Healthcare Hygiene magazine January 2020 | Page 20

The multiple
environmental
surfaces in indoor
environments are
not independent
but are linked by
hands through
human touching
behaviors, thus
constructing a
surface touch
network.”
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means a contact between the two connected
surfaces. Since the healthcare worker (HCW)’s
routine round behaviors only occurred at special
time points, the HCW’s hand are not included in
the network analysis. To analyze the surface touch
network, we calculated the distances between
surfaces and centrality measures (including the
degree, betweenness and closeness centralities)
of surfaces. The distance, defined as the number
of edges in the shortest path connecting two
surfaces, indicates how fast contaminants diffuse
across multiple surfaces.”
The researchers tested two intervention
methods on bedding surfaces, bedside table
surfaces, as well as public surfaces in the ward,
and assumed a baseline scenario where surface
cleaning was not performed. They hypothesized
several improved scenarios for the two intervention
methods: with 1,000 ppm sodium hypochlorite,
surface cleaning could yield a 0.70 to 1.65 log10
reduction of MRSA on surfaces; with the use of
inefficacious disinfectants or incorrect surface
cleaning methods, the reduction could be low,
such as 25 percent.
The researchers found that, with enough
touching behaviors, the MRSA concentration on
surfaces presented a stable daily cycle, due to
a balance between the MRSA generation and
removal mechanisms (including hand hygiene
and MRSA inactivation on surfaces). They say
the difference in surface touching frequencies
at night and in the daytime makes the MRSA
concentration vary with time rather than maintain
an equilibrium.
“The source bedding surfaces exhibited a differ-
ent MRSA concentration pattern,” the researchers
report. “Since the transfer rate from hands to
porous surfaces was much larger than that from
porous surfaces to hands, MRSA concentration on
the source bedding surface followed the frequency
of touching behaviors and was quite high in the
daytime and decreased at night. Further, at night,
the gain of MRSA to bedding surfaces was lower
than the inactivation, so the MRSA concentrations
on the source bedding surfaces decreased … we
can infer that the optimal cleaning time for the
source bedside table surfaces and hands and
skins was the end of the night, while that for
other surfaces was the beginning of the night.”
They continue, “Comparing different surfaces
of the same patient, we found that the MRSA
concentrations on bedding surfaces were always
the highest, which could be explained by three
reasons. First, the transfer rate of MRSA from
hands to porous surfaces was much higher than
that from porous surfaces to hands, which led
to a net gain of MRSA at most cases on porous
surfaces during the contact. Second, the bedding
surfaces were touched at a higher frequency (6/
hour in the daytime and 3/hour at night) than
bedside table surfaces (2/hour in the daytime
and 0/hour at night), which means the net
transmission from hands to bedding surfaces
occurred relatively frequently. Third, the MRSA
inactivation rate on the porous surfaces (0.0379/
hour) is low relative to that on the skin (0.2112/
hour), so MRSA could survive for a longer period
on the bedding surfaces.”
Comparing surfaces of different patients, Xiao,
et al. (2019) found that those of the index and
the adjacent patients had much higher MRSA
concentrations than those of normal patients:
“Since surfaces of the index patients are sources,
the MRSA concentrations on them must be higher
than other surfaces to maintain a concentration
gradient for the MRSA diffusion. The high MRSA
concentration on surfaces of the adjacent patients
was caused by HCWs’ routine rounds. During
the routine rounds, HCWs directly contacted
patients in a fixed sequence. After visiting the
index patient, the HCW’s hands carried MRSA, of
a high concentration but a limited amount due to
the small area of hands. Then, most of the MRSA
on the HCW’s hands were transmitted to the
surfaces of the adjacent patient and led to more
MRSA of the surfaces of the adjacent patient than
on surfaces of normal patients.” The researchers
conclude that although the MRSA concentrations
on different groups of surfaces varied with the
transfer rates, inactivation rates and touching
frequencies, surfaces of the source patient always
had the highest MRSA concentration while those
of the normal patients are the lowest.
Not surprisingly, the researchers found that
public surfaces had higher MRSA concentrations
than surfaces of the non-index patients, which
might be explained by the distance of the surface
touch network, in that the distance from the
source to surfaces around the non-index patients
was 2 (hands) or 3 (bedding, bedside table and
exposed skin surfaces), while the distance from
the source to the public surfaces was 1. They
explain, “This is consistent with graph theory,
in that surfaces separated by longer distances
have less communication, and thus less transport
of MRSA.”
They also found that public surfaces were very
influential in the entire transmission process, and
that the disruption of these key surfaces had a
greater impact on the topology of the network
than others, indicating that intervention methods
on the public surfaces could be more effective than
interventions on other surfaces. Public surfaces
also lay on all the paths between the surfaces
of the index patient and those of others in the
network. As the researchers note, “Without
these public surfaces, it would be very difficult
for MRSA to spread from the index patient to
other patients via the fomite route. With respect
to closeness centralities, the public surfaces had
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