Abstract
Introduction. The aim of this study was to evaluate the efficacy
of ClO2 with regard to viruses which show a particular resistance
to oxidizing agent such as HAV and Norwalk and Norwalk-like
viruses, and which play an important role in the epidemiology of
viral foodborne diseases.
In the food industry, disinfection of processing systems and equipment
is a very important instrument to prevent secondary contamination
and to guarantee food safety. Among disinfectants,
chlorine dioxide (ClO2) presents a good efficacy at wide range
of pH values, its action is rapid and generates few reaction byproducts
if compared to hypoclorite. Experimental studies have
highlighted that ClO2 shows a good bactericidal activity and it is
also active towards viruses. Furthermore, the low concentrations
and low contact times required to obtain microbial load reduction
are favourable elements for the application of this compound in
the industrial sanitizing practices.
Methods. As it is impossible to cultivate the Norwalk virus in vitro,
we tested the resistance of Feline calicivirus (F9 strain) vs. ClO2, in
comparison with HAV (strain HM-175) and CoxsackieB5. Chlorine
dioxide was used at concentrations ranging from 0.2 to 0.8 mg/l in
water solution, at pH 7 and at +20 °C. Viral suspensions were added
to disinfecting solution and, at pre-set times, were sampled to undergo
to titration after blocking the disinfectant action with thiosulphate 0.05
M. On the basis of the data obtained, for each virus and in relation
to different concentrations, mean reduction times were calculated for
99%, 99.9% and 99.99% using the regression analysis model.
Results. As regards Feline calicivirus, at a concentration of 0.8
mg/l of ClO2, we obtained the complete elimination of the viral
titre in 2 min while 30 min were required at concentrations of 0.2
mg/l. Coxackie B5 showed a similar behaviour, being completely
inactivated in 4 min with 0.4 mg/l of ClO2 and after 30 min at a
concentration of 0.2 mg/l. Inactivation was quicker for HAV, which
was eliminated after only 30 sec at a concentration of 0.8 mg/l and
after 5 min at 0.4 mg/l.
Conclusion. Our data show that for complete inactivation of HAV
and Feline calicivirus, concentrations ? 0.6 mg/l are required.
This observation is true for Coxsackie B5 too, but this virus has
shown a good sensitivity at all concentration tested according to
regression analysis results. For Feline calicivirus and HAV, at
low concentrations of disinfectant, prolonged contact times were
needed to obtain a 99.99% reduction of viral titres (about 16 and
20 minutes respectively).
