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Follow @HFTodayMi piaceBy Forrest Fencl / Special to Healthcare Facilities Today June 9, 2014
« MAINTENANCE AND OPERATIONS
Hospital infection control:
reducing airborne
pathogens
Much attention is
focused today on
pathogenic
microorganisms that
have developed
resistance to antibiotic
treatment, or entire
types or classes of
antibiotics. The loss of
effective antibiotic treatment undermines the ability of
healthcare professionals to fight infectious diseases and
manage their complications among immunocompromised
patients.
The Centers for Disease Control and Prevention (CDC) estimates
that more than two million people in the United States are
sickened every year with antibiotic-resistant infections, with at
least 75,000 dying (2013) as a result. Healthcare associated
infections (HAIs) kill more people in this country than AIDS,
Information and insight for the healthcare facility team
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breast cancer and auto accidents combined.
Healthcare associated infections are also known as nosocomial
infections or hospital-acquired infections. They are transmitted
by a variety of vectors, including person-to-person, through
injection/insertion of medical devices, airborne contact of open
wounds, and by respiration of airborne particles. Some
emerging diseases, such as Middle East Respiratory Syndrome
(MERS) are not yet understood well enough to positively
identify the transmission vector.
The most dangerous HAI pathogens are those that have the
potential to spread by the airborne route (Kowalski 2006).Many of these pathogens, such as Methicillin-resistant
Staphylococcus aureus (MRSA), are now called “superbugs”
because they are virtually invincible to standard drug
treatments. Favorable indoor environments tend to self-
perpetuate these agents, adding to the concern by infection
control specialists everywhere.
According to the CDC and World Health Organization,
antibiotic-resistant HAIs are on the rise. Support for airborne
disease transmission is also on the rise (Fletcher et al. 2003).Evidence exists for airborne nosocomial transmissions of
Acinetobacter, Pseudomonas, and MRSA (Allen and Green1987), (Ryan et al. 2011) and (Farrington et al. 1990), and
airborne transmission can spread rapidly and pervasively
through a non-immune population (Weinstein 2004).
If mechanical and functional operations have remained
unchanged, other sources of drug-resistant contamination
must exist, presumably associated also with allusive paths of
transmission. Therefore, source and pathway management
should involve airborne transmission and especially enhanced
methods of its control even though the primary route is
considered to be direct contact. This article discusses several
control methods.
Infection controls
Addressing infection control in hospitals requires integrating
HVAC and air-pressure-control with dedicated infection-control
systems, and minimizing unplanned airflows through building
envelopes and interior spaces. It also benefits from the
application of ultraviolet UV-C equipment from what is
typically referred to in the healthcare industry (and the CDC) as
ultraviolet germicidal irradiation (UVGI).
There are four methods used to reduce the concentrations of
airborne infectious agents: dilution, filtration, pressurization,
and disinfection. Following is a brief discussion of each
method, with a focus on disinfection.
Dilution
Dilution ventilation helps to control infectious particles by
introducing outdoor air, usually 2 to 5 air changes/hour (ACH),
to dilute space air and then exhausting that amount as
contaminated air. If 100 percent of all supply air were outdoor
air, nearly that amount of airborne infectious particles might
be exhausted. However, conditioning that amount of outdoor
air would be cost prohibitive and therefore considered out of
the question.
Filtration
The combination of filtration equipment and airflow rates are
often misunderstood or underappreciated for the effect they
have on the concentration of infectious agents in any
conditioned space. Filtration should be considered healthcare’s
first line of defense against infectious agents as it removes a
large percentage of them with every complete air change
through an air handler. If the filter efficiency and/or air change
rate is increased, a larger number of infectious agents would
be removed per pass.
Therefore, it’s important to view the return air and filtration
system as a removal method of space generated contaminants -
and not the air distribution side as a pathogen source, with the
possible exception of some smaller viral particles. If there is
concern here, the application of UV-C in the air handler
equipment is warranted.
