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
(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.