Dental treatment and risk of variant CJD – a case control study
D. Everington,1 A. J. Smith,2 H. J. T. Ward,3 S. Letters,4 R. G. Will5 and J. Bagg6
Objective Knowledge of risk factors for variant CJD (vCJD) remains
limited, but transmission of prion proteins via re-useable medical devices,
including dental instruments, or enhanced susceptibility following trauma
to the oral cavity is a concern. This study aimed to identify whether
previous dental treatment is a risk factor for development of vCJD.
Design Case control study.
Methods Risk factor questionnaires completed by interview with
relatives of 130 vCJD patients and with relatives of 66 community and
53 hospital controls were examined by a dental surgeon. Responses
regarding dental treatments were analysed.
Results We did not find a statistically signifi cant excess of risk of vCJD
associated with dental treatments with the exception of extractions in
an unmatched analysis of vCJD cases with community controls
(p = 0.02). However, this result may be explained by multiple testing.
Conclusions This is the first published study to date to examine
potential links between vCJD and dental treatment. There was no
convincing evidence found of an increased risk of variant CJD
associated with reported dental treatment. However, the power of the
study is restricted by the number of vCJD cases to date and does not
preclude the possibility that some cases have resulted from secondary
transmission via dental procedures. Due to the limitations of the data
available, more detailed analyses of dental records are required to fully
exclude the possibility of transmission via dental treatment.
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DISCUSSION
Many studies have searched for risk factors for the development
of different types of CJD, such as diet, exposure to
animals, surgical treatment, including dentistry, and occupational
exposures. A retrospective case control study15 of 60
definite cases of sporadic CJD, occurring in Japan between
1975 and 1977 found no association with extractions of maxillary
or mandibular teeth. An analysis of 26 sporadic CJD
cases and 40 matched controls from the United States16 failed
to discover a significant odds ratio for endodontic surgery,
though these workers did note statistically significant odds
ratios for intraocular pressure testing, injury to or surgery on
the head, face or neck and trauma to other parts of the body.
However, these findings suffer from low statistical power and,
in the case of the Japanese paper, information was requested
for extractions only during the fi ve year period prior to onset.
This paper attempts to identify an association between vCJD
and reported dental treatment.
Comparison of the reported dental histories of cases and
controls found that extractions were the only dental risk factor
that reached statistical significance (at the 5% level) in the
unmatched analysis with community controls. This may be a
result of multiple testing especially as there are fewer extractions
in the cases than in the hospital controls. It is likely that
the majority of vCJD cases in this cohort were infected through
eating BSE contaminated meat products. Therefore, it is diffi -
cult to detect a small subgroup that may have been infected by
secondary transmission, as in this study, through dentistry.
There are a number of limitations to this study, most importantly
relying on reported data from relatives and the relatively
small numbers of cases and controls resulting in low
power to detect statistical differences. Recruitment of controls
has been problematic,17 although every effort was made to
maximise this group. Selection of controls was not matched for
demographic and socio-economic factors for dental attendance
and this may have resulted in bias. It is possible that some of
the responses of ‘no known treatment’ reflect poor knowledge
or recall on the part of the relatives. This would reduce the
power of the study to pick up significant differences between
groups, but not necessarily introduce bias.
Whilst these preliminary data on a topic of great concern
for public health do not provide evidence supporting reported
dental work as being a major route of transmission of the BSE
agent to humans to date, they do not preclude the possibility
that some vCJD cases have been infected by this route.
Furthermore, the incubation period following infection by
a peripheral route may be relatively long and therefore the
period of observation to date of potential secondary transmission
of vCJD may be too short to detect cases.
A more detailed study of previous treatment based on reviewing
actual dental records rather than relying on reported treatments
is required to gain a wider insight into the dental history
of both cases and controls. We are currently investigating the
possibility of examining dental records of vCJD cases and a
larger group of unmatched controls.18
The National CJD Surveillance Unit is funded by the Department of Health
and the Scottish Executive Department of Health. The sponsors of the study
had no role in study design, data collection, data analysis, data interpretation,
or in the writing of the report. We are also grateful to the families of
cases, without whose co-operation this study would not have been possible.
FULL TEXT ;
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