Current design guidelines suggest air change rates up to 25 (up
to five of them as outdoor air) for new facilities, depending on
the space served. Because most of the airborne pathogens
originate from patients and room occupants, increasing the
rates of supply air above design guidelines will bring
diminishing returns. Thus, the incremental benefit in
preventing cross-transmission is much more difficult to
demonstrate beyond 25 ACH. This can be seen in this simple
equation:
Concentration (particles/cu.ft)= generation rate (no. of
people/activity)
cfm x filter eff. (removal rate)
If either the cfm or filter efficiency is increased, the particle
concentrations will decrease mathematically. However, the
algorithm favors reducing in-room source or generation rates
of infectious agents, often referred to as source control or
source reduction.
Pressurization
Pressurization protects against cross contamination from the
infiltration of air from one space type to that of another. This is
of great importance in healthcare settings, but it is very
difficult to control. Frequently opened or propped open doors
are all too common making corridors, etc., a conduit of
contaminated air to other spaces. Although ORs and other
areas are designed to be under positive pressure with respect
to external spaces, this may not be the case when an air
handler’s airflow has been compromised!
Note that air handler design resistance is the sum of all
pressure losses through the system, including elbows, dampers,
filters and coils, etc. The shape of a resistance curve will
change when pressure losses change (Greenheck 1999). For
instance, as filter resistance increases, system air volume is
reduced. But, like the filter, it’s also common for the coil
pressure drop to increase, even double, which will result in a
higher system pressure drop as well. The curves show that as
the system’s total resistance increases, air volume and system
pressure capability are reduced (at a constant fan RPM). This
reduction in ‘design-pressure’ occurs often today from reduced
coil cleaning procedures, but its effect is not at all obvious, and
it’s not just a reduction in air volume, although that’s
important, it’s also a reduction in relative room pressure
capability! When one space is said to be negative in relation to
other spaces, it assumes that the adjoining spaces are all
‘positive’. A higher coil pressure drop will potentially negate
that and permit the infiltration of contaminated air.
Measuring the pressure drop across a coil and comparing it to
as-built design data, or better, the manufacturer’s coil
performance data, is one way to determine a potential loss in
airflow. If the coil pressure drop is higher, the actual airflow
should be measured to confirm that it matches as-built criteria.
If the coil is fouled (common) and air pressure compromised,
the 2011 ASHRAE Handbook – HVAC Applications recommends
the installation of UV-C lamps to clean the coil and keep it clean
continuously. A clean coil will assure proper airflow and
pressure relationships with the added benefit of restoring as-
built cooling capacity (i.e., the heat-transfer characteristics).
According to ASHRAE, UV-C will also eliminate the growth of
coil plenum mold and bacteria removing the possibility of
microbial products carryover and transfer to conditioned
spaces.
Disinfection
In addition to opening and propping open of doors as a
contaminant transfer mode, the entering and exiting of people
also provides a contaminant source. It’s known that the
concentration of airborne bacteria is proportional to the
number of personnel in the room (Mangram et al. 1999, Duvlisand Drescher 1980, Moggio et al. 1979, Kundsin 1976). The
amount of surface contamination is also related to airborne
contamination from occupation and activity since these
microbes settle continuously. The World Health Organization
(WHO 1998) recommends a limit of 100 cfu (colony forming
units)/m3 for bacteria and 50 cfu/m3 for fungi for sensitive
areas. There are no published cfu standards in the U.S.
While the use of UV-C equipment, or disinfection, to control
infectious agents in healthcare settings is one of its oldest uses,
today the technology is under-utilized. In the past seventy
years it has used to disinfect upper air, ventilation air, and to
sterilize medical equipment and water, with measured and
successful results. However, its use waned as dependence on
antibiotics began in the late 1950s and beyond. UV-C destroys
all microorganisms… and its use is extremely simple and
inexpensive, but like all controls, it alone is not a complete
answer.
