Home' Inclean : INCLEAN May-Jun 2015 Contents 46 INCLEAN May/June 2015
The use of ultraviolet disinfection to combat HAIs has expanded
significantly over the past several years. According to manufacturers’
estimates, there are now over 600 portable UV disinfection units
in use in the US and internationally. Their use is supported by a
growing body of research demonstrating the effectiveness of these
systems in disinfecting healthcare surfaces. The results of these studies
are encouraging, though they are not entirely surprising when you
consider that UV has been used successfully for decades for water, air,
and surface disinfection.
Despite this long history, the use of portable UV systems in
healthcare facilities is still relatively new and our understanding
of its effectiveness is evolving. In many ways, a hospital room is a
complicated environment and, because it differs greatly from other
UV applications, it does present some unique challenges. The purpose
of this whitepaper is to provide infection preventionists and other
hospital staff with the latest information about how to most effectively
deploy UV disinfection systems in a healthcare setting.
What happens to UV light in a hospital room?
A typical hospital room is filled with numerous objects- a bed,
furniture, equipment, etc. These objects have complex shapes and
are made up of a variety of different materials, such as plastic,
wood, glass, fabrics, etc. The size and shape of the room as well as
the type and location of the objects in the room all affect how the
UV light gets dispersed, which in turn determines how completely
the room is disinfected.
When light hits a solid object, it can be absorbed, transmitted, or
reflected (Figure 1). For most materials, a combination of these three
phenomena occurs, and it can depend heavily on the wavelength of
the light. In the case of germicidal UV, the vast majority of materials
are strongly absorbing. For example, materials like white plastic, which
reflects visible light and therefore looks bright to our eyes, will typically
absorb greater than 95% of the UV, reflecting very little. This is true
of most of the surfaces you will find in a typical room, including paint,
vinyl wall coverings, or wood. Glass is another common material and
also has interesting properties. While it transmits visible light, which
is why we can see through it, it will strongly absorb short-wavelength
UV. Metal surfaces often reflect UV, but how strongly they reflect
depends on the type of metal and the degree of surface polish.
Because of the prevalence of UV-absorbing materials in a hospital
room, almost all of the light that leaves a UV disinfection lamp will
be absorbed by the first object it hits. This means there is very little
reflected light bouncing around a typical room. Since the laws of
physics tell us that light can only travel in a straight line, all hospital
rooms will have some surfaces that are shadowed, occluded, obscured,
or otherwise do not see the full intensity of UV light from the device.
As a result, the effectiveness of UV disinfection is reduced and
microbes may remain viable on those surfaces, ready to infect another
patient or healthcare worker.
This is a challenge common to all UV disinfection devices,
regardless of the type of light source or the presence of light sensors.
Recent advances in
the UV disinfection of
Below is an excerpt from a paper written by Brian Tande,
PhD highlighting the effectiveness of ultraviolet disinfection
technology in combating healthcare associated infections (HAIs).
Effectiveness data provided by device manufacturers usually includes
log-reduction measurements for test samples placed in direct line of
sight of the device. And, unfortunately, this is the data often used to
determine the cycle time of the device. The actual dose received by a
shadowed or occluded surface can be lower by a factor of a hundred
or even a thousand. Surfaces that are not directly exposed to the
lamp, such as on the back of the headboard or a bed rail, receive
significantly less UV light, often much less than an adequate dose.
Maximizing the effectiveness of UV
While we are restrained by the laws of physics, we can use our
knowledge of it to find ways to dramatically improve UV disinfection
in healthcare environments. We’ll highlight two recent developments
that help healthcare facilities make the most out of their UV devices.
The first is the invention of UV-reflective coatings. The second is
the development of a computer simulation tool that allows for the
prediction of UV intensity throughout a hospital room.
Recently, Lumacept, Inc. introduced coatings that strongly reflect
germicidal UV light. These coatings look and act just like traditional
wall or ceiling paint, but rather than absorb almost all of the UV
light, they reflect most of it. By better dispersing UV light, surfaces
that would otherwise be in shadow can receive over 14 times more
UV (Figure 2). The benefits of this have been demonstrated by several
recent peer-reviewed studies. What an infection preventionist can
expect to gain depends on the type of device being used.
Sensor based devices. Some UV disinfection devices are
designed to use UV sensors to measure the amount of light reflected
back to the device. These measurements are taken in several directions
and are used to determine the cycle time of the device. Lumacept
UV-reflective coatings were tested with one such device and the results
were published in Infection Control and Hospital Epidemiology. It
was determined that the use of reflective coatings reduced the cycle
time of the device by 80%. For example, during a cycle used to
disinfect MRSA, Lumacept coatings reduced the cycle time from 25
minutes to 5 minutes. MRSA samples were placed in 10 locations
throughout the room so that the disinfection effectiveness could be
determined. Despite the room being illuminated for 80% less time,
there was no loss of overall effectiveness. The C. diff. results were
similar: the cycle time was reduced from 44 minutes to 9 minutes, also
with no loss of effectiveness.
Fixed-cycle devices. Other UV devices operate using a fixed
cycle time. Based on the dimensions and layout of the room, the
manufacturer will make a treatment suggestion, though they are often
based purely on data from directly-illuminated surfaces. One fixed-
cycle device was recently studied in a hospital setting both with and
without Lumacept UV-reflective coatings. The cycle time was held
constant at 5 minutes during the MRSA trials and at 10
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light hits an
object, it can
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