Calls to tackle protein risk

Following the publication of research, which estimated that around one in 2,000 people in the UK may carry variant Creutzfeldt-Jakob Disease (vCJD) protein,1 the Science and Technology Committee recently presented evidence on vCJD and the ongoing risk it poses to the UK. Ordered by the House of Commons, the meeting took place on 27 November 2013 and heard evidence from a number of experts including Professor Collinge, director of the Medical Research Council (MRC) Prion Unit, UCL Institute of Neurology. He highlighted the fact that, in addition to the 20,000 or 30,000 people that are predicted to be infected and are carriers in the population at the moment, there are around 6,000 people in the UK who have been notified that they are at increased risk of developing the disease as a result of receiving either blood from a person who went on to develop vCJD or blood products that are implicated, or who have been exposed to contaminated surgical instruments.2 Andrew Miller MP, chair of the science and technology committee, said: “More than twenty years on from the BSE crisis, studies have suggested that thousands of people may still carry the infectious agent thought to cause vCJD – the human form of ‘mad cow disease’. “Although these people may never go on to develop symptoms of vCJD, important questions remain to be asked about the potential risk posed by this terrible condition and what the Government should be doing to reduce the spread of infection.”3

Protein removal: surgical instruments

Against a backdrop of heightened awareness, the issue of transmission risk through contaminated surgical instruments was high on the agenda at the Institute of Decontamination Sciences’ (IDSc) annual conference, as experts considered the problematic challenge of detecting and removing residual protein. Opening the discussion was a presentation on ‘limitations on residual protein contamination on instruments’, by Nigel Tomlinson, who previously advised the Department of Health (DH) on decontamination issues in his role as principal scientific adviser. (He has now retired.) He explained that residual protein is defined as ‘a mass of protein that remains on an instrument after it has been washed and disinfected, usually in a mechanised way, within a sterile service department’. This potentially poses a risk of protein based infection (such as vCJD), and can affect the acceptability of the instrument for surgical use. While working for the DH, Nigel Tomlinson received complaints about the functionality of some instruments: “There is a relationship between instrument design and levels of contamination, and the effectiveness of the washing process,” he pointed out. He acknowledged that the decontamination community would like to see a lower level of bio-molecular protein contamination of instruments at the end of the process and, in an effort to tackle the problem, the DH has adopted a riskbased strategy involving a number of key steps including the investigation of detection and quantification methods, the optimisation of washing and disinfection, and the development of new decontamination techniques. The first step has included the funding of research into improving protein detection and quantification. There have been a number of pilot studies established to investigate various approaches, with the aim of suppressing vCJD-related risks, within the hospital decontamination setting. The emphasis has been on examining these approaches in practice, rather than simply using a scientific team. “Practicality matters – a good idea has no value if it cannot be implemented,” Nigel Tomlinson pointed out. The pilot studies have included: • Protein quantification using OPA/NAC fluorescence – a collaboration between Great Ormond Street Hospital (GOSH) and University College London Hospitals (UCLH) and Bart’s & The London school of Medicine and Dentistry, Queen Mary University of London. • Protein quantification using epifluorescence scanning – University of Edinburgh/Royal Infirmary of Edinburgh. • Protein quantification using EDIC/epifluorescence microscopy – University of Southampton). Nigel Tomlinson described the technology using OPA/ NAC fluorescence as the ‘most simple’, yet ‘most graphic’ of the new techniques. He explained that the approach uses an imaging camera and a simple spray technique, which is very tolerant of ‘operational variables’, (such as the quantity of spray used and length of time before image capture), which makes it ‘very robust’. In addition, the technique studied at the University of Southampton has the ability to not only quantify protein, but also detect and quantify amyloids – the major component of plaque, which is associated with degenerative brain disease. “I do not know which of these technologies will prove to be the most suitable in the fullness of time and there is also alternative technology from Porton Down,” Nigel Tomlinson commented. However, he highlighted the need for protein detection technologies with very high levels of sensitivity: “We need to be getting down to attomole levels to make a big impact on the risk of vCJD transmission.” It is also important to be able to ascertain how much protein is present on an instrument – not simply to determine ‘pass’ or ‘fail’, he asserted, adding that there also needs to be an establishment of ‘a convention on calibration’. As part of this work, there needs to be agreement and standardisation on ‘units’ – are we talking about protein mass per unit area or per instrument? In addition, are we interested in the whole instrument or just the active surfaces – such as blades, which are in contact with the patient? There also needs to be discussion on whether a protein contamination limit could be established nationally or locally. He pointed out that the DH is more likely to take direction from organisations such as the IDSc on such matters and it is unlikely that decisions will be imposed by the Government, as they have been in the past.