An Overview of the Options for Antimicrobial Hard Surfaces in Hospitals - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 140

pathogens from surfaces whereas enhanced conventional disinfection is associated
with a reduction but not elimination of pathogens [ 3 , 33 ], it seems likely that the
improved environmental reduction achieved by HPV explains the improved clinical
outcomes due to a greater reduction on the environmental burden. However, further
studies are necessary to confirm this point.
There is in vitro evidence that the extent to which transmission is interrupted is
proportional to the level of surface contamination. Lawley et al. used an in vitro
mouse model to show that the degree to which transmission of C. difficile was
blocked correlated with the log-reduction of the various disinfectants tested [ 8 ].
Despite the evidence that there is a causal relationship between the concentration
of contamination and the risk of transmission, the level of contamination on a
surface that is a risk for onward transmission is not known. The degree of shedding
and the infective dose can be used to guide the appropriate target for hospital
cleaning and disinfection. Certain pathogens such as C. difficile and norovirus
can be shed into the environment in high numbers and have a low infectious dose
[ 2 , 34 , 35 ]. For example, stool concentrations of norovirus can reach more than
1 10 12 particles per gram [ 2 ] and up to 10 5 virus norovirus particles per 30 cm 2

have been identified on hospital surfaces [ 36 ], whereas the infectious dose is 1-100
particles [ 35 ]. Therefore, the presence of a pathogen on a surface at any concen-
tration may be a risk for transmission. This is reflected in proposed guidelines for
microbiological hygiene standards [ 37 ] and recent discussion surrounding the
intended target for hospital disinfection [ 38 , 39 ]. Dancer [ 37 ] proposed an absence
of specific indicator organisms ( S. aureus , including methicillin-resistant S. aureus ,
C. difficile , VRE and various Gram-negative bacilli), and a quantitative aerobic
colony count of 5 cfu/cm 2 was selected based on its use in some

sectors of the food industry. A lower standard of

5 cfu/cm 2 .The

< <

2.5 cfu/cm 2 has been adopted in
recent years [ 32 , 40 - 42 ]. Whilst it has not been demonstrated that contamination
below this level is 'safe' and above this level is 'unsafe', the number of hygiene
failures has been correlated with the acquisition of pathogens (Fig. 7.1 )[ 32 , 43 ].

<

7.1.3 Potential Role for Antimicrobial Surfaces

A number of different interventions aimed at improving environmental hygiene have
been evaluated. Approaches to improve the efficacy of existing methods include
increased staff training, more hours for cleaning staff, and the use of fluorescent
markers or ATP analysis of surfaces to performance-manage the cleaning process
[ 21 , 22 , 40 , 44 , 45 ]. Novel methods include new disinfectants with superior efficacy,
the advent of 'no-touch' automated room disinfection systems that do not rely of the
operator to assure adequate distribution and contact time of the chemical agent, and
new cleaning materials such as microfiber [ 24 , 33 , 46 ].
Switching from one disinfectant to a product with superior microbio-
logical efficacy in particular has been shown to reduce transmission [ 5 , 20 , 23 ,
24 , 47 , 48 ]. However, one of the problems with available disinfectants is the