Healthcare Hygiene magazine October 2019 | Page 24

is useful for monitoring the effectiveness of cleaning and
disinfection practices.
The aim of the study by Casini, et al. (2018) was to
evaluate cleaning procedure efficacy in reducing bacterial
contamination. The researchers analyzed surface contamina-
tion using cultural methods and ATP detection, performed
with a high-sensitivity luminometer. The values 100 CFU/cm2
and 40 RLU/cm2 were considered as the threshold values
for medium-risk category areas, while 250 CFU/cm2 and
50 RLU/cm2 were defined for the low-risk category ones.
The cleaning/disinfection procedure reduced the medium
bacterial counts from 32±56 CFU/cm2 to 2±3 CFU/cm2 in
the low-risk area and from 25±40 CFU/cm2 to 7±11 CFU/
cm2 in the medium-risk one. Sample numbers exceeding the
threshold values decreased from 3 percent and 13 percent
to 1 percent and 5 percent, respectively. RLU values also
showed a reduction in the samples above the thresholds
from 76 percent to 13 percent in the low-risk area.
As Casini, et al. (2018) explain, “Our results cannot
be considered as indicators of microbial contamination,
considering also that ATP molecules present on surfaces
may not have a microbial origin. Currently, ACCs of < 2.5–5
CFU per cm2 on hand-touch sites have been assigned as a
microbiological limit. An additional international institution
also uses microbiological standards incorporating the pres-
ence of indicator organisms. Their identification depends
on the risk to human health and on the matrix inspected.”
The researchers point to the variability of ATP system
benchmarks depending on the type of luminometer used.
These range from 25 RLUs to 500 RLUs for 10–100 cm2 on
hospital surfaces. They note: “A poor correlation between
microbial contamination and RLU values has been demon-
strated, where the values of the former are low. For this
reason, the relationship between the two indices considered
is not evident. Different values should be chosen, depending
on patient risk; surfaces in outpatient clinics are not neces-
sarily as critical for infection risk as sites beside a ventilated
patient receiving intensive care. ATP can also be confounded
by disinfectants, microfiber products, and manufactured
plastics used in cleaning and laundering industries. If an
ATP assessment was introduced into hospitals, it should
help to monitor cleaning quality and its failures, even when
there is not a serious risk for patients. In conclusion, since
a visual assessment does not offer reliable information on
infection risk to patients, high-risk (hand-touch) surfaces
in hospitals should be subjected to a scientific screening
method to monitor the overall levels of microbial dirt. If
they were integrated into a formal monitoring regimen,
ATP and/or microbiological benchmarks would help to
identify unacceptable soil levels and associated patient risk
provided they were systematically collected over time and
interpreted accurately.”
In their review, Nante, et al. (2017) found that the country
where the studies were conducted may have influenced
the choice of the RLU cutoff values: “For example, in the
U.S. the most often used value corresponded to 500 RLU
…These differences among the benchmark values make
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difficult the comparisons between measurements carried out
with different tools … Another limitation of this technique
could be the residues of detergent or disinfectants on the
surfaces, which may require rinsing of these surfaces before
the use. Despite of these considerations, some advantages
of this technique can be listed, such as the possibility to
provide real-time results (within 20 seconds of sampling),
its simplicity of use (which makes possible the adoption of
the method not only by trained healthcare staff), and the
quantitative results. The latter allows comparisons between
pre- and post-cleaning or between different surfaces. In
conclusion, the ATP bioluminescence could be considered
a practical, useful method to assess hospital hygiene, per-
forming better than visual inspection, if properly adopted,
also being aware of its possible limits.”
The variability, despite the benefits of a monitoring
method such as ATP, is a significant concern. Chai, et al.
(2018) observe that, “The lack of environmental sampling
standardization in healthcare hinders the ability to objectively
assess and compare the quality of articles evaluating the
efficacy of newer antimicrobial technologies. This variability
needs to be addressed by regulatory agencies. The many
variables in each of the four process steps (collection, trans-
port, recovery and culture) can independently influence the
quality of the sampling methods and inter-study comparisons
are thus admittedly difficult. It is tempting to suggest a
limited number of environmental sampling methods to
facilitate standardization. Unfortunately, this is a challenge
specifically because the selection of each method within
the four process steps depends upon the surface, its size,
shape, and location, and the results desired (qualitative
versus quantitative).”
The researchers add, “At a minimum, a description of
methodology should consider these elements: 1) moisture
must be present at the time of sampling, 2) a neutralizing
solution is necessary to arrest residual disinfectant action,
3) a physical dissociation method must be used to release
organisms from the collection device prior to culturing, and
4) special consideration is required for the collection and
culturing of spore-forming organisms.”
Rawlinson, et al. (2019) acknowledge that evidence on
how best to sample these surfaces “is patchy and there
is no guidance or legislation in place on how to do this.”
Their review assessed current literature on surface sampling
methodologies, including the devices used, processing
methods, the environmental and biological factors that
might influence results. The researchers emphasize that,
“Although the numbers of cells or virions recovered from
hospital surface environments were generally low, most
surfaces sampled were microbiologically contaminated. Of
the organisms detected, multi-drug resistant organisms and
clinically significant pathogens were frequently isolated and
could, therefore, present a risk to vulnerable patients. Great
variation was found between methods and the available data
was incomplete and incomparable.” They add, “In light of
the changing awareness of the risk the surface environment
poses, more hospitals are considering instigating routine
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