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From: TSS ()
Subject: SEAC Position statement vCJD and Endodontic dentistry
Date: May 8, 2006 at 6:45 am PST

CJD WATCH MESSAGE BOARD
TSS 2005
SEAC Position statement vCJD and Endodontic dentistry
Mon May 8, 2006 09:08
68.238.108.206

SEAC
Position Statement

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Position statement vCJD and Endodontic dentistry
Issue

1. The Department of Health (DH) asked SEAC to advise on the findings and implications of a preliminary risk assessment of potential vCJD transmission via endodontic procedures (dental procedures involved in the maintenance of dental pulp and the treatment of the pulp cavity) 1. This is particularly pertinent because of the large number of endodontic procedures undertaken in the UK.

Background

2. There are no reported definite or suspected cases of vCJD transmission arising from dental procedures. However, prions are more resistant than other types of infectious agent to the conventional cleaning and sterilisation practices used to decontaminate dental instruments 2. Therefore, should dental instruments become contaminated from tissues in the oral cavity of infected individuals, there is a risk of transmission to subsequent patients.

3. A quantitative DH risk assessment 3, accepted by SEAC in 2003, considered two possible mechanisms for the transfer of vCJD infectivity via dental instruments: (i) accidental abrasion of the lingual tonsil, known to carry infectivity in vCJD cases; and (ii) contact with dental pulp that evidence from animal studies suggested may be infective. On the basis of the information available, the DH analysis suggested that the risk of transmission to individual patients via accidental abrasion of the lingual tonsil is very low. Furthermore, should dental pulp be infective, the risk of transmission via endodontic procedures, although higher, is also low. Although a very large number of dental procedures are conducted, the relative risk to public health from potential transmission via dental, compared with hospital, surgery was considered to be relatively low.

4. In 2006, SEAC considered a new preliminary risk assessment by DH of the risks of vCJD transmission via endodontic procedures, taking into account new information on decontamination of dental instruments, the potential infectivity of dental pulp, and the possible existence of subclinical vCJD carrier cases.

Endodontic instruments

5. Evidence suggests that the files and reamers used in endodontic procedures are reused and are difficult to reliably decontaminate 4. Appreciable quantities of residual material remain adherent to the surface after normal cleaning and sterilisation 5. Thus, there is potential for transfer of dental pulp between patients undergoing endodontic procedures.

vCJD infectivity in dental tissues

6. There are no data on vCJD infectivity in dental pulp. Although no abnormal prions were found in a study of dental tissues, including dental pulp, from vCJD cases 6, dental pulp includes blood and peripheral nerve tissue known to carry vCJD infectivity 7,8. In addition, appreciable infectivity has been found in the dental pulp of hamsters with hamster scrapie 9. Although it is possible that the peripheral nerve may only become infective close to, or after, the onset of clinical vCJD, inflammation may promote the propagation of prions 10. Thus, although the data are limited and indirect, it is reasonable to assume that the dental pulp of individuals subclinically-infected with vCJD may be infectious although the level of infectivity is unknown. Studies underway will provide direct data on the infectivity in dental tissues from vCJD cases.

Subclinical carrier state

7. A study of humanised mice showed that vCJD infections may not always progress to clinical disease within the normal lifespan of the animals 11. Another study suggested that prion infections in mice that remain at a subclinical level can be transmitted to other mice, resulting in clinical disease 12. Thus, there is evidence to suggest that individuals infected with the BSE / vCJD agent may remain in a subclinical infection carrier state instead of developing vCJD. A discrepancy between prevalence estimates based on a survey of abnormal prion protein in appendix and tonsil tissue and data on vCJD cases supports this hypothesis 13. As no diagnostic test exists to identify such individuals, they could over the course of their lives be potential sources of numerous secondary infections arising from invasive medical or dental procedures.

8. The prevalence of subclinical infection in the UK population is uncertain. A recent estimate suggests the number of subclinical carriers may be of the order of several thousand 14. SEAC has strongly recommended that further studies to ascertain better the prevalence of vCJD infection be urgently considered 15.

