Assessing the risk of Creutzfeldt-Jakob disease

The risk of contracting the deadly Creutzfeldt-Jakob disease at work is still unknown, but health protection bodies consider the threat serious enough to require a register to monitor exposure. Occupational health practitioners have a key role to play, says Katie Oakley.

Currently, the risk of workplace exposure to transmissible spongiform encephalopathies (TSEs) in laboratory and healthcare workers is unknown. It is possible that some cases of Creutzfeldt-Jakob disease (CJD) could be occupationally acquired. In order to find out more about this, the Health Protection Agency (HPA), working with the National CJD Research and Surveillance Unit (NCJDRSU), has set up an occupational exposure registry.

The HPA will gather details on exposed workers from OH professionals and cross-check these with the NCJDRSU data on all reported CJD cases in the UK. OH professionals covering laboratory and healthcare workers potentially exposed to TSE-infected tissues therefore need to be aware of the register and their crucial role in reporting and managing incidents.

The registry of occupational exposure to CJD and other TSEs in healthcare and laboratory workers was established in August 2011. Although there is currently no evidence of occupational transmission of TSEs, it does remain a possibility. And it is only by systematically gathering and analysing information over the coming years that the evidence base behind national guidelines for healthcare and laboratory workers can be strengthened.

This article provides an overview of the main types of CJD, the national bodies involved and the background to setting up this registry. Links are provided to more detailed information about the registry, the practical implications of the registry for OH professionals and sources of further information on TSEs.

Prion disease

CJD is a degenerative neurological disorder that is incurable and inevitably fatal. While often referred to as the human form of mad cow disease, the classic form of CJD is not related to bovine spongiform encephalopathy (BSE). CJD was first described in the 1920s by German doctors Creutzfeldt and Jakob. Sporadic CJD has a worldwide incidence of 1:1,000,000, with around 60 new UK cases a year. Far fewer people are affected by the three other types of CJD: variant CJD (vCJD); iatrogenic CJD, caused by medical treatment; and inherited CJD, also known as genetic or familial CJD. The infective agent in TSEs is generally agreed to be an abnormal form of prion protein, which accumulates in the brain.

Most OH professionals will never encounter anyone with CJD because it is so uncommon. There is no diagnostic blood test or cure for this fatal type of TSE and while the incubation period can be prolonged, disease progression following diagnosis is not. Workplace rehabilitation is thus highly unlikely to be an option.

Even though the disease is so rare, there are several statutory bodies involved with CJD in the UK. In addition, there are voluntary organisations such as the CJD Support Network. The NCJDRSU monitors all suspected cases of prion disease and researches possible causes of and developments in CJD.

The National Prion Clinic at the National Hospital for Neurology and Neurosurgery is where people with suspected or confirmed prion disease are referred and it cares for people with or at risk of inherited prion disease. People who developed CJD after receiving human-derived pituitary growth hormone to correct growth problems are cared for by the Institute of Child Health in London.

quotemarks The incidence of vCJD has been far lower than predicted by statistical modelling exercises.”

The HPA Centre for Infections (CJD section) hosts the occupational exposure registry. The HPA also conducts studies to establish the prevalence of pre-clinical vCJD infection by laboratory examination of stored human tissues for abnormal prion protein.

Worldwide attention focused on CJD for the first time in 1996 when vCJD was identified in the UK. Epidemiological evidence suggested a link with an outbreak of BSE. UK case control studies found that the most likely cause of vCJD was the consumption of BSE-contaminated beef products.

Despite the potential exposure of most of the UK population to contaminated beef products, the incidence of vCJD has been far lower than predicted by statistical modelling exercises. Some 176 people have been diagnosed with probable or definite vCJD and they have all died. The peak of the epidemic was in the year 2000. It is possible there could be future epidemics, but there is no evidence of this at present.

Emerging science

Although the infective agent in TSEs is generally agreed to be an abnormal form of prion protein and it is known that CJD is invariably fatal, uncertainties remain in a range of areas, including the mode of transmission, the incubation period (which can be prolonged) and variations in individual and genetic group susceptibility. Moreover, it is possible that some of the UK population have pre-clinical infection following exposure to contaminated beef products during the BSE epidemic, and they could pose an infection risk to others.

Prion proteins are very sticky and infectivity cannot be removed – only reduced – by the currently available decontamination procedures used for surgical instruments. There have been a handful of cases of transmission of sporadic CJD by surgery and tissue transplant. Transmission of vCJD via surgery has not been reported, but is believed to be a risk. Three vCJD cases and an individual with presumed pre- or sub-clinical infection received transfusions (in 1999 or earlier) from blood donors subsequently found to have vCJD. There have been no cases of transmission of other types of CJD by blood transfusion, only vCJD.

The likely risk of secondary transmission of CJD in the UK is unknown. It would be helpful to know the percentage of the population with pre-clinical infection to assist the planning of national public health policy, but as there is no blood test available to identify people who may have been infected the UK prevalence of pre-clinical infection with vCJD is unclear. The HPA’s large study of tonsil tissue suggested a prevalence of 1:10,000 of the UK population. A subsequent project assessed appendiceal tissue and gave a central estimate of prevalence (with large confidence intervals) of 1:2,000. This is the prevalence estimate used by the TSE risk management subgroup of the Advisory Committee on Dangerous Pathogens (ACDP).

