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Biological Air Pollutants
Air
Pollutants in Relation to Disease
Biological air pollutants are found to some degree
in every home, school, and workplace. Sources include
outdoor air and human occupants who shed viruses and
bacteria, animal occupants (insects and other arthropods,
mammals) that shed allergens, and indoor surfaces
and water reservoirs where fungi and bacteria can
grow, such as humidifiers.23
A number of factors allow biological agents to grow
and be released into the air. Especially important
is high relative humidity, which encourages house
dust mite populations to increase and allows fungal
growth on damp surfaces. Mite and fungus contamination
can be caused by flooding, continually damp carpet
(which may occur when carpet is installed on poorly
ventilated concrete floors), inadequate exhaust of
bathrooms, or kitchen generated moisture.24
Appliances such as humidifiers, dehumidifiers, air
conditioners, and drip pans under cooling coils (as
in refrigerators), support the growth of bacteria
and fungi.
Components of mechanical heating, ventilating, and
air conditioning (HVAC) systems may also serve as
reservoirs or sites of microbial amplification.25
These include air intakes near potential sources of
contamination such as standing water, organic debris
or bird droppings, or integral parts of the mechanical
system itself, such as various humidification systems,
cooling coils, or condensate drain pans. Dust and
debris may be deposited in the duct work or mixing
boxes of the air handler.
Biological agents in indoor air are known to cause
three types of human disease: infections, where pathogens
invade human tissues; hypersensitivity disease, where
specific activation of the immune system causes disease;
and toxicoses, where biologically produced chemical
toxins cause direct toxic effects.
In addition, exposure to conditions conducive to biological
contamination (e.g. dampness, water damage) has been
related to nonspecific upper and lower respiratory
symptoms. Evidence is available that shows that some
episodes of the group of nonspecific symptoms known
as "sick building syndrome" may be related
to microbial contamination in buildings.26
Tuberculosis
The
transmission of airborne infectious diseases is increased
where there is poor indoor air quality.27,28
The rising incidence of tuberculosis is at least in
part a problem associated with crowding and inadequate
ventilation. Evidence is increasing that inadequate
or inappropriately designed ventilation systems in
health care settings or other crowded conditions with
high-risk populations can increase the risk of exposure.29
The incidence of tuberculosis began to rise in the
mid-1980s, after a steady decline. The 1989 increase
of 4.7 percent to a total of 23,495 cases in the United
States was the largest since national reporting of
the disease began in 1953, and the number of cases
has continued to increase each year.30
Fresh air ventilation is an important factor
in contagion control. Such procedures as sputum induction
and collection, bronchoscopy, and aerosolized pentamidine
treatments in persons who may be at risk for tuberculosis
(e.g., AIDS patients) should be carried out in negative
air pressure areas, with air exhausted directly to
the outside and away from intake sources.31
Unfortunately, many health care facilities are not
so equipped. Properly installed and maintained ultraviolet
irradiation, particularly of upper air levels in an
indoor area, is also a useful means of disinfection.32
Legionnaires' Disease
A
disease associated with indoor air contamination is
Legionnaires' Disease,
a pneumonia that primarily attacks exposed people
over 50 years old, especially those who are immunosuppressed,
smoke, or abuse alcohol. Exposure to especially virulent
strains can also cause the disease in other susceptible
populations. The case fatality rate is high, ranging
from five to 25 percent. Erythromycin is the most
effective treatment. The agent, Legionella pneumophila,
has been found in association with cooling systems,
whirlpool baths, humidifiers, food market vegetable
misters, and other sources, including residential
tap water.33
This bacterium or a closely related strain
also causes a self-limited (two- to five-day), flu-like
illness without pneumonia, sometimes called Pontiac
Fever, after a 1968 outbreak in that Michigan city.
Allergic
Reactions
A major concern associated with exposure to biological
pollutants is allergic reactions, which range from
rhinitis, nasal congestion, conjunctival inflammation,
and urticaria to asthma. Notable triggers for these
diseases are allergens derived from house dust mites;
other arthropods, including cockroaches; pets (cats,
dogs, birds, rodents); molds; and protein-containing
furnishings, including feathers, kapok, etc. In occupational
settings, more unusual allergens (e.g., bacterial
enzymes, algae) have caused asthma epidemics. Probably
most proteins of non-human origin can cause asthma
in a subset of any appropriately exposed population.34
The role of mites as a source of house dust allergens
has been known for 20 years34,35.
