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10
Most Dangerous Toxins in Your
Household
Biological
Pollutants in your home
Clear
your home of Asthma
Triggers
Preventing
Sinusitis
Residential
Air Cleaning Devices
Should
you have your Air Ducts
Cleaned
What
You Should Know About
Combustion Applicances
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What is Air Duct Cleaning?
Most people are now aware that indoor air pollution is an issue
of growing concern and increased visibility. Many companies are
marketing products and services intended to improve the quality
of your indoor air. You have probably seen an advertisement, received
a coupon in the mail, or been approached directly by a company
offering to clean your air ducts as a means of improving your
home's indoor air quality. These services typically but not always
range in cost from $450 to $1,000 per heating and cooling system,
depending on the services offered, the size of the system to be
cleaned, system accessibility, climatic region, and level of contamination.
Duct cleaning generally refers to the cleaning of various heating
and cooling system components of forced air systems, including
the supply and return air ducts and registers, grilles and diffusers,
heat exchangers heating and cooling coils, condensate drain pans
(drip pans), fan motor and fan housing, and the air handling unit
housing (See diagram).
If not properly installed, maintained, and operated, these components
may become contaminated with particles of dust, pollen or other
debris. If moisture is present, the potential for microbiological
growth (e.g., mold) is increased and spores from such growth may
be released into the home's living space. Some of these contaminants
may cause allergic reactions or other symptoms in people if they
are exposed to them. If you decide to have your heating and cooling
system cleaned, it is important to make sure the service provider
agrees to clean all components of the system and is qualified
to do so. Failure to clean a component of a contaminated system
can result in re-contamination of the entire system, thus negating
any potential benefits. Methods of duct cleaning vary, although
standards have been established by industry associations concerned
with air duct cleaning. Typically, a service provider will use
specialized tools to dislodge dirt and other debris in ducts,
then vacuum them out with a high-powered vacuum cleaner.
In addition, the service provider may propose applying chemical
biocides, designed to kill microbiological contaminants, to the
inside of the ductwork and to other system components. Some service
providers may also suggest applying chemical treatments (sealants
or other encapsulants) to seal or cover the inside surfaces of
the air ducts and equipment housings because they believe the
sealant will control mold growth or prevent the release of dirt
particles or fibers from ducts. These practices have yet to be
fully researched and you should be fully informed before deciding
to permit the use of biocides or sealants in your air ducts. They
should only be applied, if at all, after the system has been properly
cleaned of all visible dust or debris.
Knowledge about the potential benefits and possible problems
of air duct cleaning is limited. Since conditions in every home
are different, it is impossible to generalize about whether or
not air duct cleaning in your home would be beneficial.
If no one in your household suffers from allergies or unexplained
symptoms or illnesses and if, after a visual inspection of the
inside of the ducts, you see no indication that your air ducts
are contaminated with large deposits of dust or mold (no musty
odor or visible mold growth), having your air ducts cleaned is
probably unnecessary. It is normal for the return registers to
get dusty as dust-laden air is pulled through the grate. This
does not indicate that your air ducts are contaminated with heavy
deposits of dust or debris; the registers can be easily vacuumed
or removed and cleaned.
On the other hand, if family members are experiencing unusual
or unexplained symptoms or illnesses that you think might be related
to your home environment, you should discuss the situation with
your doctor. EPA has published Indoor Air Quality: An Introduction
for Health Professionals that can be obtained free of charge by
contacting IAQ INFO at the number listed in this guide. You may
obtain another free EPA booklet from IAQ INFO entitled The Inside
Story: A Guide to Indoor Air Quality for guidance on identifying
possible indoor air quality problems and ways to prevent or fix
them.
You may consider having your air ducts cleaned simply because
it seems logical that air ducts will get dirty over time and should
occasionally be cleaned. While the debate about the value of periodic
duct cleaning continues, no evidence suggests that such cleaning
would be detrimental, provided that it is done properly.
On the other hand, if a service provider fails to follow proper
duct cleaning procedures, duct cleaning can cause indoor air problems.
For example, an inadequate vacuum collection system can release
more dust, dirt, and other contaminants than if you had left the
ducts alone. A careless or inadequately trained service provider
can damage your ducts or heating and cooling system, possibly
increasing your heating and air conditioning costs or forcing
you to undertake difficult and costly repairs or replacements.
