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Can J Infect Dis Vol 12 No 6 November/December 2001
332
O
ver the past year, several situations have occurred in
Canada in which patients who had recently undergone a
surgical procedure were subsequently diagnosed with con-
firmed or suspected Creutzfeldt-Jakob disease (CJD). This
raised concerns over contamination of surgical instruments:
which instruments might have been contaminated from direct
exposure to tissues; can instruments become cross-contami-
nated by exposure to other contaminated instruments; what
assessment is necessary to determine cross-contamination;
and what should be done with instruments that have been
contaminated. Additionally, should there be a patient trace-
back in the face of potential but unproven exposure?
Unfortunately, there are no easy answers to most of the above
questions. Australia, the United Kingdom and the World
Health Organization have developed guidelines for the infec-
tion control management of patients with CJD, as well as
instruments and devices that come into contact with them and
their tissues (1-3). Health Canada’s draft CJD infection control
guidelines, withdrawn from the Health Canada Web site until
safety concerns regarding sodium hydroxide can be addressed,
closely mirrored recommendations made in those documents.
The Centers for Disease Control and Prevention guidelines for
CJD are under revision. However, a recent American publica-
tion made recommendations on what procedures should be
used for reprocessing items that have been in contact with the
prion protein (PrP) (4). These recommendations differ substan-
tially from the draft Canadian guidelines. This article reviews
current knowledge about CJD, and highlights some of the
infection control concerns and controversies.
WHAT IS CJD?
CJD is one of the transmissible spongiform encephalo-
pathies (TSEs), also known as prion diseases. These are
fatal degenerative brain diseases that occur in human and
certain animal species. The complete structure of the prion
has yet to be determined. It was originally thought that the
infectious agent was a slow virus or virus-like particle.
However, increasing amounts of evidence suggest that
unique agents, termed PrPs, are central in the etiology of
these diseases (5). The prion is theorized to contain only
protein, has no DNA or RNA and replicates by converting the
structure of the normal cellular PrP into an abnormal one by
a mechanism not yet known (5). The prion diseases are
characterized by microscopic intracellular vacuoles (spongi-
form degeneration), severe astrocytic gliosis and the deposi-
tion of prion amyloid plaques in the grey matter of the brain
(5). In animals, these diseases include scrapie in sheep and
goats, bovine spongiform encephalopathy in cattle, chronic
wasting disease in deer and elk, and transmissible mink
encephalopathy. In humans, four diseases were originally
identified as TSEs: CJD, Gerstmann-Sträussler-Scheinker
syndrome, fatal familial insomnia and kuru (1,5,6). Two
new forms of human TSEs have been recently identified:
variant CJD (vCJD) and sporadic fatal insomnia (6,7). All
forms of TSEs are experimentally transmissible, some across
species barriers (5,6,8).
Classical CJD is by far the most common human TSE,
although still very rare, with an estimated incidence of 0.5 to
1 case/million population/year. The clinical presentation usu-
ADULT INFECTIOUS DISEASE NOTES
Creutzfeldt-Jakob disease
and infection control
Lynn Johnston MD FRCPC
1
, John Conly MD CCFP FRCPC FACP
2
1
Queen Elizabeth II Health Sciences Centre and Dalhousie University, Halifax, Nova Scotia;
2
Departments of Pathology and Laboratory Medicine,
and Microbial and Infectious Diseases, Centre for Antimicrobial Resistance, Calgary Laboratory Services, Division of Microbiology, University
of Calgary, Calgary, Alberta
Correspondence and reprints: Dr Lynn Johnston, Room 5014 ACC, Queen Elizabeth II Health Sciences Centre, 1278 Tower Road, Halifax,
Nova Scotia B3H 2Y9. Telephone 902-473-8477, fax 902-473-7394, e-mail ljohnsto@is.dal.ca and Dr John Conly, Departments of
Pathology and Laboratory Medicine, and Microbial and Infectious Diseases, Centre for Antimicrobial Resistance, Calgary Laboratory
Services, Division of Microbiology, University of Calgary, 1638-10th Avenue SW, Calgary, Alberta T3C 0J5. Telephone 403-209-5338,
fax 403-209-5347, e-mail john.conly@cls.ab.ca
johnston.qxd 12/7/01 11:51 AM Page 332
ally begins with a progressive dementia that soon becomes
associated with cerebellar ataxia, visual deterioration,
myoclonus, and a variety of other neurological symptoms and
signs. The patient is usually mute and immobile in the termi-
nal stages. In most cases, death occurs within five months of
the onset of symptoms of CJD, with 80% dying within one year
(6). It is invariably fatal, and there is no treatment.
