United States
Environmental Protection
Agency
»EPA
Off ice Of
The Administrator
(A101F)
EPA171-R-92-016
PB-92-182419
1992
A Study Of
House Dust
Mites And Cat Dander
In The Office Enviroment
Printed on Recycled Paper
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A Study of House Dust Mites
and Cat Dander in
The Office Environment
Stacey J. Baker
Francis Dougherty (Project Officer)
August 28,1991
U.Si Enyirofcmentai Protection
Pcni'tfa 5, Library (PL-12J)
••7\V^t JacksC'3 Bcu!-, .% j
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DISCLAIMER
This report was furnished to the U.S. Environmental Protection
Agency by the student identified on the cover page, under a National
Network for Environmental Management Studies fellowship.
The contents are essentially as received from the author. The
opinions, findings, and conclusions expressed are those of the author
and not necessarily those of the U.S. Environmental Protection
Agency. Mention, if any, of company, process, or product names is
not to be considered as an endorsement by the U.S. Environmental
Protection Agency.
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This paper is the result of a joint project between the United States
Environmental Protection Agency and the United States Public Health Service and
will become part of a future journal article. Individuals who took part in the project
and writing of this paper are as follows:
United States Environmental Protection Agency:
Stacey Jill Baker
Francis Dougherty
United States Public Health Service
Chin S. Yang, Ph.D.
Ling Ling Hung, Ph.D.
Frank Lewis
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Literature Review
House dust mites and cat dander have both been known to induce allergic
responses and asthmatic attacks in many individuals. Many researchers have
conducted studies which concern these allergens in the home; however, few studies
have assessed the "working" or "office" environment in the United States. As a
result, this study concentrates on the presence of house dust mites and cat dander in
large office buildings in the eastern United States-
There are two species of Dermatophagoides that are most commonly found
in the home and are frequent sources of house dust allergy: Dermatophagoides
pteronyssinus and D. farinae (1-19). As their name indicates, the main diet of these
microscopic organisms is human skin scales; hence, they are frequently found in
"high use areas" where there is a great deal of human presence and activity (2, 6,8-
12,20,21). In addition to the above nutritional requirement, the Dermatophagoides
spp. also require proper humidity and temperature for survival and maintenance of
homeostasis.
Former studies have stated that humidity is a key factor in controlling mite
breeding and numbers (2,4-6,8-14,18,20,22,23-32). Although humidity is difficult to
control (6), it remains a crucial tool for controlling mite populations. The
microenvironment of these mites contains no liquid water (12); if an absolute
indoor humidity of 7g/kg (2,6,8) (equivalent to a relative humidity of 60% at 70°F)
(2) is not maintained, water loss and subsequent dehydration can occur. The use of
air-conditioners not only lowers room temperatures, but also the indoor humidity
by removing water form the air (6,8). Thus, areas that are air-conditioned generally
harbor fewer mites than those areas without an air-conditioning system; in one
study, mite numbers were reduced by a factor of ten (33). (This is not to say,
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however, that mite allergen levels will drop with the use of air-conditioning if mite
feces is present in the environment). Due to the fact that humidity is so important
for mite survival, mite growth has been correlated with seasonal variations in
temperate regions around the world (5,6,8,10,12,21,24,25,30); for example, in North
America, mite growth has reached maximum levels in the summer months when
the humidity is the highest (2,26).
As aforementioned, temperature is another important factor in maintaining
house dust mite populations. Temperatures that are either too high or too low can
affect mites. The life cycle from egg to adult for both D. pteronyssinus and D. farinae
is approximately 23-30 days; the duration of this cycle can be shortened by higher and
lengthened by lower temperatures (12). Optimal temperature for growth is within
the range of 17-25°C (25). Environmental conditions, humidity in particular, also
influence the particular species of mite that dominates in the home to some degree.
Homes with lower indoor humidity usually contain predominantly D. farinae
whereas it appears that D. pteronyssinus requires higher humidity for survival (1-3,
6,12,18,2432).
In addition to the climate of the actual room, the microclimate which is
provided by carpets and upholstery of furniture is also important. Long pile carpets
contain more mites than short pile carpets, and the latter contain more than un-
carpeted (tile of wood) floors. Apparently, long pile carpets are able to accumulate
and maintain adequate food supplies as well as adequate climactic conditions
needed to sustain a mite population (10,12,22). It is also important to note that
vacuuming of long pile carpets does not allow full removal of mite bodies and feces
that are present. Vacuuming merely removes a fraction of what is present,
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Allergens from
particularly the surface dust, as has been determined by studies that yielded equal
amounts of dust and .llergens after repeated vacuumings (8,10,12,28).
the Dermatophagoides species of mite are classified into two
groups: Group I (Der J> I and Der f I) and Group U (Der p H and Der f H) allergens.