UV-C for infection control
There are three primary means of applying UV-C systems
against infectious agents: upper-air (upper-room), coil
irradiation, and airstream disinfection. Upper-air systems are
installed in room spaces, such as above patient beds and in
waiting rooms, corridors and break areas, etc. Coil irradiation
and airstream disinfection systems are installed within air
handling units or duct runs. Upper room and HVAC
applications are described below.
Upper Air/Room
The primary objective of upper-air UV-C placement is to
interrupt the transmission of airborne infectious diseases in
patient rooms, waiting rooms and other known microbial
pathways such as lobbies, stairwells, laundry chutes, and
emergency entrances and corridors, all of which can be
effectively and affordably treated with UV-C (ASHRAE 2011).
Airborne droplets containing infectious agents can remain in
room air for 6 minutes and longer. Upper Air UV-C fixtures can
destroy those microbes in a matter of seconds. Operating 24
hours a day, upper-air systems are also especially effective at
notably reducing the potential viability of surface microbes
that settle out of room air.
Humans are the source of airborne agents which infect people
(Nardell and Macher: ACGIH 1999). Again, upper-air systems
intercept microbes where they are generated, thereby
controlling them at the source (First et al. 1999). They have
been shown to be effective against viruses and bacteria,
including chickenpox, measles, mumps, varicella, TB, and cold
viruses. Studies of Mycobacterium tuberculosis have shown
that they can be equivalent to 10–25 air changes per hour (CDC2005). In a study by Escombe et al. (2009), guinea pigs were
exposed to exhaust air from a TB ward, of which 35 percent of
the controls developed TB infections while only 9.5 percent
developed infections where upper air UV-C was used, yielding
a decrease of 74 percent in the infection rate.
Measles and influenza viruses and the tuberculosis bacteria
are diseases known to be transmitted by means of shared air
between infected and susceptible persons. Studies indicate
that there are two transmission patterns: (I) within-room
exposure such as in a congregate space; (II) transmissions
beyond a room through corridors, and through entrainment
within ventilation ductwork where air is then recirculated
throughout the building. Since the 1930s (Wells 1955; Riley andO’Grady 1961) and continuing to the present day (Miller et al.2002; Xu et al. 2003; First et al. 2007), numerous experimental
studies have demonstrated the efficacy of upper-air UV-C. In
addition, effectiveness has been shown for reducing measles
transmission in a school, and influenza transmission within a
hospital (McLean 1961). What’s more, newer fixtures available
today provide more output and coverage at less cost and
power. They also utilize inexpensive and commonly available
lamps!
HVAC systems
HVAC systems provide an excellent growth area for mold and
some bacteria in and around cooling coils; drain pans (Levetinet al. 2001), plenum walls and filters. Growth of these microbial
deposits also leads to coil fouling which will increase coil
pressure drop and reduce airflow and heat exchange efficiency
(Montgomery and Baker 2006). As performance degrades, so
does the quality, amount and pressurization capability of air
supplied to conditioned spaces (Kowalski 2006/2009).
Because hospital codes call for high-efficiency filters to be
located downstream of the cooling coil, they can also become
damp and often wet from saturated air in that location. As
such, air filters are considered a growth medium for mold and
bacteria and an infectious-disease agent reservoir. ASHRAE
recommends UV-C lighting to be installed downstream of the
cooling coil; so if a 360 degree UV-C system is installed there, it
will disinfect both the coil and the filter to destroy all microbes
in and upon both devices. It should also be noted that when
using a 360-degree lamp in a “common” coil-irradiation system,
it will also kill infectious diseases in the airstream. For
example, up to a 35 percent kill ratio of many infectious agents
is achieved, thus providing a measurable increase in the
combined removal rate of the two devices (Kowalski 2009).
UV-C design guidance
Importantly, science has not found a microorganism that is
resistant to the destructive effects of the 254-nm germicidal
wavelength, including superbugs and all other microbes
associated with HAIs. The question then – how are UV-C
systems sized and applied?
