Healthcare Hygiene magazine January 2020 | Page 27

The researchers
found that floors
in patient rooms
were often
contaminated with
MRSA, VRE and
C. difficile.
100
Of
occupied rooms
surveyed,
41 %
had one or more
high-touch
objects in contact
with the floor.
two sub-types of fomite-mediated transmission:
direct fomite (e.g., shedding onto fomites) and
hand-fomite (e.g., shedding onto hands and
then contacting fomites). They used this model
to examine influenza, rhinovirus and norovirus in
four venue types.
As the researchers explain, “Transmission ven-
ues are complex environments characterized both
by their physical properties (types and quantity of
fomites) and by the nature of host behaviors within
these spaces (frequency of contact with fomites,
the duration of time spent in a venue, or the
density of hosts within the venue). Furthermore,
risk within a venue may also vary by age group
based on not only differences in contact rates but
also shedding rates.”
For their analysis, the researchers used a
simplified representation of a venue, based on
three factors: the proportion of contamina-
tion-accessible fomites, shedding rates, and how
frequently individuals interact with those fomites.
For this analysis, the researchers treated each
venue as a closed system and did not consider
host movement. They included control measures
parameters (cleaning rate and the proportion of
pathogens killed by decontamination) to contrast
the effectiveness of control measures among the
pathogens and across venues. They considered
three frequencies for all three venues: 1/2 days,
daily, and twice daily.
The researchers considered two behavioral
parameters: the rate of self-innoculation
(face-touching events) and the rate of fomite
touching. They found that for all pathogens,
the inactivation rates on fomites were highly
variable by surface, with higher inactivation
rates on hands (which are a porous surface):
“Influenza, the only pathogen for which decay
rates were available for porous environmental
surfaces besides stainless steel, had much higher
inactivation rates on porous surfaces. Notably,
some pathogens exhibited biphasic inactivation,
with faster initial inactivation followed by a period
of slow inactivation or persistence without mea-
surable decay. When this occurred, we used the
average inactivation estimates over the first hour,
when decay rates were highest, to parameterize
our model. Influenza appears to survive for the
shortest amount of time on hands, with an order
of magnitude higher inactivation rate than either
rhinovirus or norovirus. While inactivation rates on
fomites were relatively insensitive to temperature,
they were more sensitive to changes in humidity,
with drier conditions generally promoting higher
inactivation rates. The exception was influenza,
which appeared to survive better at low humidity.”
The researchers discovered that influenza trans-
fers more readily from fomites to hands than hands
www.healthcarehygienemagazine.com • january 2020
to fomites, while the reverse appears to be true
for norovirus. For influenza, transfer efficiency was
also lower for porous than non-porous surfaces.
Shedding concentrations varied considerably
between pathogens as well as between individuals
for a given pathogen, the researchers reported.
The average shedding rate for influenza was
found to be an order of magnitude higher than
for rhinovirus and norovirus.
Behavior and venue are important drivers of
transmission, Kraay, et al. (2018) emphasize. For
influenza, transmission via the fomite route is only
sustainable for venues with high touching rates,
they say: “Airborne transmission may therefore
be more likely to sustain influenza transmission
in venues where either the touching rate is low
(offices) or proportion of accessible surfaces is
very low (outdoor venues). By contrast, our model
suggests that rhinovirus and norovirus transmission
by the fomite pathway are sustainable in nearly
all venues. While norovirus and rhinovirus shed
fewer viral copies than influenza, they have
much longer infectious periods, as well as longer
persistence on hands.”
The direct fomite route is most important
for transmission of influenza, the researchers
found, whereas the hand-fomite route was more
important for rhinovirus and norovirus: “Based
on our sensitivity analyses, for norovirus and
influenza, the relative importance of each pathway
was highly sensitive to the fraction of pathogens
shed onto hands rather than surfaces. When a
larger proportion of pathogens was shed onto
surfaces, the direct fomite route became more
important. The reason the hand-fomite route
dominated for rhinovirus is due to its relatively
larger transfer efficiency proportion and low
inactivation rate on hands.”
For influenza, only higher frequency (≥ 1/
day) surface decontamination strategies appear
to meaningfully reducing transmission, with a
maximum reduction of 40 percent in low sur-
face-contact venues. However, fomite transmission
is only possible in settings with higher touching
rates and proportions of accessible surfaces.
Thus, surface decontamination for influenza may
prevent outbreaks in venues with moderate surface
contact rates and many accessible surfaces, the
researchers say. In contrast, in the researchers’
simulations similar interventions for rhinovirus and
norovirus were not effective, even with cleaning
frequencies of up to twice per day.
The researchers indicate that it may be
important to tailor environmental interventions
to specific venues, “as the effect of a given
influenza transmission mechanism may not be
consistent between venues with different envi-
ronmental properties … To be effective, surface
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