You should consider having the air ducts in your home cleaned
if:
- There is substantial visible mold growth inside hard surface
(e.g., sheet metal) ducts or on other components of your heating
and cooling system. There are several important points to understand
concerning mold detection in heating and cooling systems:
- Many sections of your heating and cooling system may not be
accessible for a visible inspection, so ask the service provider
to show you any mold they say exists.
- You should be aware that although a substance may look like
mold, a positive determination of whether it is mold or not
can be made only by an expert and may require laboratory analysis
for final confirmation. For about $50, some microbiology laboratories
can tell you whether a sample sent to them on a clear strip
of sticky household tape is mold or simply a substance that
resembles it.
- If you have insulated air ducts and the insulation gets wet
or moldy it cannot be effectively cleaned and should be removed
and replaced. If the conditions causing the mold growth in the
first place are not corrected, mold growth will recur.
- Ducts are infested with vermin, e.g. (rodents or insects);
or
- Ducts are clogged with excessive amounts of dust and debris
and/or particles are actually released into the home from your
supply registers.
Other Important Considerations...
Duct cleaning has never been shown to actually prevent health
problems. Neither do studies conclusively demonstrate that particle
(e.g., dust) levels in homes increase because of dirty air ducts
or go down after cleaning. This is because much of the dirt that
may accumulate inside air ducts adheres to duct surfaces and does
not necessarily enter the living space. It is important to keep
in mind that dirty air ducts are only one of many possible sources
of particles that are present in homes. Pollutants that enter
the home both from outdoors and indoor activities such as cooking,
cleaning, smoking, or just moving around can cause greater exposure
to contaminants than dirty air ducts. Moreover, there is no evidence
that a light amount of household dust or other particulate matter
in air ducts poses any risk to health.
EPA does not recommend that air ducts be cleaned except on an
as-needed basis because of the continuing uncertainty about the
benefits of duct cleaning under most circumstances. If a service
provider or advertiser asserts that EPA recommends routine duct
cleaning or makes claims about its health benefits, you should
notify EPA by writing to the address listed at the end of this
guidance. EPA does, however, recommend that if you have a fuel
burning furnace, stove, or fireplace, they be inspected for proper
functioning and serviced before each heating season to protect
against carbon monoxide poisoning. Some research also suggests
that cleaning dirty cooling coils, fans and heat exchangers can
improve the efficiency of heating and cooling systems. However,
little evidence exists to indicate that simply cleaning the duct
system will increase your system's efficiency.
If you think duct cleaning might be a good idea for your home,
but you are not sure, talk to a professional. The company that
services your heating and cooling system may be a good source
of advice. You may also want to contact professional duct cleaning
service providers and ask them about the services they provide.
Remember, they are trying to sell you a service, so ask questions
and insist on complete and knowledgeable answers.
Suggestions for Choosing a Duct Cleaning Service Provider
Do not assume that all duct cleaning service providers are equally
knowledgeable and responsible. Talk to at least three different
service providers and get written estimates before deciding whether
to have your ducts cleaned. When the service providers come to
your home, ask them to show you the contamination that would justify
having your ducts cleaned.
Do not hire duct cleaners who make sweeping claims about the
health benefits of duct cleaning such claims are unsubstantiated.
Do not hire duct cleaners who recommend duct cleaning as a routine
part of your heating and cooling system maintenance. You should
also be wary of duct cleaners who claim to be certified by EPA.
EPA neither establishes duct cleaning standards nor certifies,
endorses, or approves duct cleaning companies.
Do not allow the use of chemical biocides or sealants unless
you fully understand the pros and the cons (See "Unresolved
Issues of Duct Cleaning).
Check references to be sure other customers were satisfied and
did not experience any problems with their heating and cooling
system after cleaning.
Contact your county or city office of consumer affairs or local
Better Business Bureau to determine if complaints have been lodged
against any of the companies you are considering.
Interview potential service providers to ensure:
- they are experienced in duct cleaning and have worked on systems
like yours;
- they will use procedures to protect you, your pets, and your
home from contamination; and
- they comply with NADCA's air duct cleaning standards and,
if your ducts are constructed of fiber glass duct board or insulated
internally with fiber glass duct liner, with the North American
Insulation Manufacturers Association's (NAIMA) recommendations.
