The Role of Contaminated Surfaces in the Transmission of Nosocomial Pathogens - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 31

the particular environment, and whether there is an ongoing outbreak at the time
of sampling. Methodological differences in sample collection and culture make
comparisons between studies difficult and in some cases the true level of environ-
mental contamination may be underestimated.
Patients are the prime source of contamination, so surfaces in the vicinity of
patients that are touched frequently by healthcare workers and patients, termed
“high-touch surfaces”, have a higher frequency of contamination than other sites
[ 16 , 22 , 29 , 30 ]. For example, a recent study defined high-touch surfaces as the bed
rails, the bed surface and the supply cart, based on their observed frequency of contact
[ 29 ]. Developing an understanding of which sites are more likely to be contaminated
with pathogens can guide infection control practice and direct new innovations.
Areas around patients are frequently contaminated with MRSA, VRE and
C. difficile [ 17 , 31 , 32 ]. The frequency of MRSA and VRE contamination correlates
with the number of culture positive body sites [ 16 , 18 , 33 ]. Infected patients
shed more pathogens than those who are only colonized, and diarrhea results in
widespread contamination [ 16 , 34 , 35 ].
Contamination of rooms of unaffected patients has been reported for C. difficile ,
MRSA and VRE. C. difficile was identified on 16-17 % of samples from the rooms
of patients without known C. difficile infection (CDI) [ 14 , 36 ], MRSA was cultured
from 43 % of beds used by patients not known to be MRSA positive [ 17 ] and VRE
was cultured from 13 % of surfaces in the rooms of patients with unknown VRE
status [ 37 ]. Contamination of rooms of unaffected patients is most likely to be due
to continued viability of organisms shed by previous occupants [ 12 , 17 , 38 , 39 ]
but may also result from importation by HCPs or visitors, or shedding from
asymptomatic carriers [ 40 , 41 ].
Relatively few prospective studies have evaluated surfaces contamination with
Gram-negative or norovirus. The frequency of contamination is approximately
5-10 % of surfaces for Gram-negative bacteria [ 20 , 21 , 42 - 44 ] and was found to
be highly variable, although usually less than 20 % of surfaces for norovirus
RNA [ 45 , 46 ].
Highly variable levels of contamination have been reported during outbreaks.
Frequent environmental contamination has been identified and implicated as a
contributory factor during continuing outbreaks of C. difficile , MRSA, VRE,
A. baumannii and norovirus [ 35 , 47 - 50 ].
Contamination of air has been reported but the interchange between contami-
nated air and surfaces is not well defined [ 25 , 26 , 51 - 53 ].
3.3 The Concentration of Contamination Is Sufficient
for Transmission
In general, colonized or infected patients have a higher concentration of contami-
nation than their surrounding surfaces [ 18 , 30 , 54 , 55 ]. The concentration of VRE
on patients' skin is approximately 10 3 colony forming units (CFU) per 50 cm 2 [ 56 ]