blood, tissue and organ donors, and transfusion recipients. Data from the 4 UK blood services are collated and analysed by the unit to produce surveillance reports and inform/evaluate policy changes relating to infection risk.
Data from the 4 UK blood services are collated and analysed to provide data on the:
- number and rates of infections in donors
- number of donations which would otherwise have been lost if additional tests were not used
- estimated residual risk of a hepatitis B virus (HBV), hepatitis C virus (HCV) or human immunodeficiency virus (HIV) window period donation
- outcome of investigations into suspected post-transfusion infections
NHSBT and UKHSA surveillance programme
The NHSBT and UKHSA surveillance programme is a series of national schemes managed by the unit which include:
- infections in blood donors: monitored through the surveillance of donations tested and the collection of information about infected donors identified.
- infections in living surgical bone and deceased tissue donors (for NHSBT): monitored in a similar way to blood donors.
- infections in deceased organ donors: monitored in a similar way to blood donors.
- reported post-transfusion infections: monitoring investigations among transfusion recipients and forms part of Serious Hazards of Transfusion (SHOT).
- emerging infections: relevant reports from various sources are collated and reported on a monthly basis or as necessary, as a national horizon scanning scheme.
- The Transfusion Medicine Epidemiology Review in partnership with the National CJD Research and Surveillance Unit (NCJDRSU) Edinburgh, a study which aims to look for evidence of transfusion transmission of Creutzfeld-Jakob Disease (CJD).
The following UK and Irish blood services contribute data, which are used to assess and improve blood and tissue safety:
- NHS Blood and Transplant
- Scottish Blood Transfusion Service
- Welsh Blood Service
- Northern Ireland Blood Transfusion Service
- Irish Blood Transfusion Service
Surveillance of infections in blood donors
Every donation is tested for markers of:
- hepatitis B (HBV)
- hepatitis C (HCV)
- hepatitis E (HEV)
- treponemal infections (like syphilis)
Donations are only released to the blood supply if none of these markers are detected.
Donations from new donors and those used for non-leucodepleted components are tested for human T cell lymphotropic virus (HTLV).
Additional testing may be carried out depending on a donor’s relevant history, for example, malaria testing if the donor has recently travelled to a country where malaria is endemic. For further information, see the Joint UK Blood Transfusion and Tissue Transplantation Services Professional Advisory Committee (JPAC) donor selection guidelines (DSG).
Surveillance of infections among tissue donors
NHSBT tissue service operates a tissue donation and banking programme from living and deceased donors. Donations include:
- surgical bone (mainly femoral heads)
- heart valves from living and deceased donors
Additionally, NHSBT runs the NHS cord blood bank. All tissue donors (including cord blood donors) are routinely tested for markers of:
- HTLV infection
- treponemal infections (like syphilis)
Surveillance of transfusion transmitted infection (TTI)
UKHSA operates a surveillance system to collect information about infections suspected to have been transmitted by transfusion. This forms part of SHOT, the UK’s professionally-led hemovigilance scheme.
Any possible incident of infection due to transfusion should be reported by the hospital where the transfusion took place, to the local blood centre. Each case reported is fully investigated to identify the infection and to confirm, or refute, that the blood transfusion may have been the source of infection. After the investigations are closed, reported incidents are classified as a TTI according to the definition specified below.
Blood centres in Scotland report all incidents to the Scottish National Blood Transfusion Service, and the details and conclusion of each case are then provided to the NHSBT and UKHSA epidemiology unit.
A report of an infection suspected to be due to transfusion is classified as a TTI if the following criteria are met at the end of the investigation:
- the recipient had evidence of infection following transfusion of blood components and there was no evidence of infection prior to transfusion and no evidence of an alternative source of infection
- at least one component received by the infected recipient was donated by a donor who had evidence of the same transmissible infection
- at least one component received by the infected recipient was shown to contain the agent of infection
Viral residual risk estimates in the UK
The viral residual risk for UK blood donations is defined as the risk that a potentially infectious donation is not detected by routine blood donation screening and could potentially be available for transfusion. This is mostly because a blood donation is made during the potentially infectious ‘window period’ (WP) early in the course of infection, when the test in use will not detect the marker of infection.
Risk is usually described as the estimated residual risk per million donations tested, or up to the estimated number of years of blood donation screening before a potentially infectious donation is not detected. It is not the estimated risk of transmission, since transmission will also depend on the amount of undetected virus in the component which may vary by type of components transfused. Residual risk is only calculated for HBV, HCV and HIV.
Each year the unit calculate residual risk for the UK based on surveillance data for the previous 3 years.
View the latest residual risk estimates.
Bacterial screening of platelets
The transfusion of a platelet or red cell pack contaminated with bacteria may result in a TTI in the recipient. The frequency of confirmed bacterial TTIs is greater in platelet transfusions because these packs are stored at 22°C, which provides favourable conditions for bacterial growth.
A bacterial screening surveillance programme was also introduced to collect data on the number of positive results in England and north Wales over time, and by centre.
Bacterial screening is carried out using the BacT/ALERT system. More details on the method of screening is available in the ‘Data sources and methods’ documents for each year of ‘Safe supplies’, the NHSBT and UKHSA Epidemiology Unit’s annual report. All initially reactive samples are sent to the national bacteriology laboratory for testing, and further investigations of the donor may be carried out following receipt of these results.
A platelet donation may be made either by:
- apheresis, where one component donor can donate up to 3 platelet packs
- pooling platelets from whole blood donors, where 4 donors contribute to 1 pooled platelet pack
The most frequently isolated organisms were skin flora, which are:
- slow-growing organisms unlikely to result in a TTI in a recipient
- likely to have entered the platelet pack from the venepuncture site of the donor arm
These organisms can be isolated from:
- hair follicles
- deeper layers of the skin where skin cleansing agents will not penetrate
The Transfusion Medicine Epidemiology Review (TMER) is a collaborative project between the UK NCJDRSU and the UK Blood Services. The main purpose is to investigate whether there is any evidence that CJD or variant Creutzfeldt-Jakob disease (vCJD) may have been transmitted via the blood supply.
View more information on the TMER project.
The HTLV register is a nationwide cohort study for monitoring progression of HTLV infection over a number of years. Participants on the Register are made up of both positive and negative individuals. Surveys are collected every 2 years to determine whether HTLV infection is likely to progress in a way that limits everyday life experiences for those positive for the virus. The HTLV Register is a joint project between UKHSA and Imperial College London NHS Trust.
View more information at HTLV: national register.