Historically, engineers and facility practitioners wanting to
apply UV-C lacked specific guidance for systems design, sizing
and specifications. ASHRAE undertook the process by forming
a technical committee (TC 2.9 Ultraviolet Air and SurfaceTreatment) to author chapters in their 2008, 2011, and 2012
ASHRAE Handbooks, which have been referenced herein.
HVAC trade publications have also published several technical
articles to help provide additional design guidance; these
articles are cited in the sidebar, Technical Articles for
Engineers. In total, these articles provide all practitioners with
the guidance needed to successfully design, install, operate,
and maintain successful UV-C applications in HVAC systems.
UV-C at large
UV-C's rising popularity beyond ASHRAE has also generated
research by lesser-known organizations, such as the Air
Purification Consortium (APC); the Air Cleaning Industry
Expert Advisory Panel (ACIEAP); and The National Center for
Energy Management and Building Technologies (NCEMBT). UV-
C energy has been crucial to achieving each of their goals,
whether to save energy, reduce biological contamination and
maintenance or to reduce absenteeism. Their members are
involved in high-stakes projects such as Homeland Security
where application of UV-C is a crucial defense against
bioterrorism.
Safety & handling
Opening air handler doors to fan sections must be minimized
because it allows unfiltered air to enter and be dispersed to
potentially sensitive areas, and/or it will disrupt pressure
relationships in the spaces served by them. Shutting these
systems down can also disrupt pressure relationships beyond
the spaces served. Both of these functions, when necessary,
should be coordinated with floor nurses so that all room doors
may be closed before hand. Exposing filter surfaces to UV-C is
an effective way to destroy microbes on media surfaces.
However, synthetic media filters are not compatible with UV-C
while filters with glass media are. Caution should also be
exercised when using unsupported “bag” style filters as they
inherently collapse when being replaced to expel potentially
microbe- laden contamination. The CDC also recommends that
all used filters be bagged upon removal to prevent dispersion
of microbial contamination during transport.
Where installed, facility staff should be trained how to inspect
UV-C systems to ensure they are working properly. Controls
should be installed to turn UV-C systems off when air-handler
doors are opened. Eye and skin protection are needed to
prevent exposure to UV-C light when working in any area
where the lamps are on.
UV-C lamps are very similar in construction to fluorescent
lamps, and therefore contain trace amounts of mercury. The
use of encapsulated lamps is recommended to prevent air-
handler contamination should lamp breakage occur. Like
fluorescent lamps, UV-C lamps should be replaced and recycled
annually in a scheduled fashion.
Conclusion
UV-C installations are a simple, effective, and relatively
inexpensive means of reducing concentrations of airborne and
surface pathogens that cause healthcare associated infections.
Within patient rooms, waiting rooms, and other congregational
areas, upper-air UV-C units will kill airborne microorganisms
that inherently circulate into the path of the UV-C light. UV-C
lamps can be installed within HVAC systems downstream of
cooling coils to keep coils clean and to provide supplemental
kill ratios in airstreams and on filter surfaces. Recent guidance
from ASHRAE and published technical articles in HVAC trades
provide healthcare engineers and facility staff with the
resources needed to size, select, install, operate, and maintain
UV-C systems.
Design considerations
• Concentration of airborne infectious agents is directly related
to people activity
• Humans are the source of drug resistant microorganisms that
effect humans
• Airborne transmission of infectious agents may be more
prevalent than proven
• UV-C inactivates and destroys microorganisms rendering
them harmless
• 70+ year old Upper Air UV-C technology is heavily researched
and proven effective
• Newer Upper Air UV-C units are more affordable and much
more effective
• At 6 ACH an aerosol of infectious agents can stay airborne for
10 minutes
• Upper Air UV can inactivate airborne infectious agents in a
matter of seconds
• Source management will always prove to be the most
effective means of control
• Increased coil pressure drop will lower system airflow and
space pressurization
• Bathing coils with UV-C cleans them, improves airflow and
heat transfer efficiency
Additional Tips
• Install UV-C on cooling coils and drain pans to kill mold and
restore airflow
• Manage room pressure relationships, especially during
visiting hours
• Review and manage all air handler service, especially filters
and change-outs
• Manage air handler shutdowns, access door openings and coil
pressure drop
• Install newer style upper air UV-C fixtures in all spaces
known for HAI’s
• Also install them in corridors and waiting rooms connected to
these areas
• Once airflow is restored, upgrade air filters and efficiencies
where possible
Forrest Fencl is the president of UV Resources, Santa Clarita,Calif. He can be reached at [email protected].
