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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 forrest.fencl@uvresources.com. 

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