If the service provider charges by the hour, request an estimate
of the number of hours or days the job will take, and find out
whether there will be interruptions in the work. Make sure the
duct cleaner you choose will provide a written agreement outlining
the total cost and scope of the job before work begins.
What to Expect From an Air Duct Cleaning Service Provider
If you choose to have your ducts cleaned, the service provider
should:
- Open access ports or doors to allow the entire system to be
cleaned and inspected.
- Inspect the system before cleaning to be sure that there are
no asbestos-containing materials (e.g., insulation, register
boots, etc.) in the heating and cooling system. Asbestos-containing
materials require specialized procedures and should not be disturbed
or removed except by specially trained and equipped contractors.
- Use vacuum equipment that exhausts particles outside of the
home or use only high-efficiency particle air (HEPA) vacuuming
equipment if the vacuum exhausts inside the home.
- Protect carpet and household furnishings during cleaning.
- Use well-controlled brushing of duct surfaces in conjunction
with contact vacuum cleaning to dislodge dust and other particles.
- Use only soft-bristled brushes for fiberglass duct board and
sheet metal ducts internally lined with fiberglass. (Although
flex duct can also be cleaned using soft-bristled brushes, it
can be more economical to simply replace accessible flex duct.)
- Take care to protect the ductwork, including sealing and re-insulating
any access holes the service provider may have made or used
so they are airtight.
- Follow NADCA's standards for air duct cleaning and NAIMA's
recommended practice for ducts containing fiber glass lining
or constructed of fiber glass duct board.
How to Determine if the Duct Cleaner Did a Thorough Job
A thorough visual inspection is the best way to verify the cleanliness
of your heating and cooling system. Some service providers use
remote photography to document conditions inside ducts. All portions
of the system should be visibly clean; you should not be able
to detect any debris with the naked eye. Show the Post-Cleaning
Consumer Checklist to the service provider before the work begins.
After completing the job, ask the service provider to show you
each component of your system to verify that the job was performed
satisfactorily.
If you answer "No" to any of the questions on the checklist,
this may indicate a problem with the job. Ask your service provider
to correct any deficiencies until you can answer "yes"
to all the questions on the checklist.
Post-Cleaning Consumer Checklist:
Yes / No General
- Did the service provider obtain access to and clean the entire
heating and cooling system, including ductwork and all components
(drain pans, humidifiers, coils, and fans)?
- Has the service provider adequately demonstrated that ductwork
and plenums are clean? (Plenum is a space in which supply or
return air is mixed or moves; can be duct, joist space, attic
and crawl spaces, or wall cavity.) - Heating
- Is the heat exchanger surface visibly clean? - Cooling Components
- Are both sides of the cooling coil visibly clean?
- If you point a flashlight into the cooling coil, does light
shine through the other side? It should if the coil is clean.
- Are the coil fins straight and evenly spaced (as opposed to
being bent over and smashed together)?
- Is the coil drain pan completely clean and draining properly?
- Blower
- Are the blower blades clean and free of oil and debris?
- Is the blower compartment free of visible dust or debris?
- Plenums
- Is the return air plenum free of visible dust or debris?
- Do filters fit properly and are they the proper efficiency
as recommended by HVAC system manufacturer?
- Is the supply air plenum (directly downstream of the air handling
unit) free of moisture stains and contaminants? Metal Ducts
- Are interior ductwork surfaces free of visible debris? (Select
several sites at random in both the return and supply sides
of the system.) - Fiber Glass
- Is all fiber glass material in good condition (i.e., free
of tears and abrasions; well adhered to underlying materials)?
- Access Doors
- Are newly installed access doors in sheet metal ducts attached
with more than just duct tape (e.g., screws, rivets, mastic,
etc.)?
- With the system running, is air leakage through access doors
or covers very slight or non-existent? - Air Vents
- Have all registers, grilles, and diffusers been firmly reattached
to the walls, floors, and/or ceilings?
- Are the registers, grilles, and diffusers visibly clean? System
Operation
Does the system function properly in both the heating and cooling
modes after cleaning?
How to Prevent Duct Contamination
Whether or not you decide to have the air ducts in your home
cleaned, committing to a good preventive maintenance program is
essential to minimize duct contamination.
