Role of the Microbial Burden in the Acquisition and Control of Healthcare Associated Infections: The Utility of Solid Copper Surfaces - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 64

disinfectants used on environmental surfaces, thus leading to their persistence and
continued distribution within the built environment and presenting a continued risk
of being transferred to a patient, healthcare worker or object within the built
hospital environment [ 100 ].

4.2.2 Transmission of Pathogens to Patients
and Healthcare Workers

Certain factors must be met for a microbe to transition from its role as an inhabitant of
the surfaces associated with the built clinical environment to pathogen that can be
transmitted to a patient or healthcare worker. First, the pathogen must be able to
survive on the objects and surfaces within the environment for a sufficiently long
period of time while retaining its ability to be virulent or its ability to colonize a
susceptible host after its subsequent liberation from the surface and resulting trans-
mission/establishment. Second, contamination of the environment by a particular
pathogen must be sufficiently frequent to account for its loss from the object or
surfaces as a consequence of routine cleaning, desiccation, or starvation. Third, the
agent must be present at a concentration sufficient to establish itself upon encountering
the new host or location. Certain nosocomial pathogens, such as Norovirus, have
incredibly small infectious doses with a median dose of 18 viruses [ 86 ] while the
environmental dose of the causative agent of the majority of CAUTI, Escherichia coli ,
is not as evident. The Infectious Disease Society of America (IDSA) has classified that
in the absence of symptoms a concentration of

10 5 colony forming units (CFU) per

ml coupled where 1 bacterial species is present in the urine of a catheterized patient

that the individual has an asymptomatic catheter associated bacteriuria (CA-ASB)
[ 35 ]. A CAUTI is defined as the “presence of symptoms or signs compatible with
urinary tract infections (UTI) with no other identified source of infection along with

10 3 CFU/mL of

1 bacterial species” from a catheterized or previously catheterized
( 48 h) urine sample [ 35 ]. However the guidelines are silent as to the origin and/or
concentration of the microbe(s) required to establish the CA-ASB or CAUTI. The
concept of infectious dose from the environment as it pertains to nosocomial infection
has not been rigorously studied for the majority of the HAI. Further study is warranted.
Hospitals have put into place measures in an attempt to decrease the contamination
or likelihood of colonization of healthcare workers with infectious pathogens. Focus
has been placed on increased hand hygiene, contact precautions, and enhanced
environmental cleaning. In 2006 Pittet and colleagues presented an evidence-based
model arguing for improved hand hygiene practices during patient care as being the
most important method for preventing HAI and spread of antimicrobial resistant
pathogens [ 61 ]. In their model, five steps are required for the transmission of patho-
gens within the clinical care setting. Collectively, the model considers the microbes
and their transmission from objects, healthcare workers, and patients to the next
individual or object. The first step requires that the microbe be present or resident