Transmission risks

9. The new DH analysis suggests that, on the basis that residual dental pulp on endodontic files and reamers is transferred relatively efficiently to patients on reuse, dental pulp is as infective as peripheral nerve tissue and a subclinical carrier population for vCJD exists, a self-sustaining vCJD epidemic arising from endodontic surgery is plausible. There are uncertainties about the efficiency of vCJD transmission via endodontic procedures, the vCJD infectivity of dental pulp and the existence of a subclinical infection carrier state. However, even if a self-sustaining epidemic were not possible, clusters of vCJD infections could arise from the use of instruments contaminated with the vCJD agent from endodontic procedures on infected patients. Interactions between this and other routes of secondary transmission, such as blood transfusion and hospital surgery, would make a self-sustaining epidemic more likely.

Potential risk reduction measures

10. Endodontic files and reamers have a limited lifespan, restricting the number of possible secondary transmissions. Improving the effectiveness of procedures used to decontaminate dental instruments would reduce the risk of transmission. Restricting endodontic files and reamers to single use would prevent potential secondary transmission via these instruments.

Conclusions

11. A preliminary risk assessment produced by DH suggests that vCJD transmission via endodontic dentistry may, under certain hypothetical but plausible scenarios, be sufficient to sustain a secondary vCJD epidemic. However, there are uncertainties around the data and assumptions underpinning the assessment. Research underway will address some of these uncertainties and allow the risk assessment to be refined. Once the research is complete and / or other data become available, the risks should be reassessed. A watching brief should be maintained.

12. It is unclear whether or not vCJD infectivity can be transmitted via endodontic files and reamers. However, given the plausibility of such a scenario and the large number of procedures undertaken annually, it would be prudent to consider restricting these instruments to single use as a precautionary measure. Since sufficiently rigorous decontamination of these instruments is difficult, single use of these instruments would eliminate this risk, should it exist.

SEAC
May 2006


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1. Department of Health. Dentistry and vCJD: the implications of a “carrier state” for a self-sustaining epidemic due to endodontic dentistry. A Preliminary Risk Assessment. Unpublished.
2. Smith et al. (2003) Prions and the oral cavity. J. Dent. Res. 82, 769-775.
3. Department of Health. (2003) Risk assessment for vCJD and dentistry.
4. Letters et al. (2005) A study of visual and blood contamination on reprocessed endodontic files from general dental practice. Br. Dent. J. 199, 522-525.
5. Smith et al. (2005) Residual protein levels on reprocessed dental instruments. J. Hosp. Infect. 61, 237-241.
6. Head et al. (2003) Investigation of PrPres in dental tissues in variant CJD. Br. Dent. J. 195, 339-343.
7. SEAC 91 minutes paragraph 9. www.seac.gov.uk/papers/papers.htm
8. Department of Health (2005) Assessing the risk of vCJD transmission via surgery: an interim view. Unpublished.
9. Ingrosso et al. (1999) Transmission of the 263K scrapie strain by the dental route. J. Gen. Virol. 80, 3043-3047.
10. Heikenwalder et al. (2005) Chronic lymphocytic inflammation specifies the organ tropism of prions. Science. 307, 1107-1110.
11. Bishop et al. (2006) Predicting susceptibility and incubation time of human-to-human transmission of vCJD. Lancet Neurology.
12. Hill et al. (2000) Species-barrier-independent prion replication in apparently resistant species. Proc. Natl. Acad. Sci. USA. 97, 10248-10253.
13. SEAC Epidemiology Subgroup (2005) Position statement on the vCJD epidemic. www.seac.gov.uk/statements/state260106subgroup.htm
14. Clarke & Ghani. (2005) Projections of future course of the primary vCJD epidemic in the UK: inclusion of subclinical infection and the possibility of wider genetic susceptibility. R. J. Soc. Interface.
15. SEAC (2005) SEAC response to the SEAC Epidemiology Subgroup statement on the vCJD epidemic. www.seac.gov.uk/statements/state260106.htm


Page updated: 8th May 2006

http://www.seac.gov.uk/statements/statement0506.htm

TSS





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