To prevent dirt from entering the system:
- Use the highest efficiency air filter recommended by the manufacturer
of your heating and cooling system.
- Change filters regularly.
- If your filters become clogged, change them more frequently.
- Be sure you do not have any missing filters and that air cannot
bypass filters through gaps around the filter holder.
- When having your heating and cooling system maintained or
checked for other reasons, be sure to ask the service provider
to clean cooling coils and drain pans.
- During construction or renovation work that produces dust
in your home, seal off supply and return registers and do not
operate the heating and cooling system until after cleaning
up the dust.
- Remove dust and vacuum your home regularly. (Use a high efficiency
vacuum (HEPA) cleaner or the highest efficiency filter bags
your vacuum cleaner can take. Vacuuming can increase the amount
of dust in the air during and after vacuuming as well as in
your ducts).
- If your heating system includes in-duct humidification equipment,
be sure to operate and maintain the humidifier strictly as recommended
by the manufacturer.
To prevent ducts from becoming wet:
Moisture should not be present in ducts. Controlling moisture
is the most effective way to prevent biological growth in air
ducts.
- Moisture can enter the duct system through leaks or if the
system has been improperly installed or serviced. Research suggests
that condensation (which occurs when a surface temperature is
lower than the dew point temperature of the surrounding air)
on or near cooling coils of air conditioning units is a major
factor in moisture contamination of the system. The presence
of condensation or high relative humidity is an important indicator
of the potential for mold growth on any type of duct. Controlling
moisture can often be difficult, but here are some steps you
can take:
- Promptly and properly repair any leaks or water damage.
- Pay particular attention to cooling coils, which are designed
to remove water from the air and can be a major source of moisture
contamination of the system that can lead to mold growth. Make
sure the condensate pan drains properly. The presence of substantial
standing water and/or debris indicates a problem requiring immediate
attention. Check any insulation near cooling coils for wet spots.
- Make sure ducts are properly sealed and insulated in all non-air-conditioned
spaces (e.g., attics and crawl spaces). This will help to prevent
moisture due to condensation from entering the system and is
important to make the system work as intended. To prevent water
condensation, the heating and cooling system must be properly
insulated.
- If you are replacing your air conditioning system, make sure
that the unit is the proper size for your needs and that all
ducts are sealed at the joints. A unit that is too big will
cycle on an off frequently, resulting in poor moisture removal,
particularly in areas with high humidity. Also make sure that
your new system is designed to manage condensation effectively.
Unresolved Issues of Duct Cleaning
Does duct cleaning prevent health problems?
The bottom line is: no one knows. There are examples of ducts
that have become badly contaminated with a variety of materials
that may pose risks to your health. The duct system can serve
as a means to distribute these contaminants throughout a home.
In these cases, duct cleaning may make sense. However, a light
amount of household dust in your air ducts is normal. Duct cleaning
is not considered to be a necessary part of yearly maintenance
of your heating and cooling system, which consists of regular
cleaning of drain pans and heating and cooling coils, regular
filter changes and yearly inspections of heating equipment. Research
continues in an effort to evaluate the potential benefits of air
duct cleaning.
In the meantime educate yourself about duct cleaning by contacting
some or all of the sources of information listed at the end of
this publication and asking questions of potential service providers.
Are duct materials other than bare sheet metal ducts more
likely to be contaminated with mold and other biological contaminants?
You may be familiar with air ducts that are constructed of sheet
metal. However, many modern residential air duct systems are constructed
of fiber glass duct board or sheet metal ducts that are lined
on the inside with fiber glass duct liner. Since the early 1970's,
a significant increase in the use of flexible duct, which generally
is internally lined with plastic or some other type of material,
has occurred. The use of insulated duct material has increased
due to improved temperature control, energy conservation, and
reduced condensation. Internal insulation provides better acoustical
(noise) control. Flexible duct is very low cost. These products
are engineered specifically for use in ducts or as ducts themselves,
and are tested in accordance with standards established by Underwriters
Laboratories (UL), the American Society for Testing and Materials
(ASTM), and the National Fire Protection Association (NFPA).
Many insulated duct systems have operated for years without supporting
significant mold growth. Keeping them reasonably clean and dry
is generally adequate. However, there is substantial debate about
whether porous insulation materials (e.g., fiber glass) are more
prone to microbial contamination than bare sheet metal ducts.
