was 1.4 for the acquisition of either VRE or MRSA
(p<0.05) if the prior room occupant had these
pathogens, “These excess risks accounted for
5.1 percent of all incident MRSA cases and 6.8
percent of all incident VRE cases, with a population
attributable risk among exposed patients of less
than 2 percent for either organism.”
So, the environment, even though a significant
risk factor for acquiring MRSA or VRE, made up
less than 2 percent of the total cases, suggesting
that focusing on the environment to squeeze out
these infections may not yield a lot of juice.
Whole genome sequencing, which gained
prominence years after the Huang article, have
borne out her conclusion. Studies from the UK
showed 45 percent of the strains were not closely
related to any other strains in the multi-hospital,
multi-year study. When the data set the parameters
even more narrowly, suggesting a need for both a
visit to the same hospital and a close genetic link,
the percent of cases that fell into that category
was 10.3 percent — meaning about 90 percent
of the cases had the environment in the hospital
eliminated as the source of transmission. In
fact, a recent review noted many sources in the
community were linked to later healthcare cases.
Other studies around MRSA found even
less transmission occurring in the hospital.
Two studies, one involving 1,854 patients with
or without MRSA and another involving 398
patients with MRSA bacteremia found rates of
MRSA acquisition linked to the environment in
the first study of 8 percent and in the later study
of transmission of 0 percent, clearly suggesting in
the western hospital environment that the focus of
the environment to reduce HAI infections would
gain little in the way of reduction.
If these findings were limited to MRSA and
C. difficile, then the environment could play a
role in other infections, but one study looking
at ICU clinical cultures revealed that only 8.7
percent belonged to a genomically related clonal
lineage. While clearly other bacteria, specifically
Pseudomonas, has showed strong links to the
environment, these studies identified sources such
as sink drains and potable water that cannot be
eliminated by increased cleaning.
One study did a deep dive to prove that the
patient’s own flora were responsible for their
infections. This study showed that among
patients with central line-associated bloodstream
infections (CLABSI) with mucosal barrier injuries
(MBI) the patients did have genetically identical
bacteria identified in their stool before developing
the infection. Interestingly, the data showed
www.healthcarehygienemagazine.com • march 2020
that organisms like Staphylococcus epidemidis,
normally thought of as skin flora, could be found
in the gut and subsequently cause infections
presumably from the GI system. However, it was
already well established that the patient’s own
biome was most likely to cause the infections,
with the exception of organisms not found on
the CDC’s MBI organism list. Given the genetic
diversity seen in whole genome sequencing (WGS)
studies, we can conclude that the environment
is not the source of the majority of infections
occurring in western healthcare today. So, maybe
in the future, infection preventionists won’t be
known as the “handwashing police” but as the
“bathe your patients” police.
Frank Myers, III, MA, CIC, FAPIC, is director of
infection prevention and clinical epidemiology at
UC San Diego Health.
Kim Delahanty, BSN, PHN, MBA, HCM,
CIC, FAPIC, is infection prevention and control
manager at Medicins Sans Frontieres MSF/Doctors
Without Borders.
References:
1. Cohen B, Cohen CC, Loyland B, Larson EL. Transmission of
health care-associated infections from roommates and prior room
occupants: a systematic review. Clin Epidemiol 2017;9:297–310
2. Shaughnessy MK et al Evaluation of Hospital Room
Assignment and Acquisition of Clostridium difficile Infection
INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY MARCH
2011, VOL. 32, NO. 3
3. Drees M et al. Prior Environmental Contamination
Increases the Risk of Acquisition of Vancomycin-Resistant
Enterococci CID 2008:46 (1 March)
4. Huang S et al. Risk of Acquiring Antibiotic-Resistant
Bacteria From Prior Room Occupants ARCH INTERN MED/VOL
166, OCT 9, 2006
5. Eyre DW et al. Diverse Sources of C. difficile Infection
Identified on Whole-Genome Sequencing NEJM September 26,
2013 vol. 369 no. 13
6. Turner NA, Smith BA, Lewis SS (2019) Novel and emerging
sources of Clostridioides difficile infection. PLoS Pathog 15(12):
e1008125. https://doi.org/10.1371/journal.ppat.1008125
7. Price JR Transmission of Staphylococcus aureus between
health-care workers, the environment, and patients in an
intensive care unit: a longitudinal cohort study based on
whole-genome sequencing The Lancet Infectious Diseases
VOLUME 17, ISSUE 2, P207-214, FEBRUARY 01, 2017
8. Long SW, Beres SB, Olsen RJ, Musser JM. 2014. Absence
of patient-to-patient intrahospital transmission of Staphylococcus
aureus as determined by whole-genome sequencing. mBio
5(5):e01692-14. doi:10.1128/mBio.01692-14
9. Roach DJ, Burton JN, Lee C, Stackhouse B, Butler-Wu SM,
et al. A Year of Infection in the Intensive Care Unit: Prospective
Whole Genome Sequencing of Bacterial Clinical Isolates Reveals
Cryptic Transmissions and Novel Microbiota. PLOS Genetics
13(4): e1006724. July 2015
10. Tamburini, FB Precision Identification of Diverse
Bloodstream Pathogens in the Gut Microbiome Nat Med. 2018
Dec; 24(12): 1809–1814 Nature Medicine
Given the
genetic
diversity seen
in Whole
Genome
Sequencing
(WGS)
studies we
can conclude
that the
environment
is not the
source of
the majority
of infections
occurring
in western
healthcare
today.
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