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virucidal activity. However, if sporicidal activity is required, a 10 minute

immersion time should be used.

(iii) Peroxygen compounds 'Virkon' is a stable peroxygen disinfectant which is

effective against most vegetative bacteria and viruses, but has proved less

effective than glutaraldehyde against mycobacteria (18,37) and enteroviruses

such as poliovirus (10). Furthermore, some peroxygen compounds affect the

components of endoscopes and automated processing equipment. The Working

Party does not recommend peroxygen disinfectants for gastrointestinal

endoscopy.

(iv) Chlorine dioxide Chlorine dioxide and other chlorine releasing agents have

been used for slime control and treatment of drinking and waste water.

Instrument disinfectants known as 'Tristel', 'Dexit' and 'Medicide' are

commercially available. These products comprise two components, a base and

an activator, requiring addition and dilution in accordance with the manufacturers'

instructions, ie 1 part base, 1 part activator and 8 parts water. Errors in the

preparation are possible although this criticism does not apply to 'Tristel' and

'Medicide' as these are supplied at their use concentrations.

Freshly prepared chlorine dioxide is highly effective and rapidly destroys bacterial

spores, ie B.subtilis and other non-sporing bacteria, including M.tuberculosis,

M.avium intracellulare, other atypical mycobacteria and Pseudomonas

aeruginosa. The spores of B.subtilis are very resistant to disinfectants and, as

such, provide a very discriminatory and stringent test for new disinfectants (19).

Sporicidal activity is maintained for 7 - 14 days provided the disinfectant is stored

in sealed containers with minimal head space above the solution (38). This

requirement will be difficult to attain in many automated washer/disinfectors and

further tests will be necessary to assess stability over a 14 day period. When

used according to the manufacturers' prescribed conditions, sporicidal activity is

substantiated in 10 minutes and bactericidal and virucidal activity in 5 minutes

(the same time as 'Nu Cidex').

Although 'Tristel', 'Dexit' and 'Medicide' are described by the manufacturers as

user safe, strong fumes of chlorine dioxide are given off during preparation and

use. As with other resiratory irritants these cn be substantially reduced if

enclosed and/or exhaust ventilated facilities are used. The fumes are unpleasant

but tests commissioned on behalf of the manufacturers have shown the level of

ClO2 given off to be below the exposure limits set by the HSE in EH40/95. It is

strongly recommended by the Working Party, however, that vapour emissions

are extracted and/or suitably contained.

Chlorine dioxide is also more damaging to instrument and processor components

than glutaraldehyde. As far as is known, none of the leading endoscope

manufacturers has completed compatability tests with instrument components.

Experience with chlorine dioxide has demonstrated discoloration of the black

plastic casing of flexible endoscopes but this change may be only cosmetic. If

chlorine dioxide is used in automated washer disinfectors component contact

times are likely to be much longer and, therefore, damage is even more likely.

Some material compatibility tests have been carried out by Birmingham

University and a summary of this work is available from the disinfectant suppliers.

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