The first purified grout) of allergens, Group I, have a molecular weight of 25,000 and
are characterized as glycoproteins (2,25). Both Der p I ( a cysteine protease) (34) and
Der f I display cross reactivity, structural homology, and are associated with mite
feces that are carried 01 pa-tides greater than 10 um in diameter (2,6-8,25,35). Due to
their large size, the amount of airborne allergen is small (immeasurable in some
studies) unless the roo n is disturbed; in this particular case, allergen (and particle)
levels rise with disturb
making), and then fall
fall within a five minu
house dust mites may
(36). The Group II alle
with the whole body oi
ance (i.e. human activities such as vacuuming and bed-
quickly. Certain studies have shown that these large particles
:e time period. Hence, many individuals who are allergic to
only experience symptoms upon entering a disturbed room
•gens have a molecular weight of 15,000 and also display dose
structural homology and cross-reactivity (25). Der p H and Der f H are associated
the mite (7); in addition, a study conducted by Sakaguchi et.
al. (7) has suggested th^t Der H allergens are less prone to float that the Der I
allergens.
Unlike the allergens of the above mentioned house dust mites, the major cat
allergen, Pel d I, tends :o remain airborne for longer periods of time with or without
disturbance due to the :act that this particular allergen is carried on partides less
than 2.5 um in diamet jr. Hence, while those individuals who are sensitive to
house dust mites may Experience little discomfort in an undisturbed setting, those
who are allergic to cats Lay experience a rapid onset of asthmatic and allergic
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symptoms in an identical undisturbed environment. Even after disturbance, these
smaller particles can remain airborne for many hours (35).
Pel d I, with a molecular weight of 37,000 is characterized as an acidic salivary
protein; thus, the main source of this allergen is probably saliva. Nevertheless,
further crossed radio-immunoelectrophoresis (CRIE) analysis shows that Pel d I is a
dander (superficial skin material) related component. It is also important to note
that cat hair has been used to obtain the most complete cat allergen extract (37). Due
to the fact that most cats shed quite often, the feline does not have to be present in
order to induce an allergic response. It is a reasonable assumption that those
individuals who own a cat serve as carriers for the allergen throughout areas where
a cat has not been found.
In conclusion, allergies to common house dust are common due to the
numerous amount of allergens that are carried on dust particles. Both
Dermatophagoides spp. and cat allergens have been identified as major allergens.
Due to the high number of individuals who are allergic to the substances, a study
involving their role in the office building environment is considered.
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Introduction
House dust mites and cat dander have both been known to induce asthmatic
attacks and allergic responses in many individuals . There have been many studies
regarding the major allergens from house dust mites and cats in the homed-3,5-
8,13,24-26,34-37,39-41); however, few studies have been conducted regarding these
allergens in the office environment. This study surveys the presence of house dust
mites and cat dander in large office buildings.
Materials and Methods
Five office buildings (two located in Philadelphia, Pennsylvania; three located
in Washington D.C.) were visited during the first two weeks of August; each
building was selected on the basis of previously obtained indoor air information and
accessibility.
Ten sites were randomly chosen in each building and sampled in the
following manner: approximately, a square meter area of carpet was vacuumed with
a vacuum cleaner (Hoover Legacy, model 810) for one minute ( to avoid extreme
noise disturbance in a working office environment) with the aid if an indoor
allergen collection device supplied by ALK laboratories. This device fits onto the
hose of a conventional vacuum. Temperature, relative humidity, and carbon
dioxide were also measured at the time of collection. At five of the ten sites in each
building, the entire surface area of an upholstered chair was sampled in addition to
the carpet (bringing the total number of samples in each building to fifteen). In
addition to the above, a questionnaire was distributed to approximately five
individuals at each sampling site. (A sample copy is attached).
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All samples were kept in their original collection containers and sealed in
food storage bags until the final analysis (performed 1-2 weeks after collection).
The samples were sent to ALK laboratories for immunochemical analysis which
measured the concentrations of house dust mite and cat allergens: Der p I, Der f I,
and Pel d I by the ELISA method.
The questionnaires used in this study were tabulated. Information such as
the percentage of individuals who are allergic to dust mites and cat dander, and the
percentage of individuals who own cats was obtained.