If enough dirt and moisture are permitted to enter the duct system,
there may be no significant difference in the rate or extent of
microbial growth in internally lined or bare sheet metal ducts.
However, treatment of mold contamination on bare sheet metal is
much easier. Cleaning and treatment with an EPA-registered biocide
are possible. Once fiberglass duct liner is contaminated with
mold, cleaning is not sufficient to prevent regrowth and there
are no EPA-registered biocides for the treatment of porous duct
materials. EPA, NADCA, and NAIMA all recommend the replacement
of wet or moldy fiber glass duct material.
In the meantime experts do agree that moisture should not be
present in ducts and if moisture and dirt are present, the potential
exists for biological contaminants to grow and be distributed
throughout the home. Controlling moisture is the most effective
way to prevent biological growth in all types of air ducts.
- Correct any water leaks or standing water.
- Remove standing water under cooling coils of air handling
units by making sure that drain pans slope toward the drain.
- If humidifiers are used, they must be properly maintained.
- Air handling units should be constructed so that maintenance
personnel have easy, direct access to heat exchange components
and drain pans for proper cleaning and maintenance.
- Fiber glass, or any other insulation material that is wet
or visibly moldy (or if an unacceptable odor is present) should
be removed and replaced by a qualified heating and cooling system
contractor.
- Steam cleaning and other methods involving moisture should
not be used on any kind of ductwork.
Should chemical biocides be applied to the inside of air ducts?
Air duct cleaning service providers may tell you that they need
to apply a chemical biocide to the inside of your ducts to kill
bacteria (germs), and fungi (mold) and prevent future biological
growth. Some duct cleaning service providers may propose to introduce
ozone to kill biological contaminants. Ozone is a highly reactive
gas that is regulated in the outside air as a lung irritant. However,
there remains considerable controversy over the necessity and
wisdom of introducing chemical biocides or ozone into the ductwork.
Among the possible problems with biocide and ozone application
in air ducts:
- Little research has been conducted to demonstrate the effectiveness
of most biocides and ozone when used inside ducts. Simply spraying
or otherwise introducing these materials into the operating
duct system may cause much of the material to be transported
through the system and released into other areas of your home.
- Some people may react negatively to the biocide or ozone,
causing adverse health reactions.
Chemical biocides are regulated by EPA under Federal pesticide
law. A product must be registered by EPA for a specific use before
it can be legally used for that purpose. The specific use(s) must
appear on the pesticide (e.g., biocide) label, along with other
important information. It is a violation of federal law to use
a pesticide product in any manner inconsistent with the label
directions.
A small number of products are currently registered by EPA specifically
for use on the inside of bare sheet metal air ducts. A number
of products are also registered for use as sanitizers on hard
surfaces, which could include the interior of bare sheet metal
ducts. While many such products may be used legally inside of
unlined ducts if all label directions are followed, some of the
directions on the label may be inappropriate for use in ducts.
For example, if the directions indicate "rinse with water",
the added moisture could stimulate mold growth.
All of the products discussed above are registered solely for
the purpose of sanitizing the smooth surfaces of unlined (bare)
sheet metal ducts. No products are currently registered as biocides
for use on fiber glass duct board or fiber glass lined ducts,
so it is important to determine if sections of your system contain
these materials before permitting the application of any biocide.
In the meantime before allowing a service provider to use a chemical
biocide in your ductwork, the service provider should:
- Demonstrate visible evidence of microbial growth in your ductwork.
Some service providers may attempt to convince you that your
air ducts are contaminated by demonstrating that the microorganisms
found in your home grow on a settling plate (i.e., petri dish).
This is inappropriate. Some microorganisms are always present
in the air, and some growth on a settling plate is normal. As
noted earlier, only an expert can positively identify a substance
as biological growth and lab analysis may be required for final
confirmation. Other testing methods are not reliable.
- Explain why biological growth cannot be removed by physical
means, such as brushing, and further growth prevented by controlling
moisture.
- If you decide to permit the use of a biocide, the service
provider should:
- Show you the biocide label, which will describe its range
of approved uses.
- Apply the biocide only to un-insulated areas of the duct system
after proper cleaning, if necessary to reduce the chances for
re-growth of mold.
- Always use the product strictly according to its label instructions.
