The NHSBT / PHE surveillance programme is a series of national schemes that monitors infection in blood, tissue and organ donors, and transfusion recipients.
NHSBT / PHE epidemiology unit
The joint NHSBT / PHE epidemiology unit collates and analyses information from testing centres, reference laboratories and clinicians of the UK blood services 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 risks of window period donation
- outcome of investigations into suspected post-transfusion infections
NHSBT / PHE surveillance programme
The NHSBT / PHE epidemiology unit surveillance programme is a series of national schemes that monitors infection in:
- blood, tissue and organ donors
- transfusion recipients
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)
- treponemal (like syphilis) infections
Donations are only released to the blood supply if none of these markers are detected.
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 JPAC donor selection guidelines (DSG).
Surveillance of infections among tissue donors
NHSBT tissue service operate 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 antibodies (such as syphilis infection)
Data have also been gathered on samples tested by the:
- Scottish National Blood Transfusion Service (SNBTS)
- Northern Ireland Blood Transfusion Service (NIBTS)
Surveillance of transfusion transmitted infection (TTI)
PHE operates a surveillance system to collect information about infections suspected to have been transmitted by transfusion. This forms part of serious hazards of transfusion (SHOT), the UK’s professionally-led haemovigilance 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 infectious. 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 / PHE 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
Risk estimates in the UK, 2011 to 2013
The estimated risk that a donation entering the blood supply is a potentially infectious window period donation: risks specific for HBV, HCV and HIV in the UK, 2011 to 2013.
Although current blood donation testing strategies minimise the risk of transfusion transmitted infections in the UK, on very rare occasions potentially infectious donations are not detected and may enter the blood supply.
Window period (WP)
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. Here, we calculate window period risk as the risk multiplied by 1 million. This is the number of potentially infectious donations in 1 million donations entering the blood supply with 95% confidence intervals (by simulation), and the number of millions of donations entering the blood supply before 1 of those donations can be expected to be a potentially infectious donation.
The estimated number of potentially infectious window period donations per million donations tested that entered the UK blood supply between 2011 and 2013 were:
- 0.46 for HBV
- 0.026 for HCV
- 0.17 for HIV
HIV risk was almost unchanged from the estimate for 2010 to 2012. The decrease in HBV risk is partly accounted for by a change in the estimated infectious window period from 38.5 to 30 days, the decrease in HCV risk is due to a decrease in incidence.
At current donation levels of approximately 2.3 million donations each year in the UK, it is estimated that testing will not identify approximately:
- one potentially infectious HBV window period donations every year
- one potentially infectious HCV window period donation every 16.7 years
- one potentially infectious HIV window period donation every 2.6 years
Donations given by new donors and entering the blood supply were estimated to be more likely to be infectious compared with donations from repeat donors.
Of the 3 viruses, HBV was estimated to be the virus most likely to be missed during 2011 to 2013 due to a window period donation.
Despite anti-HTLV testing of blood donations in the UK, the risk is not estimated. This is because of the:
- uncertainty about the presence and/or duration of an infectious window period for HTLV
- relevance of the calculation, given that widespread leucodepletion of all components is likely to significantly reduce onwards transmission to patients
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 2012’ document, part of ‘Safe supplies’, the NHSBT / PHE epidemiology unit’s annual review. 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 the reference laboratory 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 propionibacteria, 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