Results and Discussion
A total of 75 samples and 211 questionnaires were collected from 50 sites in 5
office buildings. Although the total laboratory data has not yet become available,
statistical results were obtained from the questionnaires (Table 1). The table shows
the number and percentage of individuals in each building who are allergic to
house dust mites and cat dander; the number and percentage of individuals who
may be allergic to cat dander; the number and percentage of individuals who own
cats; and the total number of cats.
When the individual numbers and percentages are combined, the study
reveals that 16.11% of the individuals have been diagnosed as being allergic to
house dust mites and that 8.05% of the individuals have been diagnosed as being
allergic to cat dander. However, twenty-five of the questioned individuals feel that
they are possibly allergic to cat dander; if these individuals are included, the
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8
percentage of individuals allergic to cat dander increases to almost 20%. Hence,
according to this study, 1 out of 5 individuals is potentially allergic to cat dander.
It has been stated in a previous study conducted by Luczynska et. al. (35) that
28% of American homes own at least one cat. The numbers generated by this
particular study show that 21.3%, or approximately one out of every five individuals
owns a cat. Hence, according to this preliminary study, roughly equal percentages of
the population own a cat or are allergic to cat dander.
The portion of laboratory data which has become available is shown on tables
2-6. It is important to note the areas which contain moderate to high concentrations
of allergens; all but one of these areas contain no questioned individuals who spoke
of allergic reactions in the working environment. Guidelines concerning levels of
Der p I, Der f I, and Pel d I are as follows (21,38-40):
Per p I and Per f I
Less than 2ug/g dust LOW
2 to lOug/g dust MODERATE (risk of development of asthma)
(2ug/g equals approximately
100 mites/g dust)
Greater than lOug/g dust HIGH (risk for acute asthmatic attack)
(lOug/g equals approximately
500 mites/g dust)
Pel d I
Less than lug/g dust LOW
1 to 8 ug/g dust MODERATE (may be risk factor for sensitization
to cats)
Greater than 8 ug/g dust HIGH (risk factor for acute asthma)
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It has been previously stated that humidity is a crucial tool which controls mite
populations; in addition, by removing water from the air, air-conditioning has been
known to reduce mite populations. All of the areas sampled in this study are air-
conditioned. Although microscopic counts have not yet been performed, it is
thought that the air-conditioning may have controlled mite numbers in areas
where little or no mite allergen was found. Obviously, further laboratory analysis is
needed to confirm this possible conclusion.
Optimal growth conditions for house dust mites is 70°F with a relative
humidity of 70% (2). None of the areas whose data has been made available had a
relative humidity greater than 66%. However, as the tables show, many areas have
temperatures at or greater than 70°F, relatively suitable for mites.
None of the 50 sampled sites whose laboratory data is available contained
high concentrations of Der p I allergen. However, two of the sites did contain high
levels of Der f I. The questionnaires from these areas showed that two individuals
were diagnosed as being allergic to house dust mites. In fact, one individual in one
of these areas complained of allergic responses in the working environment. These
responses may indicate that house dust mites may be present in offices and able to
induce allergic symptoms. Further studies are needed to test the validity of this
statement.
There were four sites which had high concentrations of Pel d I: 11.4 ug/g,
13.8 ug/g, 16.7 ug/g, and 30.7ug/g. The number of cats whose allergens could
potentially be carried into these office areas are: 0,8,7,and 1 respectively. These
results may show, like those of previous studies (41), that the cat need not be present
for cat allergens to appear in the environment. This phenomenon is due to the fact
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10
that cat allergens are carried on dust particles less that 2.5 urn in diameter (35,36);
these particles float easily and may be carried by humans into other areas.
The above are the preliminary results of this study regarding house dust
mites and cat dander in the office environment. Further studies are needed to
substantiate the data generated from this study.