It is now possible to measure mite allergens in the
environment and IgE antibody levels in patients using
readily available techniques and standardized protocols.
Experts have proposed provisional standards for levels
of mite allergens in dust that lead to sensitization
and symptoms. A risk level where chronic exposure
may cause sensitization is 2 µg Der pI (Dermatophagoides
pteronysinus allergen I) per gram of dust (or 100
mites/g or 0.6 mg quanine/g of dust). A risk level
for acute asthma in mite-allergic individuals is 10
µg (Der pI) of the allergen per gram of dust (or 500
mites/g of dust).
Controlling house dust mite infestation includes covering
mattresses, hot washing of bedding, and removing carpet
from bedrooms. For mite allergic individuals, it is
recommended that home relative humidities be lower
than 45 percent. Mites desiccate in drier air (absolute
humidities below 7 kg). Vacuum cleaning and use of
acaricides can be effective short-term remedial strategies.
One such acaracide, Acarosan, is registered with EPA
to treat carpets, furniture, and beds for dust mites.36
Hypersensitivity Pneumonitis
Another
class of hypersensitivity disease is hypersensitivity
pneumonitis, which may include humidifier fever. Hypersensitivity pneumonitis, also called allergic alveo-litis,
is a granulomatous interstitial lung disease caused
by exposure to airborne antigens. It may affect from
one to five percent or more of a specialized population
exposed to appropriate antigens (e.g., farmers and
farmers' lung, pigeon breeders and pigeon breeders'
disease).37
Continued antigen exposure may lead to end-stage pulmonary
fibrosis. Hypersensitivity pneumonitis is frequently
misdiagnosed as a pneumonia of infectious etiology.
The prevalence of hypersensitivity pneumonitis in
the general population is unknown.
Outbreaks of hypersensitivity pneumonitis in office
buildings have been traced to air conditioning and
humidification systems contaminated with bacteria
and molds.38
In the home, hypersensitivity pneumonitis is often
caused by contaminated humidifiers or by pigeon or
pet bird antigens. The period of sensitization before
a reaction occurs may be as long as months or even
years. Acute symptoms, which occur four to six hours
postexposure and recur on challenge with the offending
agent, include cough, dyspnea, chills, myalgia, fatigue,
and high fever. Nodules and nonspecific infiltrates
may be noted on chest films. The white blood cell
count is elevated, as is specific IgG to the offending
antigen. Hypersensitivity pneumonitis generally responds
to corticosteroids or cessation of exposure (either
keeping symptomatic people out of contaminated environments
or removing the offending agents).
Humidifier Fever
Humidifier fever is a disease of uncertain etiology.39
It shares symptoms with hypersensitivity
pneumonitis, but the high attack rate and short-term
effects may indicate that toxins (e.g., bacterial
endotoxins) are involved. Onset occurs a few hours
after exposure. It is a flu-like illness marked by
fever, headache, chills, myalgia, and malaise but
without prominent pulmonary symptoms. It normally
subsides within 24 hours without residual effects,
and a physician is rarely consulted. Humidifier fever
has been related to exposure to amoebae, bacteria,
and fungi found in humidifier reservoirs, air conditioners,
and aquaria. The attack rate within a workplace may
be quite high, sometimes exceeding 25 percent.
Bacterial and fungal organisms can be emitted from
impeller (cool mist) and ultrasonic humidifiers. Mesophilic
fungi, thermophilic bacteria, and thermophilic actinomycetes-all
of which are associated with development of allergic
responses-have been isolated from humidifiers built
into the forced air heating system as well as separate
console units. Airborne concentrations of microorganisms
are noted during operation and might be quite high
for individuals using ultrasonic or cool mist units.
Drying and chemical disinfection with bleach of 3%
hydrogen peroxide solution are effective remedial
measures over a short period, but cannot be considered
as reliable maintenance. Only rigorous, daily, and
end-of-season cleaning regimens, coupled with disinfection,
have been shown to be effective. Manual cleaning of
contaminated reservoirs can cause exposure to allergens
and pathogens.
Mycotoxins
Another class of agents that may cause disease related
to indoor airborne exposure is the mycotoxins. These
agents are fungal metabolites that have toxic effects
ranging from short-term irritation to immunosupression
and cancer. Virtually all the information related
to diseases caused by mycotoxins concerns ingestion
of contaminated food.40
However, mycotoxins are contained in some kinds of
fungus spores, and these can enter the body through
the respiratory tract. At least one case of neurotoxic
symptoms possibly related to airborne mycotoxin exposure
in a heavily contaminated environment has been reported.41
Skin is another potential route of exposure
to mycotoxins. Toxins of several fungi have caused
cases of severe dermatosis. In view of the serious
nature of the toxic effects reported for mycotoxins,
exposure to mycotoxin-producing agents should be minimized.