ACGIH. 1999. Bioaerosols: Assessment and control, Ch. 9:Respiratory infections—Transmission and environmental control,by E.A. Nardell and J.M. Macher. American Conference onGovernmental Industrial Hygienists, Cincinnati, OH.Allen K, Green H. 1987. Hospital outbreak of multi-resistantAcinetobacter anitratus: An airborne mode of spread? J HospInfect 9:110–119.ASHRAE, 2011 Handbook – HVAC Applications, Chapter 60 –ULTRAVIOLET AIR AND SURFACE TREATMENT. Atlanta, GA.CDC. 2005. Guidelines for preventing the transmission ofMycobacterium tuberculosis in health-care settings. Morbidity andMortality Weekly Report (MMWR) 37-38, 70-75.Duvlis Z, Drescher J. 1980. Investigations on the concentration ofair-borne germs in conventionally air-conditioned operatingtheaters. Zentralbl Bakteriol [B] 170(1–2):185–198.Escombe, A.R., R.H. Gilman, M. Navincopa, E. Ticona, B. Mitchell,C. Noakes, C. Martínez, P. Sheen, R. Ramirez, W. Quino, A.Gonzalez, J.S. Friedland, and C.A. Evans. 2009. Upper-roomultraviolet light and negative air ionization to prevent tuberculosistransmission. PLoS Med 17(6).Farrington M, Ling T, French G. 1990. Outbreaks of infection withmethicillin-resistant Staphylococcus aureus on neonatal and burnsunits of a new hospital. Epidem Infect 105:215–228.First MW, Nardell EA, Chaisson W, Riley R. 1999. Guidelines forthe application of upper-room ultraviolet germicidal irradiation forpreventing transmission of airborne contagion – Part II: Designand operational guidance. ASHRAE J 105:869–876.First, M.W., F.M. Rudnick, K. Banahan, R.L. Vincent, and P.W.Brickner. 2007a. Fundamental factors affecting upper-roomultraviolet germicidal irradiation—Part 1: Experimental. Journalof Environmental Health 4: 1-11.Fletcher LA, Noakes CJ, Beggs CB, Sleigh PA, Kerr KG. 2003. TheUltraviolet Susceptibility of Aerosolised Microorganisms and theRole of Photoreactivation. Vienna: IUVA.GREENHECK, 1999 – Product Application Guide, Fan ApplicationNo. FA/100-99Kowalski, W.J. 2006. Aerobiological engineering handbook.McGraw-Hill, New York.Kowalski, W. 2009. Ultraviolet germicidal irradiation handbook.Springer-Verlag, Berlin.Kundsin R. 1976. Operating Room as a Source of WoundContamination and Infection. National Research Council, NationalAcademy of Sciences, pp. 167–172.Levetin, E., R. Shaughnessy, C. Rogers, and R. Scheir. 2001.Effectiveness of germicidal UV radiation for reducing fungalcontamination within air-handling units. Applied andEnvironmental Microbiology 67(8):3712-3715.Mangram AJ, Horan TC, Pearson ML, Silver LC, Jarvis WR,HICPAC. 1999. Guideline for prevention of surgical site infection.Am J. Infect Control 27(2): 97–132.McLean R. 1961. The effect of ultraviolet radiation upon thetransmission of epidemic influenzain long-term hospital patients.Am Rev Resp Dis 83:36–38.Moggio M, Goldner JL, McCollum DE, Beissinger SF. 1979. Wound
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