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Table 1
Building
Building 1
Building 2
Building 3
Building 4
Building 5
Individuals
Questioned
43
49
39
35
45
Dust Mite
Allergic
Individuals
9
8
5
2
10
% Allergic
to Dust
Mites
20.9
16.32
12.8
5.71
22.2
Cat Dander
Allergic
Individuals
3
5
3
1
5
% Allergic
to Cat
Dander
6.9
10.2
7.69
2.85
11.11
Individuals
Who May Be
Allergic to
Cat Dander
9
8
4
4
3
% May Be
Allergic
to Cat
Dander
20.93
16.32
23.07
11.42
6.66
Individuals
with Cats
1 2
9
9
1 2
3
% With
Cats
27.9
18.36
23.07
34.28
6.66
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Table 2- Building 1
Sample Der pi Der f I Pel d T rr* T
rei d i C02 Temperature Relative
(ppm) (Fahrenheit) Humidity
01
02
03
04
05
06
07
08
09
1 0
1 1
12
13
14
15
0-1 0.1 0.9 450
0.2 0.4 6.1 450
O.Ob O.Ob 30.7 550
0-1 O.Ob 1.1 450
O.Ob O.Ob 0.7 450
* * 500
550
O-1 0.5 16.7 500
500
* * *
* 450
0.1 6.9 0.1 450
°-1 15.4 O.Ob 400
°-0b 0.6 O.Ob 450
O.Ob 0.2 0.7 450
O.Ob 0.1 0.2 350
76
76
74
72
72
77
78
77
78
72
72
73
72
72
75
38
38
48
46
46
39
48
' 39
39
50
50
48
48
48
40
* Data not yet available
b Below detection limit
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Table 3- Building 2
Sample Der p I Der f I Fel d I
CO2 Temperature Relative
(ppm) (Fahrenheit) Humidity
01
02
03
04
05
06
07
08
09
10
1 1
12
13
14
15
* * *
O.Ob 0.3 0.4
* * *
0.1 0.1 1.4
* * *
* * *
* * *
0.1 0.4 0.4
0.1 O.Ob 0.1
* * *
O.Ob 0.1 13.8
* * *
* * *
* * *
0.1 0.3 11.4
550
550
450
450
500
500
550
550
500
600
600
550
450
650
650
77
77
75
75
74
75
78
78
79
77
77
76.5
72.5
69
69
48
48
47
47
50
47
48
48
50
45
45
45
47
50
50
* Data not yet available
b Below detection limit
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Table 4- Building 3
Sample Der p I Der f I Pel rf T rrv. T
F i rei d I O02 Temperature Relative
(ppm) (Fahrenheit) Humidity
01
02
03
04
05
06
07
08
09
10
1 1
12
13
14
15
550
600
600
350
°-1 O.Ob O.Ob 450
°-6 0.5 0.3 450
* * *
* 600
* * *
* 400
°'1 0.1 0.2 500
°'6 1-5 1.0 500
°'1 2.5 0.3 500
°-6 2.9 0.7 500
* * *
* 450
0-7 3.0 0.4 450
0.2 4.6 0.2 550
73
74
74
72
72
72
72.5
71
73
73
76
76
72.5
72.5
72
57
54
54
60
57
57
57
61
46
46
42
42
47
47
52
* Data not yet available
b Below detection limit
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Table 5- Building 4
Sample Der p I Der f I Pel d I
C02 Temperature Relative
(ppm) (Fahrenheit) Humidity
01
02
03
04
05
06
07
08
09
10
1 1
12
13
14
15
*
2.4
*
*
0.7
*
*
0.1
0.1
*
0.1
*
0.1
O.Ob
*
*
0.7
*
*
0.5
*
*
2.1
0.5
*
0.4
*
0.4
0.1
*
*
7.3
*
*
0.5
*
*
2.4
O.Ob
*
0.8
*
0.3
0.5
*
350
350
300
400
400
350
350
350
400
400
400
400
400
350
300
71
71
72
70,5
70.5
74
71
71
73.5
73
73
76
76
74
67.5
64
64
60
60
64
64
64
64
57
59
59
54
54
54
64
* Data not yet available
b Below detection limit
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Table 6- Building 5
Sample Der pi Der f I Pel d I rrv, T,
™ a i UJ2 Temperature Relative
(ppm) (Fahrenheit) Humidity
01
02
03
04
05
06
07
08
09
10
1 1
12
13
14
15
* * *
* 350
0.1 0.1 0.2 350
* * *
* 550
* * *
* 550
°-0b 0-3 0.1 600
°'2 1-2 0.4 600
* * *
* 550
°'4 0-3 0.7 550
O.Ob 6.8 0.3 550
* * *
* 550
* * *
* 550
* * *
* 550
°-0b 1-7 O.Ob 600
°'1 1-3 0.2 600
* * *
* 350
67
67
70.5
70
70
70
70.5
70.5
67
67
71
70
71.5
71.5
71
57
57
58
60
60
60
55
'55
55
55
56
51
50
50
52
* Data not yet available
b Below detection limit
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