An Overview of the Options for Antimicrobial Hard Surfaces in Hospitals - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 137

7.1 Role of the Environment in Transmission
7.1.1 Evidence That Contaminated Surfaces
Contribute to Transmission
The contaminated environment has historically been considered to play a negligible
role in the transmission of most hospital pathogens [ 1 , 2 ]. However, the healthcare
environment has been shown to become contaminated with multidrug-resistant
organisms (MDROs) such as methicillin-resistant Staphylococcus aureus
(MRSA), Clostridium difficile and some resistant Gram-negative rods (R-GNR)
including Acinetobacter baumannii [ 3 - 6 ]. Transmission routes of pathogens are
complicated and difficult to investigate so studies focused on the role of surfaces
in transmission have been rare until relatively recently [ 2 ]. Data suggesting
that contaminated surfaces play an important role in transmission come from
studies modeling transmission [ 7 - 9 ], microbiological studies in vitro and in situ
[ 3 , 10 - 12 ], observational epidemiological studies [ 13 - 18 ], intervention studies
aimed at improving the efficacy of cleaning and disinfection [ 5 , 19 - 24 ] and
outbreak reports [ 25 - 27 ].
Recent epidemiological evidence suggests that patients admitted to rooms
previously occupied by a patient with environmentally-associated pathogens
increases the chances of acquiring the same pathogen [ 14 - 16 , 28 ]. The most likely
explanation is residual contamination from the prior room occupant. The epide-
miological association is strengthened by the finding that improving terminal
disinfection mitigates the increased risk from the prior room occupant [ 19 , 21 ].
7.1.2 The Relationship Between Contamination
Burden and Transmission Risk
The relationship between the level of surface contamination and the risk of transmis-
sion has not been studied in detail. It depends on various factors, including the
characteristics of the organism involved, patient susceptibility, and staff compliance
with infection control policies (for example hand hygiene following contact with
environmental surfaces) [ 11 , 29 , 30 ]. A number of studies have identified a correla-
tion between a quantitative or semi-quantitative measure of the level of environ-
mental contamination and the risk of pathogen acquisition (Fig. 7.1 )[ 25 , 31 , 32 ].
However, since none of these studies demonstrate that an intervention to reduce the
level of contamination reduces the risk of transmission, the correlation could be
explained by the fact that patients who are already infected or colonized shed
more contamination into the environment, which is plausible. Whilst one of the
three studies (Salgado et al.) did evaluate an intervention, the data correlating
contamination burden with HAI was not stratified by the intervention, which would
have been one way to assess likely causation [ 31 ].