Risk assessment for vCJD
Document type: Publication Author: Department of Health. Economics and Operational Research Division Published date: 1 July 2003 Primary audience: Professionals Gateway reference: 2003 Pages: 27 Copyright holder: Crown This report analyses the potential risk of vCJD transmission through re-use of instruments in dental surgery. Based on an existing EOR model for hospital surgery, the analysis considers a wide range of scenarios to allow for multiple uncertainties. It covers procedures carried out in "high street" dental practice, rather than more specialised maxillo-facial surgery.
If patients are recognised as being at heightened risk of infection with any form of CJD, instruments used on them are already subject to special precautions against onward infection, being quarantined and if necessary destroyed. However this analysis concerns potential risks of transmission amongst the generality of patients, where instruments might unknowingly be used on someone incubating vCJD. Two potential transmission routes are considered:
Expert consultation suggested an initial focus on the possibility of transmitting infection through accidental abrasion of an infective patient's lingual tonsils, these being the only relevant oral tissue for which there is direct evidence of vCJD infectivity in humans. Most of this analysis focuses on this topic.
However, vCJD infectivity in other tissues encountered in dentistry - e.g. dental pulp - is implied by some animal models. Though such infectivity has not so far been detected in humans, the possibility cannot be ruled out. Furthermore there is evidence that some instruments used in endodontic surgery - e.g. files and reamers - are particularly difficult to clean, and may carry significant residues of material after washing. We therefore also include some illustrative calculations of the transmission risks that could be posed if this residue were to carry vCJD infectivity. It should be stressed that this part of the analysis is purely hypothetical.
Risks to individual patients
On present evidence and advice, the chance of vCJD being transmitted via tonsillar abrasion appears remote. The previous analysis of hospital surgery provides some points of comparison. For example, if similar standards of instrument decontamination are achieved in the two settings:
With assumptions about tissue abrasion as suggested by expert consultation, a single dental procedure on an infective patient would be about 1,000,000,000 times less likely to transmit vCJD than - say - a tonsillectomy. (The latter in turn would be much less likely to do so than a procedure involving the Central Nervous System or the back of the eye.)
Even with very pessimistic assumptions about the chances of tissue abrasion, a differential of about 10,000-fold with tonsillectomy would remain.
If tissues such as dental pulp were to be infective, the risks of transmitting vCJD would obviously increase. However the analysis suggests that even taking a pessimistic scenario, the risks per operation would still be low (at least 10 times lower than for a tonsillectomy).
Risks to public health
Any risk of transmission depends critically on the initial prevalence of the disease and the number of invasive dental procedures. As the former is unknown, a range of scenarios is considered. The number of dental procedures in the UK is very large - estimated at about 75 million annually, including both NHS and private treatment. Of these, around 2 million are endodontic procedures. Even so, any risk to public health posed by dental transmission appears small compared to that for hospital surgery in similar scenarios.
Risk reduction measures
As for hospital surgery, the key consideration in minimising any risk of transmission is assuring the efficacy of instrument decontamination, even though current methods cannot remove such risks completely. In line with existing SEAC advice, potential risks can be further reduced by introduction of more single-use instruments where appropriate, especially of difficult-to-clean items.
Qualification of analysis
Almost all the analysis reported
here is subject to two major caveats. The first is that decontamination procedures
used in "high street" dentistry are not (in general) significantly
less effective than has been assumed here. Though the assumptions used are intended
to give fairly conservative estimates for the reductions in infectivity achieved,
this continues to be an area of uncertainty. It therefore remains important
to monitor actual decontamination practice and encourage its improvement.
Source: Department of Health (DH) , UK