Epidemiology Unit

We collate and analyse data from the 4 UK blood services (NHS Blood and Transplant, Welsh Blood Service, Northern Ireland Blood Transfusion Service and the Scottish National Blood Transfusion Service) to produce surveillance reports and inform or evaluate policy changes relating to infection risk.

Our work helps to maintain a safe supply of blood, tissues and organs by:

• Informing donor selection criteria
• Monitoring trends in infections
• Following up any reported post-transfusion infections

Blood donors are a well characterised low risk group, with around 1.8 million donations screened in the UK each year for markers of HBV, HCV, HIV, HEV, syphilis, and HTLV in new donors.

The information we collect also contributes to our understanding of the epidemiology of blood borne infections, and there is potential for following up infected donors. This could provide additional information to public health specialists working to reduce infections in the general population, through prioritising population groups for interventions and delivery of care.

The unit manages the UK Blood Donor Surveys to help assess the impact of donor selection policy changes including FAIR. (See 'Documents relevant to the UK blood supply' for FAIR I, FAIR II and FAIR II on the Joint UK Blood Transfusion and Tissue Transplantation Services Professional Advisory Committee website)

We also manage the HTLV National Register in collaboration with UKHSA, NHS Blood and Transplant and Imperial College Healthcare NHS Trust. The register consists of donors with HTLV and HTLV specialist clinic attenders, to inform public health about onset and progression of HTLV associated disease.

The unit manages a series of national surveillance schemes. Data from these schemes is used to assess and improve blood, tissue and organ safety. These schemes include:

• Infections in blood donors: monitored through donation testing and the collection of information about identified infected donors.
• Infections in tissue donors (including stem cell and cord blood donors): 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 from the four UK blood services, as the national infection co-ordinator as 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.
• Transfusion Microbiology Epidemiology Review (TMER): looking for evidence of transmission of CJD via blood transfusion.

Over 27 years of surveillance, we have identified low numbers of transmissions due to a number of risk reduction strategies.

To reduce the risk of transfusion-transmitted viruses, parasites and prions, these include:

• Leucodepletion: introduced in 1999 to reduce prion risk
• Hepatitis C nucleic acid testing (NAT): added to routine screening in 1999, effectively preventing HCV transmissions to date
• HIV antigen testing: introduced in 2001
• HIV NAT: introduced in 2002
• HTLV antibody testing: began in 2002 and was later limited to first time donors and donors of donations manufactured into non-leucodepleted components such as granulocytes
• Hepatitis B NAT: introduced in 2009
• Hepatitis E NAT testing: added in 2016
• Hepatitis B core antibody testing: introduced in 2022 for additional safety

Between 1996 and 2023, several cases of HBV and HEV transmission were reported, resulting in additional tests being introduced for anti-HBc in 2022 and HEV RNA from 2016.

No HTLV nor HIV transmissions have been reported and confirmed since 2002, the last HCV transmission was reported in 1997.

Strategies to reduce the risk of transfusion-transmitted bacterial infections include:

• Bacterial screening of all platelets: introduced in Northern Ireland in 2000, Wales in 2002, Scotland in 2003 and England in 2011
• Diversion of the first 30ml of blood: implemented from 2002
• Arm cleansing using a Chloroprep wand: rolled out between 2006 and 2009

For more data on this topic, visit the Serious Hazards of Transfusion (SHOT) website:

Number of recipients with confirmed/probable Transfusion-Transmitted Infections (TTI) - SHOT