A wide variety of other bacteria, viruses, fungi and protozoa could potentially be transmitted by endoscopy. Relatively little investigation has been undertaken in this area although candidal infection of immunocompromised patients has been reported. An epidemic of pseudoinfection with the yeast Rhodotorula rubra has been reported in bronchoscopy patients.
The sensitivity of many unusual organisms to chemical disinfectants is largely unknown. However some agents such as the oocysts of Cryptosporidia are highly resistant to a variety of chemical disinfectants including 2% glutaraldehyde. It is unlikely that such organisms pose a significant threat to patients with normal immune systems but they could be responsible for serious and even fatal infections in the immunocompromised.
Meticulous mechanical cleaning has been shown to remove approximately 104 organisms of Cryptosporidium parvum and this combined with the fact that C. parvum viability is reduced by 103 within 30 minutes on dry surfaces indicates that a properly processed endoscope does not pose a risk of transmitting this organism.
PRIONS
This is a proteinaceous infectious agent or prion protein, which accumulates in neural cells. No prion-specific nucleic acid is known to b required for transmission of disease.
Kodachrome courtesy of Tony Tannenberg, QML
Disease
Transmissible spongiform encephalopathies (TSEs), also
known as prion diseases are fatal degenerative brain diseases that occur
in humans and certain animal species. These diseases are characterised
by the accumulation of a modified prion protein in the grey matter of
the brain.
Human TSEs occur in sporadic, familial, iatrogenic and variant forms and they include:
-
Classical Creutzfeldt-Jakob disease (cCJD)
-
Variant CJD (vCJD)
-
Gerstmann-Straussler-Scheinker Syndrome (GSS)
-
Fatal Insomnia (FI)
-
Kuru
Mode of Transmission
Sporadic disease accounts for 90% of known cases and the
mode of acquisition and/or transmission is not known. Less than 10% of
cases are familial. The "variant" CJD disease (vCJD) has been connected
to beef contaminated with the bovine spongiform encephalopathy (BSE)
agent. There have been no reports of vCJD in Australia.
Iatrogenic CJD has been described in humans in 3 circumstances:
-
after use of contaminated medical equipment
-
after use of extracted pituitary hormones or gonadotrophin
-
after implantation of contaminated grafts of dura mater or cornea
The risk of CJD transmission is a function of the
infectivity of the particular tissue, which relates to the concentration
of the abnormal prion protein in that tissue.
-
High infectivity tissue - brain, spinal cord, eye, pituitary gland
-
Low infectivity tissue - CSF, kidney, liver, lung, lymph nodes, spleen, placenta, uterus, dorsal root ganglia, trigeminal ganglia
-
No detectable infectivity - peripheral nerve, intestine, bone marrow, blood, thyroid gland, adrenal gland, heart, skeletal muscle, adipose tissue, gingiva, prostate, testis, tears, nasal mucus, saliva, sweat, urine, faeces, semen, serous exudate and milk.
Standard Precautions should apply to the routine
management of patients. Additional precautions may be required for
reprocessing some surgical instruments used for high risk patients.
Significance in Endoscopy
TSE agents exhibit an unusual resistance to conventional
chemical and physical decontamination methods. In addition, the
catastrophic nature of the disease has engendered such an emotional
response that many recommended risk containment strategies have been
grossly excessive. It again needs to be stressed that no iatrogenic or occupationally acquired CJD has occured from exposure to low or no risk tissues.
Accordingly to the tissues listed in the categories
above endoscopes would be contaminated only with material from the "no
detectable infectivity" category. This would indicate that standard
cleaning and high-level disinfection protocols would be adequate for
reprocessing. Although there is an assumption there is no risk,
generally a cautious approach is taken in this situation.
The recommendations that are consistent with the CDNA guidelines are:
-
Seek alternative diagnostic studies or therapeutic approaches in patients with known, or a higher risk of, CJD.
-
Where such procedures are totally unavoidable seek expert advice from the state health department or an infectious diseases physician.
-
Accessory items used in patients with known, or a higher risk of, CJD shall be single use only items.
-
No change can be recommended to the indications for endoscopy or current cleaning and disinfection protocols in patients who have no increased risk of CJD.
The following matrix determines when it is necessary to
apply additional precautions over and above recommended standard
(routine) precautions for endoscopic procedures.
| Patient-risk categories | High-infectivity tissue exposed | Low-infectivity tissue exposed |
|
High-risk Patients with a definite risk of cCJD infection (generally showing neurological symptoms) |
Additional precautions required | Standard precautions |
|
Low-risk Patients who represent a potential risk of cCJD infection (have an identified risk factor) |
Additional precautions required | Standard precautions |
|
Background-risk The general population who have no identified increased risk of cCJD infection |
Standard precautions | Standard precautions |