Three forms of classical CJD are recognized: sporadic,
familial and iatrogenic (infectious). The sporadic form, which
compromises 85% to 90% of all cases, occurs in the general
population with no identifiable cause, and typically affects
people between 55 and 75 years of age (3). The median age
of death for patients with sporadic CJD is 65 years. The famil-
ial form accounts for almost all of the remaining 10% to 15%.
In the familial form, there is generally an earlier age of onset
and a more protracted course (6). The iatrogenic form is very
rare, accounting for fewer than 1% of all known cases. It is
interesting to note that the clinical presentation of iatrogenic
forms may be somewhat different from sporadic CJD. A
review of cases of iatrogenic CJD indicated that cerebellar pre-
sentations predominated in recipients of pituitary hormone
and dura mater grafts (9). Although the clinical presentation
can contribute to an increased suspicion that a case is iatro-
genic, it cannot definitively distinguish iatrogenic from spo-
radic CJD. The incubation period for iatrogenic CJD also seems
to vary according to how it is acquired. From the observation
of cases in which CJD exposure was central (eg, direct appli-
cation of the CJD agent into the brain during neurosurgery),
the incubation periods are relatively short, ranging from 12
to 28 months (9,10). As the inoculation site moves further
away from the brain to other tissues, the incubation period is
extended. For example, incubation periods ranged from 1.5 to
18 years after exposure to contaminated dura mater (9).
Transmission from exposure through a peripheral route (as
with human growth hormone [hGH] injections) is associated
with an incubation period ranging from five to 30 years (9).
At this time, CJD cannot be readily diagnosed. There is no
diagnostic test available using easily accessible biological
tissue (11). The diagnosis is currently based on clinical fea-
tures and supportive investigations, and by postmortem
neuropathological examination. A definitive diagnosis is
established only by neuropathological examination (12).
Characteristic electroencephalogram (EEG) changes such as
the presence of triphasic periodic complexes are often of assis-
tance in making the diagnosis (12). However, repeated EEGs
may be required before the diagnosis can be made, and the
diagnosis cannot be excluded by one normal EEG. Magnetic
resonance imaging may show hyperintense signals in the
basal ganglia on T
2
-weighted images (6). A diagnostic test for
the detection of 14-3-3 protein in cerebrospinal fluid (CSF)
has high sensitivity (96%) and specificity (88%) for sporadic
CJD during the clinical illness (11). However, the predictive
value for a positive test is much lower. If you consider that
there may be a prevalence of 1%, the likelihood of a patient
with a positive test having CJD is only 49%. While helpful, the
test is most helpful when there is already a strong clinical
suspicion that the patient has CJD. The positive predictive
value reaches 99% and the negative predictive value reaches
95%, when the prevalence of disease is 50% (11). With famil-
ial CJD, typical EEG findings are often absent, and the 14-3-3
protein in CSF is found in only about one-half of cases (6).
WHAT IS vCJD?
vCJD was first recognized in the United Kingdom in 1996,
when it was noted by the CJD Surveillance Unit that 10
patients had neuropathological findings clearly distinguish-
ing them from classic CJD (7). As of September 2001, a total
of 110 definite and probable cases of vCJD have been identi-
fied worldwide: 106 cases in the United Kingdom, three cas-
es in France, and one case in the Republic of Ireland (13-15).
So far, no documented cases have been identified in Canada
by the Canadian CJD surveillance system (16); also, no cases
have been reported in the United States.
vCJD differs in several ways from sporadic CJD. Affected
individuals are younger (median age at death 29 years), and
the presenting features are often psychiatric and sensory
symptoms, followed by other neurological symptoms and pro-
gressive cognitive impairment (8,17). It tends to have a rela-
tively longer duration of illness than CJD, ranging from seven
to 38 months, with a mean of 14 months (14). The EEGs,
while not normal, do not show the ‘typical’ appearances
found in sporadic CJD (7). Magnetic resonance imaging brain
scans may show bilateral pulvinar high signals (14). Also, the
neuropathology in vCJD differs from sporadic CJD. It is charac-
terized by extensive PrP deposition with florid plaques mainly
throughout the cerebrum and cerebellum, surrounded by a
zone of spongiform change (7). The abnormal PrP molecular
strain type (type 4) is unique and distinctive in vCJD patients
(18,19). It has commonly been detected in lymphoreticular
tissues of these patients, but not in such tissues of patients
with other forms of CJD. Hence, vCJD can be diagnosed in the
appropriate clinical context by a tonsil biopsy (18,19). PrP
was found in the excised appendix of a 48-year-old man who
underwent an appendectomy eight months before developing
symptoms of vCJD (14). The presence of PrPs in lymphoreticu-
lar tissues poses additional infection control issues.
