Biomedical Engineering Reference
In-Depth Information
peroxide never exceeded 0.02 ppm. After fumigation no contamination was
observed. They also found that this fumigant did not appear to be corrosive or
damaging to surface materials.
In a before-after intervention study, Boyce et al. assessed the effectiveness of
HPV in the control of C. difficile [ 30 ]. During the intervention period, rooms
that had previously housed C. difficile patients were fumigated. Each room took
approximately 3-4 h to disinfect. The average incidence rates of C. difficile infec-
tion dropped from 2.28 per 1,000 patient days during the pre-intervention phase
to 1.28 (p ¼ 0.047) during the intervention phase.
Burton et al., explored the efficacy of chlorine dioxide in destroying bacteria and
mold in a private home [ 57 ]. Mold was present on the first, second and third floor of
a residence. During the treatment process, concentrations were monitored outside
and on each floor. The house was enclosed in a plastic tent, and the treatment
process did not start until a minimum concentration inside the house reached
500 ppm. The highest concentration in the house was 902 ppm. A variety of
microbial air sampling methods were used, including an Andersen N-6 single
stage sample, spore traps, fungal PCR, and endotoxin samples. In addition, sticky
tape was used to measure total surface fungi. A laboratory evaluation was also
conducted using a challenge test sample of 10 6 fungal spores/ml. The laboratory
evaluation was conducted inside a plastic chamber. The test was performed using
three time periods (4, 8, and 12 h) at 760 ppm. While the fumigant proved to be
effective in destroying viable microorganism in the field tests (kill rates of vegeta-
tive organisms and spores ranging from 84.9 to 97.6 %), researchers found an
increase in endotoxins or mycotoxin levels. When they repeated their experiments
in a laboratory setting, they obtained similar but slightly lower efficacies.
One possible reason for the decrease in kill rate was that the temperature and RH
in the laboratory was lower than in the field study. Temperature and RH are critical
factors in microbial viability.
Clark et al., used a Dyna-Fog model to dispense superoxidized water fog to kill
MRSA and Acinetobacter baumannii organisms [ 58 ]. The superoxide fog solution
was marketed under the trade name of Sterilox. In this study, ceramic tiles were
treated with 10 9 concentrations of the organisms and allowed to dry. The Sterilox
fumigant was released into a laboratory using a 3.8 L fogging machine that created
an airborne concentration of 180 ppm of free chlorine at a pH of 5.2. The fog was
released for 10 min at a maximum setting of 19 L/min. An hour later, the samples
were removed for testing. The MRSA strains showed approximately a 10 4 - fold
reduction and the Acinetobacter strain showed a greater reduction (approximately
10 6 - fold). No information was provided on the effects of this product on surfaces
or equipment.
Other approaches were not as successful. For example, Berrington and Pedler
found that ozone killed microorganisms only in the immediate vicinity of the
generator. At greater distances, ozone was deemed to be ineffective in its ability
to kill MRSA [ 56 ]. There are a number of challenges associated with the use of
ozone, including the need for high relative humidity (RH) to be effective.
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