Healthcare Hygiene magazine October 2019 | Page 21

wholly unreliable in the measure of surface contamination.
ATP and ACC were recommended as effective measures with
benchmarks of <100 RLU and <2.5 CFU/cm 2 , respectively.
This review found that in the healthcare industry as well,
cleaning effectiveness has largely gone unmeasured and
is maintained by subjective evaluations. Researchers also
found that in every study completed to measure cleaning
effectiveness using these methods with various benchmarks,
current cleaning practices left surfaces organically and
microbiologically contaminated.”
“’Clean’ is usually defined as the removal of dirt or
unwanted matter,” says Charles P. Gerba, PhD, professor of
microbiology and environmental sciences at the University
of Arizona. “I prefer ‘hygienic’ since the goal is to reduce
the transmission of infectious microorganisms. I believe this
can be done with the application of quantitative microbial
risk assessment. I think the healthcare area is in need of
standards; they are used to control the spread of infectious
microorganisms in water and food – and it is time we apply
these same concepts to disinfection and cleaning – other-
wise we have no scientific way to judge effectiveness of
different interventions.”
Gerba says he is in favor of using the CFU standard
“because you need a certain level of bacteria to have a high
probability of infection.” He adds, “ATP may also be useful
to judge or compare interventions – but both have limits.”
The difficulties in measuring cleaning efficacy
are compounded by the lack of standardized
methodologies and are rarely quantitative.
Gerba says a definitive microbial standard for surface
cleanliness is feasible, explaining, “Application of quantitative
microbial risk assessment with knowledge of the number of
pathogenic organisms on a surface and then modeling the
transmission can give number(s) for guidance.”
He points to a study on which he was a co-author a
few years ago where it was concluded that a reduction in
bacterial numbers on a fomite by 99 percent (2 logs) most
often will reduce the risk of infection from a single contact
to less than 1 in 1 million. This quantitative microbial risk
assessment (QMRA) by Ryan, et al. (2014) included a problem
formulation for fomites and hazard identification for seven
microorganisms, including pathogenic Escherichia coli and
E coli 0157:H7, Listeria monocytogenes, norovirus, Pseu-
domonas spp, Salmonella spp, and Staphylococcus aureus.
The goal was to address a risk-based process for choosing
the log10 reduction recommendations, in contrast to the
current Environmental Protection Agency (EPA) requirements.
For each microbe evaluated, the QMRA model by Ryan, et
al. (2014) included specific dose-response models, occurrence
determination of aerobic bacteria and specific organisms
on fomites, exposure assessment, risk characterization, and
risk reduction. Risk estimates were determined for a simple
www.healthcarehygienemagazine.com • october 2019
scenario using a single touch of a contaminated surface and
self-inoculation. A comparative analysis of log10 reductions,
as suggested by the EPA, and the risks based on this QMRA
approach was also undertaken.
The researchers found that aerobic bacteria were the
most commonly studied on fomites, averaging 100 CFU/
cm2. Pseudomonas aeruginosa was found at a level of 3.3
× 10−1 CFU/cm 2 ; methicillin-resistant S. aureus (MRSA),
at 6.4 × 10−1 CFU/cm 2 . Risk estimates per contact event
ranged from a high of 10−3 for norovirus to a low of 10−9
for S aureus.
“A standard based on quantitative microbial risk assess-
ment makes sense,” Gerba confirms. “It is used in both
the water and food industries to set minimum treatment
requirements. For example, treatment of drinking water to
transmission of infectious waterborne organisms is set for
a one day/one-time event risk of 1:1,000,000.”
The History of the Quest for a Standard
As we have seen, one of the first to question the con-
cept of “clean,” years ago, Dancer (2004) noted that “…
the importance of a clean environment is likely to remain
speculative unless it becomes an evidence-based science.”
She had called for microbiological standards with which
to assess clinical surface hygiene in hospitals, based on those
used by the food industry. She had mused that a standard
would require identifying a specific ‘indicator’ organism, the
presence of which would suggest a requirement for increased
cleaning. For example, indicators would include Staphy-
lococcus aureus, including methicillin-resistant S. aureus,
Clostridium difficile, vancomycin-resistant enterococci and
various Gram-negative bacilli.
The standard would also indicate a quantitative aerobic
colony count of <5 CFU/cm 2 on frequent hand-touch surfaces
in hospitals, explaining that, “The principle relates to modern
risk management systems such as HACCP, and reflects the
fact that pathogens of concern are widespread. Further
work is required to evaluate and refine these standards and
define the infection risk from the hospital environment.”
Before the role of the environment had gained great ac-
ceptance, Dancer (2004) had asserted, “Hospital patients can
acquire organisms from many sources, including the environ-
ment, but the extent to which the latter contributes toward
HAI is largely unknown. This is because cleaning has never
been regarded, let alone investigated, as an evidence-based
science. The difficulties in measuring cleaning efficacy are
compounded by the lack of standardized methodologies
and are rarely quantitative. Environmental screening usually
takes place on an ad hoc basis after an outbreak, but it is
patently impossible to screen the entire surface of a ward and
finding the outbreak strain is not guaranteed. Furthermore,
organisms still must be transmitted to patients. As this is
thought to occur via staff hands, strategies for controlling
HAI are more likely to favor improvements in hand hygiene
than comprehensive screening programs. Cost-benefit and
lack of standardized methodologies might also explain
the perceived reluctance of private cleaning companies to
participate in screening. Certainly, most microbiologists
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