IATROGENIC CJD
CJD and other human TSEs are not known to spread by
contact from person to person, or by the airborne or respira-
tory route (3). However, transmission can occur during inva-
sive medical interventions (9). Worldwide, as of July 2000,
there had been 267 documented transmissions of CJD
between humans since the first report in 1974, and new cas-
es continue to appear (9). There are three circumstances in
which the transmission of CJD between humans has been
demonstrated: transplantation of central nervous system tis-
sue; the use of contaminated instruments during invasive
neurological or neurosurgical procedures; and peripheral
administration of human pituitary extracts. To date, all
known cases of iatrogenic CJD have resulted from exposure to
infectious brain, dura mater, or pituitary or eye tissue (4).
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Central nervous system tissue transplants include
corneal and dura mater grafts. In 1974, the first case of
iatrogenic CJD was reported in the recipient of a corneal graft
from a donor who had died of unsuspected CJD (9).
Experimental evidence demonstrated that corneas of infect-
ed animals could transmit CJD, and that the causative agent
spreads along visual pathways (20). To date, three cases of
corneal graft-related CJD have been reported, none of them
in Canada.
The first case of CJD in a recipient of a cadaveric-derived
dura mater transplant was reported in 1987 (21). As of July
2000, 114 cases had been reported worldwide, with four cases
occurring in Canada (9). Nearly all contaminated dura mater
were produced before 1987 by a single manufacturer whose
manufacturing processes were inadequate to inactivate the
CJD agent (22). Although the tissue preparation process was
modified in 1987, cases from earlier dura mater grafting
have continued to appear because of the long incubation
period (9). Commercial sources of human dura mater are now
closely monitored. However, stringent donor screening and
processing of dura mater may not completely eliminate the
potential for an infectious graft. Human dura mater is still
available in Canada, but hospitals that perform neurosurgery
also use synthetic materials, nondural human tissues and
animal tissues for dural repair (23).
The first report of CJD transmission to two patients as a
result of contact with direct brain instrumentation involving
electrodes previously used in the brain of a person with CJD
was published in 1977 (24). The electrodes had been
reprocessed with 70% alcohol and formaldehyde vapour
(4,6). Support for the conclusion that transmission was iatro-
genic followed from studies in which the same recording elec-
trodes were shown to transmit disease to experimental
primates (25). Retrospective studies have revealed four other
cases of probable iatrogenic transmission that occurred as a
consequence of neurosurgical procedures (9). It is presumed
that in these cases, the routine sterilization procedures of
instruments were insufficient to eliminate infectivity. Some
of the transmissions associated with reprocessed instru-
ments occurred several weeks after the instruments were ini-
tially exposed to tissues from a CJD patient. No such cases
have been reported in Canada. No cases related to neurosur-
gical instruments have been reported since the 1970s. To
date, there has been no evidence of CJD transmission related
to neurosurgical instruments used with patients who later
developed CJD or who are at risk for CJD but were asympto-
matic at the time of surgery (9).
In 1985, it was recognized that injected human cadaver-
extracted pituitary growth hormone could transmit CJD to
humans (26). Shortly thereafter, it was also recognized that
human pituitary gonadotropin administered by injection
could transmit CJD between humans (27). As of July 2000,
143 cases of CJD worldwide have been related to growth and
gonadotropic hormones of human origin (9). Due to the long
incubation period of CJD, it is likely that cases from earlier
exposure to hGH will appear in the years to come. In Canada,
where hGH was used from 1965 until April 1985, surveil-
lance for hGH-associated CJD has not identified any such
cases (9,28).
INFECTION CONTROL ISSUES AND CJD
Information describing the degree of infectivity for CJD
comes from experiments with animal TSEs (6). Different
organs and tissues have different infectivity levels in different
species (4,6). In general, the higher the concentration of the
CJD agent in the tissues of origin, the greater the assumed risk
of transmission. In all affected species, infectivity is greatest
in brain tissue, is present in some peripheral tissues but gen-
erally has been absent from all body fluids except CSF (6).
Information regarding human infectivity levels is limited, and
is extrapolated from experimental research on animals and
rare reports of iatrogenic exposure.
