Allergy test results of a rural and small-city population compared with those of an urban population

              Allergy is a term that indicates an
immediate reaction following con-tact
with a specific environmental anti-gen,
the allergen.1 One of every six per-sons
in the United States suffers from
allergic disease.2 This disease may take
many diverse forms, including rhinitis,
asthma, atopic dermatitis, anaphylax-is,
urticaria, and angioedema.1,2 Allergic
reactions require prior sensitization to
specific antigens.3 Different regions are
associated with different common aller-gens,
and in fact, this distribution is
affected by human activities. For exam-
S4 • JAOA • Vol 101 • No 5 • Supplement to May 2001 Taksey and Craig • Allergy test results
The frequency of sensitization to environmental antigens changes in different
regions. As such, the pattern of sensitivity to common allergens was studied at mul-tiple
sites across central Pennsylvania, an area composed of small cities and rural
communities, to determine uniqueness of allergies in populations from this area in
contrast to allergies as determined by skin testing in large urban centers. The
study reported was undertaken to determine allergen variation from an urban
population compared with a rural population of a Northeastern state so that
environmental avoidance and immunotherapy can be more precisely prescribed.
Patient charts were retrospectively reviewed to determine sensitivity to house dust
mites (Dermatophagoides pteronyssinus, Dermatophagoides farinae), cockroach,
Penicillium, Aspergillus spp, dog, cat, timothy grass, ragweed, oak, and Alternar-ia
tenuis at five sites in Pennsylvania. All of these sites were classified as “small city”
or “rural” for the study. One hundred patient records were examined at each
site for the results of allergy testing by the prick puncture, radioallergosorbent
test (RAST), or intradermal methods. These small-city and rural data were pooled
and compared with that of the National Cooperative Inner-City Asthma Study (NCI-CAS),
which included 1286 patients from urban environments. The prevalence of
allergy to both species of dust mites, dog, timothy grass, and ragweed was signif-icantly
greater in the pooled rural group than in the NCICAS inner-city patients
(P .05). In contrast, sensitivity to cockroach antigens and Alternaria was signif-icantly
greater in the NCICAS urban population than in the pooled rural group
(P .05). No statistically significant difference was found between the NCICAS and
the pooled rural patients in reference to Penicillium, cat, and oak (P .05).
(Key words: allergens, hypersensitivity, allergy, atopic diseases)
Allergy test results of
a rural and small-city
population compared with
those of an urban
population
JASON TAKSEY, MS
TIMOTHY J. CRAIG, DO
Mr Taksey is a student and coinvestigator at
Pennsylvania State University, College of
Medicine, Hershey, Pa. Dr Craig is an associate
professor of medicine and pediatrics and direc-tor
of clinical allergy and asthma research,
Department of Medicine, Division of Pulmonary,
Allergy and Critical Care, Pennsylvania State
University, Hershey Medical Center, Hershey,
Pa.
Correspondence to Timothy J Craig, DO,
Department of Medicine and Pediatrics, Divi-sion
of Pulmonary, Allergy and Critical Care,
Milton S. Hershey Medical Center, 500 Univer-sity
Dr, Hershey, PA 17033-2360.
E-mail: tcraig@psu.edu
ple, allergy to cockroach antigens has
been shown previously to have a high
prevalence in urban areas, especially in
patients of lower socioeconomic sta-tus.
4,5 In contrast, it has been shown to
be less common in suburban and rural
areas because of less infestation of homes
in rural areas, except the Southeast.5
The importance of studying allergic
disease rests in the significant morbidity
that it causes. For example, patients with
severe asthma are more likely to demon-strate
sensitivity to allergens than are
patients with less significant disease.6,7
Studies have shown that by preventing
allergen sensitization through avoidance
techniques, the prevalence of asthma can
be similarly decreased; and, by reduc-ing
the levels of allergen to which a sen-sitized
asthmatic patient is exposed,
symptoms can be improved.7,8 In addi-tion,
immunotherapy has been demon-strated
to be effective.9 Limiting
immunotherapy to the specific allergens
to which the patient is allergic and is
known to be exposed can enhance effect
and decrease cost.
Our study was carried out to review,
in a retrospective fashion, the results of
skin prick, radioallergosorbent test
(RAST), and intradermal allergy tests at
multiple sites across the commonwealth
of Pennsylvania. The purpose of this
undertaking was to determine if a dif-ference
exists in the frequency of sensi-tization
to specific allergens in rural areas
and small cities as compared with large
urban centers.
To gain a more complete under-standing
of the influence of geographic
location on allergic disease, we also com-pared
the results of our study to those of
a similar study performed in Kentucky by
Garcia and colleagues.9 By determining
the common allergens by region, it is
hoped that both diagnostic and treat-ment
modalities can be implemented
more efficiently and effectively, and the
morbidity of hypersensitivity reactions
can thus be reduced.
Methods
Test sites
Five regions in Pennsylvania were cho-sen
from which to acquire rural/small-city
data for the study: Altoona,
Carlisle, Hershey, Forty Fort, and Beth-lehem.