While some low toxicity products may be legally applied while
occupants of the home are present, you may wish to consider leaving
the premises while the biocide is being applied as an added precaution.
Do sealants prevent the release of dust and dirt particles
into the air?
Manufacturers of products marketed to coat and seal duct surfaces
claim that these sealants prevent dust and dirt particles inside
air ducts from being released into the air. As with biocides,
a sealant is often applied by spraying it into the operating duct
system. Laboratory tests indicate that materials introduced in
this manner tend not to completely coat the duct surface. Application
of sealants may also affect the acoustical (noise) and fire retarding
characteristics of fiber glass lined or constructed ducts and
may invalidate the manufacturer's warranty.
Questions about the safety, effectiveness and overall desirability
of sealants remain. For example, little is known about the potential
toxicity of these products under typical use conditions or in
the event they catch fire.
In addition, sealants have yet to be evaluated for their resistance
to deterioration over time which could add particles to the duct
air.
Checklist to Know if the Job's been Done Right
- Learn as much as possible about air duct cleaning before you
decide to have your ducts cleaned by reading this guidance and
contacting the sources of information provided.
- Consider other possible sources of indoor air pollution first
if you suspect an indoor air quality problem exists in your
home.
- Have your air ducts cleaned if they are visibly contaminated
with substantial mold growth, pests or vermin, or are clogged
with substantial deposits of dust or debris.
- Ask the service provider to show you any mold or other biological
contamination they say exists. Get laboratory confirmation of
mold growth or decide to rely on your own judgment and common
sense in evaluating apparent mold growth.
- Check references.
- Insist that the service provider give you knowledgeable and
complete answers to your questions.
- Find out whether your ducts are made of sheet metal, flex
duct, or constructed of fiber glass duct board or lined with
fiber glass since the methods of cleaning vary depending on
duct type. Remember, a combination of these elements may be
present.
- Permit the application of biocides in your ducts only if necessary
to control mold growth and only after assuring yourself that
the product will be applied strictly according to label directions.
As a precaution, you and your pets should leave the premises
during application.
- Do not permit the use of sealants except under unusual circumstances
where other alternatives are not feasible.
- Commit to a preventive maintenance program of yearly inspections
of your heating and cooling system, regular filter changes,
and steps to prevent moisture contamination.
To Learn More About Indoor Air Quality
- U.S. Environmental Protection Agency Office of Radiation and
Indoor Air Indoor Environments Division (6604J) 401 M St., S.W.
Washington, DC 20460 (202) 564-9370 (202) 565-2038 (fax) E-mail:
webmaster.oria@epamail.epa.gov World Wide Web Site: http://www.epa.gov/iaq/
- Indoor Air Quality Information Clearinghouse (IAQ INFO) P.O.
Box 37133 Washington, DC 20013-7133 1 (800) 438-4318 (202) 484-1307
E-mail: IAQINFO@aol.com
- Useful EPA publications available free of charge from either
location above:
- The Inside Story: A Guide to Indoor Air Quality Indoor Air
Pollution: An Introduction for Health Professionals Residential
Air Cleaning Devices: A Summary of Available Information
- Consumer Research Council (CRC) IAQ Checklist P.O. Box 12099
Washington, DC 20005-0999
- Ask for: How Healthy Is The Air In Your Home? (Free. Send
a self-addressed, stamped standard size business envelope)
To Learn More About Air Duct Cleaning
- National Air Duct Cleaners Association (NADCA) 1518 K Street,
NW Suite 503 Washington, DC 20005 (202) 737-2926 http://www.nadca.com
Ask for: Introduction to HVAC (Heating, Ventilating, and Air
Conditioning) System Cleaning Services (Although intended for
commercial customers, information can be useful to consumers.)
- North American Insulation Manufacturers Association (NAIMA)
44 Canal Center Plaza, Suite 310 Alexandria, VA 22314 (703)
684-0084 Ask for: Cleaning Fibrous Glass Insulated Air Duct
Systems; Recommended Practice
Other Useful Resources
- For a free list of state and local consumer protection agencies
and Better Business Bureaus:
- Consumer's Resource Handbook Consumer Information Center Pueblo,
CO 81009
- For Information on Antimicrobial Biocides:
National Antimicrobial Information Network (NAIN) 1 (800) 447-6349
October 1997
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