References
21
Tom Hoshall's manual for clean air to feel good
23 Burge, Harriet A.
and Feely, J.C. "Indoor Air Pollution and Infectious
Diseases." In: Samet, J.M. and Spengler, J.D.
eds., Indoor Air Pollution, A Health Perspective (Baltimore,
MD: Johns Hopkins University Press, 1991), pp. 273-84.
24 Brunekreeff, B.,
Dockery, D.W. et al. "Home Dampness and Respiratory
Morbidity in Children." American Review of Respiratory
Disease 1989; 140:1363-67.
25 Berstein, R.S.,
Sorenson, W.G. et al. "Exposures to Respirable
Airborne Penicillium from a Contaminated Ventilation
System: Clinical, Environmental, and Epidemiological
Aspects." American Industrial Hygiene Association
Journal 1983; 44:161-69.
26 Burge, Harriet A.
"Bioaerosols: Prevalence and Health Effects in
the Indoor Environment." Journal of Allergy and
Clinical Immunology 1990; 86:687-704.
27 Burge, Harriet A.
"Risks Associated with Indoor Infectious Aerosols."
Toxicology and Industrial Health 1990; 6:263-73.
28 Brundage, J.F.,
Scott, R. et al. "Building-Associated Risk of
Febrile Acute Respiratory Disease in Army Trainees."
Journal of the American Medical Association 1988 259:2108-12.
29 Nolan, C.M., Elarth,
A.M. et al. "An Outbreak of Tuberculosis in a
Shelter for Homeless Men: A Description of Its Evolution
and Control." American Review of Respiratory
Disease 1991; 143:257-61.
30 American Lung Association.
Lung Disease Data 1993. Publication No. 0456, 1993.
31 Centers for Disease
Control and American Thoracic Society. Core Curriculum
on Tuberculosis. Second Edition, 1991.
32 Nardell, E.A., Keegan,
Joann et al. "Airborne Infection: Theroretical
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33 Lee, T.C., Stout,
Janet E. and Yu, V.L. "Factors Predisposing to
Legionella pneumophila Colonization in Residential
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34 Weissman, D.N. and
Schuyler, M.R. "Biological Agents and Allergic
Diseases." In: Samet, J.M. and Spengler, J.D.
eds, Indoor Air Pollution, A Health perspective (Baltimore,
MD: Johns Hopkins University Press, 1991), pp. 285-305.
35 Arlian, L.G. "Biology
and Ecology of House Dust Mite, Dermatophagoides spp.
and Euroglyphus spp." Immunology and Allergy
Clinics of North America 1989; 9:339-56.
36 Platts-Mills, T.A.E.
and Chapman, M.D. "Dust Mites: Immunology, Allergic
Disease, and Environmental Control." Journal
of Allergy and Clinical Immunology 1987;80:755-75.
37 Fink J.N. "Hypersensitivity
Pneumonitis." In: Middleton, E., Reed, D.E. and
Ellis, E.F. eds., Allergy Principles and Practice
(St. Louis:C.V.
Mosby, 19xx), pp. 1085-1100.
38 Fink J.N. "Hypersensitivity
Pneumonitis." In: Middleton, E., Reed, D.E. and
Ellis, E.F. eds., Allergy Principles and Practice
(St. Louis:C.V.
Mosby, 19xx), pp. 1085-1100.
39 Burge, Harriet A.,
Soloman, W.R. and Boise, J.R. "Microbial Prevalence
in Domestic Humidifiers." Applied and Environmental
Microbiology 1980; 39:841-44.
40 Baxter, C.S., Wey,
H.E. and Burg, W.R. "A Prospective Analysis of
the Potential Risk Associated with Inhalation of Aflatoxin-Contaminated
Grain Dusts." Food and Cosmetics Toxicology 1981;19:763-;69.
41 Croft, W.A., Jarvia,
B.B., Yatawara, C.S. 1986. "Airborne outbreak
of trichothecene toxicosis." Atmosph. Environ.
20:549-552. See also Baxter, C.S., Wey, H.E., Burg,
W.E. 1981. A prospective analysis of the potential
risk associated with inhalation of aflatoxin-contaminated
grain dusts. Food Cosmet Toxicol. 19:763-769.
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