Survival of Microorganisms on Inanimate Surfaces - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 10

Table 2.1 Infectious doses for selected pathogens
Infectious
dose Organisms Reference

(1)-10-100
viable
particles

Norovirus, Rotavirus, EHEC,
ETEC, C. difficile , Enterococci
incl. VRE

Ward et al. [ 122 ], Paton and Paton [ 88 ], Pang
et al. [ 85 ], Lawley et al. [ 68 ], Porter
et al. [ 92 ], Yezli and Otter [ 130 ], Robine
et al. [ 97 ]

1 viable
particle
in water

Oocysts of cryptosporidia Chappell et al. [ 17 ]

10 5 viable
particles

Salmonella enteritidis Craven et al. [ 24 ]

>

there is a risk of transmission (Table 2.1 ). In immuno-compromised patients, the
required numbers of microorganisms for causing infectious diseases is even lower,
increasing the risk of HAI in these populations. Inanimate surfaces have been described
as source for HAI-outbreaks. Hayden et al. [ 49 ] demonstrated that touching the
environment contaminated with relatively low pathogen concentrations in a room
occupied by a patient colonized with VRE is associated with approximately the same
risk of VRE acquisition on hands as touching an affected patient directly. Evidence of
the importance of environmental transmission is further provided by studies showing an
increased risk of infection in patients admitted to the same rooms previously occupied
by other infected/colonised cases. This has been shown for C. difficile [ 101 ], VRE and
MRSA ([ 54 , 55 ], and also own observations). Environmental Norovirus contamination
has been repeatedly found to be correlated with continuing outbreaks [ 128 ], although
the significance of this pathway has not been fully elucidated.
The importance of surface contamination is also shown by reduction in the rate of
HAI when effective measures of environmental disinfection are implemented [ 50 , 10 ,
26 ]. A recent observational study showed a significant reduction in C. difficile
infection rates following the introduction of sporicidal wipes in an environmental
cleaning regimen in an acute London trust [ 16 ]. However, not all studies have shown
a direct link between surface disinfection and reduction in infection rates, probably
because of the complex interactions and transmission routes in the clinical practice.
Yet, in summary it is undisputed that contaminated surfaces may contribute to
the transmission of pathogens and may thus pose a critical element in the chain of
transmission of microorganisms [ 41 ].

2.3 Persistence of Microorganisms on Inanimate Surfaces

The risk for transmission of HAI depends of the persistence of nosocomial
pathogens on surfaces. The longer a microorganism may persist on a surface, the
longer the contaminated surface may be a source of transmission and thus endanger
a susceptible patient or healthcare worker of becoming the target of infection.
In order to estimate the risk of cross contamination, Kramer et al. [ 64 , 65 ]
have published a systematic review on persistence of pathogens on surfaces.