TSE risk management subgroup

This subgroup of the Department of Health’s ACDP advises the Government on TSEs. As with all risk management, experts adopt a precautionary approach in an area of scientific uncertainty. The subgroup reviews the emerging science and updates its advice accordingly.

The key website for practical and detailed infection control guidance on TSEs is produced and regularly updated by the TSE risk management subgroup. The subgroup also recommended the establishment of the occupational exposure registry. The HPA CJD section will provide periodic reports on the registry to the subgroup.

Incident registry

Prior to August 2011, there was no structured collection system for occupational exposure incidents to CJD and TSEs. Now, exposure incidents can be reported to the registry. The HPA protocol for registering exposure to CJD and other TSEs defines an exposure incident as: “For healthcare workers: Percutaneous or muco-cutaneous inoculation of tissues or blood from probable or confirmed cases of all types of human prion diseases including CJD. For laboratory workers: Percutaneous or muco-cutaneous inoculation of tissues or blood from TSE-infected animals or tissues.”

quotemarks It is the OH professional who must ensure that the exposed worker has all the information they need about why the registry has been established and what will happen to their personal identifiable information.”

Reporting exposure

Laboratory workers are aware that they work in potentially hazardous environments. They are trained in safe working practices and operate according to tight procedures in controlled environments. Likewise, healthcare workers should be aware of the latest infection control advice when caring for patients. Nevertheless, as OH professionals know only too well, in occupations where it is not possible to eliminate hazards, the potential for accidents exists.

In the event of a TSE exposure incident, the TSE risk management subgroup first-aid advice is as follows: “For any accident involving sharps or contamination of abrasions with blood or body fluids, wounds should be gently encouraged to bleed, gently washed (avoid scrubbing) with warm soapy water, rinsed, dried and covered with a waterproof dressing, with further treatment given appropriate to the type of injury. Splashes into the eyes or mouth should be dealt with by thorough irrigation. The accident should be reported as defined in local practice, and an accident or incident form completed.”

Exposure incidents can be reported to the HPA registry. The HPA has sent information about the registry to its existing OH professional contacts, who participate in the long-established national blood-borne virus surveillance scheme, to neurosurgical centres and to research laboratories working with TSE-infected animals or tissues.

OH professionals are responsible for liaising with the HPA over consent forms, exposure history forms and information leaflets. Crucially, it is the OH professional who must ensure that the exposed worker has all the information they need about why the registry has been established and what will happen to their personal identifiable information. Importantly, the HPA information states that being enrolled on this registry should not have any effect whatsoever on peoples’ daily lives and reassurance is given concerning the stringent controls in place to protect this data.

Awareness

Although the registry has been running for almost two years, it seems that awareness within the OH arena about CJD may need to be raised.

Andrea Paterson, professional head of OH at Nuffield Health, says: “From an OH perspective, CJD really has very little impact because we rarely come across it. I have heard about the registry though and CJD regularly reaches our group infection prevention committee as a topic for discussion in relation to updating our policies in line with changes in national guidance.

quotemarks Other than keeping the records for 40 years – as we would in any other health surveillance programme – we decided there was nothing else we needed to do.”

Andrea Paterson, Nuffield Health

“We have put a section in the CJD Infection Prevention Policy about the management of healthcare workers. This involves making a note of any staff involved in a procedure where instruments have been isolated and keeping these records for 40 years. So, other than keeping the records for 40 years – as we would in any other health surveillance programme – we decided there was nothing else we needed to do.”

Deborah Mathews, OH and safety manager at University College London Hospitals NHS Foundation Trust, says: “Despite having the National Hospital for Neurology and Neurosurgery as part of the trust, we have not had any occupational exposures to blood or body fluids incidents reported where exposure to CJD has occurred in the last few years. We therefore have not needed to refer to the register. As this is likely to be a very rare occurrence, regular reminders to staff about the existence of the register would be helpful.”

Field investigations

OH professionals may be involved in assisting with retrospective investigations when the NCJDRSU discovers that a person who developed CJD had an occupational history of working in a healthcare or laboratory setting. Such look-back exercises may include field investigations where an HPA scientist visits the hospital or laboratory concerned to scrutinise records, talk to staff and try to ascertain whether any TSE exposures have occurred. They may wish to examine OH records for relevant information.

Conclusion

The registry of occupational exposure to CJD and other TSEs in healthcare and laboratory workers contains information on healthcare and laboratory workers who have sustained an occupational exposure.

Its objectives are to standardise reporting, establish a central database and monitor the risk of CJD in healthcare and laboratory workers.

Gathering information in areas of emerging science is fundamentally important in the development of a long-term public health strategy. Many uncertainties remain regarding TSEs, and this registry will contribute information in the area of TSE and occupational risk. When OH professionals are involved in these rare incidents, they will have an important role to play in reporting and managing them.

Katie Oakley is editor of Occupational Health Nursing.