The National Cooperative Inner-
City Asthma Study (NCICAS),7 pub-lished
in 1997, was referenced to
provide a source of inner-city and urban
data.
Data acquisition
At each site, 100 patient records were
reviewed for allergy test results. Of con-cern
were sensitivities to the following
specific allergens: house dust mites (Der-matophagoides
pteronyssinus, Der-matophagoides
farinae), cockroach,
Penicillium spp, Aspergillus spp, dog,
cat, timothy grass, ragweed, oak, and
Alternaria tenuis.
Prick puncture, intradermal, and
rarely in vitro tests for specific IgE were
included.
Taksey and Craig • Allergy test results JAOA • Vol 101 • No 5 • Supplement to May 2001 • S5
Table
Percentage of Patients With Positive Allergy Test Results by Location
Patients with positive test results, %
Rural All
Forty pooled pooled
Allergen Bethlehem Carlisle Fort Altoona Hershey data NCICAS* data
  Mites (Df)† 52 27 50 50 43 44 24 30
  Mites (Dp)‡ 53 24 50 50 42 44 31 35
  Cockroach 44 7 ND§ 12 16 20 36 32
  Penicillium 31 8 8 22 12 16 20 19
  Aspergillus spp 34 10 14 33 7 20 ND§ 20
  Dog 46 15 37 38 13 30 16 20
  Cat 38 20 28 47 28 32 24 26
  Timothy 37 26 49 36 27 35 21 25
  Ragweed 53 23 34 33 33 35 17 22
  Oak 43 16 22 25 26 26 23 24
  Alternaria tenuis 36 17 17 32 17 24 38 34
* NCICAS   National Cooperative Inner-City Asthma Study.
† Df  Dermatophagoides farinae.
‡ Dp  Dermatophagoides pteronyssinus.
§ ND   not done.
Data analysis
The five rural/small-city sites were pooled
into one data set for all 11 allergens test-ed.
This pooled data set was then com-pared
with that of the NCICAS by use of
2   2  2 tests for each allergen.
Results
Patients
A total of 500 patients were included in
the study to represent the rural/small-city
group. The NCICAS, which was
used for urban data, included 1286 sub-jects.
The Table compares the frequencies
of positive test results at each site,
between urban and rural sites (pooled
rural data), and all data pooled, which
represents sensitization in the general
population of the Northeast.
Pooled data
We compared the NCICAS urban data
with data of a group consisting of all
the rural/small-city sites pooled (Table).
The following results were found. The
prevalence of allergy to both species of
dust mites, dog, timothy grass, and rag-weed
was significantly greater in the
pooled rural group than in the NCICAS
inner-city patients (P .05). In contrast,
sensitivity to cockroach antigens and
Alternaria was significantly greater in
the NCICAS urban population than in
the pooled rural group (P .05). No sta-tistically
significant difference was found
between the NCICAS and the pooled
rural patients in reference to Penicilli-um,
cat, and oak (P>.05).
Discussion
Our study was performed to determine
if a difference in the frequency of allergen
sensitization exists between rural
regions/small cities and large metropoli-tan
areas. Past research has shown that
cockroach allergy is more common in
urban settings.4,5 In designing this study,
we hoped to clarify similar patterns for
other allergens.
Based on the comparison between
the pooled rural data and the NCICAS
data, our study found that allergy to
dust mites, dog, timothy grass, and rag-weed
is more common in rural areas/
small cites than in large metropolitan
centers. In contrast, cockroach and
Alternaria hypersensitivity was shown
to be more prevalent in large cities. These
findings suggest that a regional differ-ence
does exist in reference to common
allergens to which patients are sensitized,
even within a similar climatic condition.
This conclusion is further supported
by the results of a study by Garcia and
associates.9 They looked at the preva-lence
of cockroach allergy in inner-city,
suburban, and rural/small-town Ken-tucky.
In their study, they reported that
overall, 41% of inner-city patients,
30.1% of suburban patients, and 43.6%
of rural/small-town patients demon-strated
sensitivity to cockroach antigens.
A statistically significant difference was
found between the inner-city and sub-urban
populations and between the
rural/small-town and suburban groups.
However, no significant difference in the
prevalence of cockroach allergy was
found when inner-city patients were com-pared
with rural/small-town patients.
These results differ from those of our
study in which cockroach hypersensitiv-ity
was found to be significantly more
common in large cities than in rural areas.
As mentioned previously, cockroach aller-gy
has been previously found to be more
common in cities than in less urban
regions.4,5 Our study confirms that this is
the case in a northern state. Despite this
confirmation, we were impressed with
the frequency of cockroach allergy in
small cities and rural areas of the North-east.
Cockroaches are thought to be an
infrequent inhabitant of single-family
houses in the North. The frequency of
positive reactions may reflect cross-reac-tivity
to other insect exposures. Reloca-tion
from areas where cockroaches are
more common may account for a portion
of the positive tests in central Pennsyl-vania;
however, the population of central
Pennsylvania is very stable.
