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News Bulletin : ADA News Bulletin April 2011
18 APRIL 2011 Dental tissues taken from vCJD patients show no evidence of the abnormal prion protein associated with infectivity. In other words, teeth, gingival tissues, dental pulp and oral mucosal tissues in infected patients do not contain the vCJD infective agent – the nearest location is the tonsils. It appears that large doses of blood are required for vCJD transmission – in the scale of transfusions, rather than droplets of blood or traces of protein residue. 4,5 The at-risk patients for vCJD are therefore haemophiliacs and others who receive frequent large volume transmissions of blood and blood products. The limitations applied by the Australian Red Cross Blood Service reduce the risk of vCJD transmission through blood transfusion in Australia. There are only four known cases of vCJD in the UK which have been attributed to receiving a transfusion from a vCJD-infected donor of blood or plasma, of which one was a haemophiliac who had received multiple transfusions. In contrast, there is no evidence of transmission of classical forms of CJD (sporadic, medically acquired or genetic forms) through exposure to blood or blood products. There is currently no evidence of vCJD having been spread by dentistry, despite between 65–73 million dental procedures being carried out annually across the UK. Modelling of the probability of transmission has shown that even in a worst case dental scenario a single dental instrument carrying the agent would have a likelihood of transmitting vCJD of less than 1 in 10,000, and for a set of 10 instruments less than 1 in 1,000. It has been calculated that based on 70 million invasive dental procedures in the UK per year in a population with 1 patient in 10,000 carrying vCJD, and all such patients presumed to be infective, that there would be 7,000 procedures per year on infective patients. Following the statistics above, a per-operation transmission risk of 0.5 per 1,000 would then lead to about 3.5 expected infections per year, within the population – yet no such transmissions have even been documented to occur in the UK. UK studies which have compared patients with vCJD having dental treatment with matched controls did not show that having dental work represents a major route of vCJD transmission. There have been a small number of reported cases of patients in the UK diagnosed with vCJD who have been infected through blood transfusion. The Australian Red Cross Blood Service has implemented policies to reduce the risk of vCJD transmission through blood transfusion in Australia. Currently, they exclude people from donating who have resided in the UK between 1980 and 1996 for a total (cumulative) time of six months or more, or have received blood transfusions in the UK since 1 January 1980. Because of this, the possibility of multiple transmission events occurring from transfusion in Australia can be discounted. Recent medical research has led to the development of what may be a reliable blood screening test for vCJD. On 4 February 2011, media attention was captured by announcements in the Lancet of the world’s first accurate blood test for vCJD. The test, which was developed by UK Medical Research Council is 100,000 times more sensitive than any previous attempt, and could transform the diagnosis and screening of this condition.6 The assay has sensitivity for vCJD of over 71% (Confidence Interval 48–89%) and a specificity of 100% (Confidence Interval 98–100%). Laurence J Walsh On behalf of the Infection Control Committee REfEREnCES References supplied by the author are available on request by contacting firstname.lastname@example.org committee report
ADA News Bulletin March 2011
ADA News Bulletin May 2011