The CJD agent is hardy (as are all TSEs), remains infectious
for years in a dried state, and resists all routine sterilization
and disinfection procedures commonly used by health care
facilities (3,4,25,29). Similar to the situation of assessing
infectivity, much of the existing decontamination data has
come from studies of TSEs in animal populations (30). The
best defined model, scrapie in mice or hamsters, has been
repeatedly used in studies to establish practical inactivation
procedures. Specific parameters addressed have included the
levels of infectivity after exposure to particular chemicals, the
temperature range for inactivating the agent by steam sterili-
zation, and comparisons between prevacuum steam (porous
load) and gravity displacement sterilizers (30-34). Study
results have not been consistent for a variety of reasons: non-
standardized methods with a variety of tissues and varied
strains of TSE were chosen for the experiments (eg, intact
brain, dried macerated brain tissue or brain homogenates),
some strains were more thermostable than others, and varying
sample sizes with varying titres of infectivity were used
(4,29,35). It has been questioned whether the experimental
conditions are relevant to or reflect the clinical situation. Most
decontamination studies used high inoculums, tissue
homogenates that may protect the prion from inactivation and
organic matter on instruments that were not precleaned before
the decontamination process (4). It has been suggested that
the amounts of tissue used would exceed the bioburden nor-
mally found on surgical instruments (4,31). The limitations
and conflicting information complicate the extrapolation of
these findings to humans and hospital settings.
The current belief is that incineration completely destroys
the CJD agent. In the recently withdrawn draft Health Canada
guidelines, incineration was recommended as the safest and
most unambiguous method for ensuring that there is no risk
of residual infectivity on surgical instruments that have
become contaminated with the CJD agent. The American rec-
ommendations are less conservative in their approach,
believing that thorough instrument cleaning removes suffi-
cient proteinaceous material to allow conventional steriliza-
tion methods (4). However, evidence suggests that
instruments not precleaned before sterilizing may still har-
Adult ID Notes
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bour the CJD agent in the centre of the tissues or fluid
remaining on the instruments (9). It is believed that the ster-
ilization process may seal the outer layer of the tissues that
remains on the instruments, which consequently protects the
CJD agent in the core of these particles (36). Furthermore,
studies that evaluate the efficacy of a combination of clean-
ing and sterilization in the clinical setting have not been pub-
lished (4).
Chemical processes include the use of either sodium
hypochlorite or sodium hydroxide, which have both been
found to be effective in decreasing the infectivity of prions
(4,30,34,37). In one study, an unexplained and unexpected
finding associated with sodium hydroxide was that with
bovine spongiform encephalopathy and scrapie agents, 2 h
exposures were less effective than 30 or 60 min procedures
(30). In the concentrations required, both of these agents are
damaging to instruments and caustic or noxious to health
care workers (38,39).
Gravity displacement and prevacuum (porous load) steam
sterilizers have been tested using various temperatures and
total cycle times (4,30,34,37). However, the results are also
contradictory, with some reports showing complete inacti-
vation of the prion and other reports showing incomplete
inactivation with both prevacuum (porous load) and gravity
displacement steam sterilizers (4,29,30,35,37). While
acknowledging the disagreement about the ideal time and
temperature cycle, the American publication recommends the
following as reasonable on the basis of the scientific literature:
121°C to 132°C for 60 min for gravity displacement sterilizers
and 134°C for 18 min or longer for prevacuum sterilizers (4).
Combination methods are not recommended. The World Health
Organization recommends 1 h for both the gravity and prevac-
uum sterilizers in combination with a chemical process if the
contaminated item is not incinerated (3).
In the face of limited and contradictory findings, and varied
recommendations, it may be difficult to know what decision to
make when it comes to handling equipment that is (or poten-
tially is) contaminated with PrP. Regardless of what comes in
future recommendations, some degree of uncertainty will con-
tinue to exist. If cost was not an issue, there would be little dif-
ficulty in making a decision. While we await the publication of
guidelines, however, preventive and risk management strate-
gies can be considered. Consideration should be given to sepa-
rately reprocessing instruments that come into contact with
high risk tissues from other instruments to minimize the
amount of cross-contamination should an initially unrecog-
nized exposure occur. Better methods of instrument tracking
are required to facilitate a postexposure workup. A 1998 survey
of Canadian hospitals doing neurosurgical procedures found
that none of the 19 respondents obtained risk factors for CJD on
the preoperative questionnaire, and only 50% could adequately
quarantine instruments if necessary (23). Clinicians and infec-
tion control practitioners need to work more closely to identify
patients with confirmed or suspect CJD, so that the first clue to
the diagnosis does not come when the patient is in the recovery
room or three days later when the patient is on the ward (40).
Adult ID Notes
Can J Infect Dis Vol 12 No 6 November/December 2001
335
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