In previous studies, up to 50% to 60%
of patients have demonstrated an aller-gy
to house dust mites.10 Similar num-bers
were found in this study, with the
exception of the Carlisle test site and the
NCICAS (Table). Of importance, allergy
to both species of mites in the NCICAS
inner-city patients was found to be sig-nificantly
lower than in the pooled rural
group. This would seem to indicate that
in contrast to cockroach allergy, hyper-sensitivity
to house dust mites is not as
prevalent in cities as in less urban areas.
The almost identical sensitivities between
the two house dust mites in the population
we studied again confirms cross-reactivi-ty
of the dust mites D farinae and D
pteronyssinus (Table). This cross-reactiv-ity
suggests that including only one of the
two species in the RAST and skin test
panels and treatment sets is adequate. We
were unable to explain the difference
between sensitivities to D farinae and D
pteronyssinus in the NCICAS.
Penicillium, an indoor mold, would
be expected to have a uniform preva-lence.
Our study found this expectation
to be broadly true in that there was not
a statistically significant difference in the
frequency of sensitization in rural regions
as compared with the NCICAS data.
Because the NCICAS did not study
Aspergillus, it cannot be determined from
our study if any differences exist between
its prevalence in urban and rural/small-city
environments. Because Aspergillus is
an indoor mold, we would expect simi-lar
prevalence of positive sensitivities. In
our population, skin test positivity to
Aspergillus and Penicillium is similar, as
expected, as both are indoor molds.
Sensitivity to pets—dogs and cats—
varies from site to site. Pooled data for
small-city/rural areas demonstrated that
dogs were responsible for greater rates
of sensitivity in these areas as compared
with large urban regions. However, rates
of sensitivity to cat was not significantly
different in rural/small-city areas as com-pared
with that in large urban centers.
Allergy to timothy grass is distinct
between urban and rural/small-city sites.
There was a statistically significant differ-ence
between the NCICAS inner-city group
and the pooled rural group. However, it is
difficult to interpret this data set because the
NCICAS tested mixed grass, not specifically
timothy. Nevertheless, most northern grass-es
cross-react, and thus, a comparison of
timothy grass with a mixed grass is prob-
S6 • JAOA • Vol 101 • No 5 • Supplement to May 2001 Taksey and Craig • Allergy test results
ably a legitimate one and suggests decreased
exposure to grasses in an urban setting, a
not unexpected difference.
Similar to grasses, a difference in the
prevalence of ragweed allergy exists
between urban and rural/small-city groups.
The NCICAS inner-city patients demon-strated
a significantly lower level of rag-weed
sensitization than the pooled rural
group. Again, this finding probably reflects
increased exposure in rural regions, because
ragweed grows in areas of tilled soil.
For oak, unlike the other plants, our
study does not show convincing evidence
that the prevalence of oak allergy varies
from rural to urban regions. The lack
of difference in oak allergy, as compared
with grasses and ragweed allergy, prob-ably
is secondary to the planting of oak
trees in metropolitan centers along streets
and in parks. Oak trees are frequently
used, even though they are not the pre-ferred
trees for city planting. Other expla-nations
for the uniform sensitivity to
oak are the prolific production of pollen
from trees, the large distribution of oak
tree species throughout the United States,
and the large distance that tree pollen
can be distributed by the wind.
As expected, the prevalence of
Alternaria allergy does vary between
regions. The presence of Alternaria and
thus allergy to it are expected to be high-est
in agricultural regions; however, in
our study, the NCICAS inner-city
patients demonstrated a significantly
greater frequency of Alternaria sensitiv-ity
than the pooled rural group. This
prevalence of Alternaria sensitivity in
cities over that in smaller communities
and rural areas is surprising and con-trary
to the belief that Alternaria is most
prevalent in areas of farms and grass-lands.
From the analysis of the study data
pooled, the most common allergens to
which patients are sensitized in the
Northeast region of the country as a
whole can be determined and used as a
standard for this broad area. In our
study, dust mites, Alternaria, and cock-roach
showed the greatest prevalence in
the pooled patient population (Table).
Pollen and cat sensitivity were common,
but less so (Table). Indoor molds and
dog allergy demonstrated the lowest
prevalence in our study (Table). A sim-ilar
study was performed by Whitcomb
in 1971.11 In his research, he found that
mixed-grass pollen and house dust aller-gy
were most prevalent. Although he
did not study dust mites specifically, they
are a significant allergic component of
house dust. Alternaria and cat hyper-sensitivity
were among the next most
common. Similar to the pooled patient
population in our study, dog allergy was
less prevalent than cat allergy. Whit-comb
did not study cockroach, or any of
the other molds included in our study.
Several factors may account for the dif-ference
between his and our work, but
the most significant is that his study was
performed in California. In addition, it is
possible that allergen prevalence changes
over time as buildings vary in design and
urbanization continues to spread. This
possibility reaffirms the need to deter-mine
the common allergens in a region
for the implementation of efficacious
treatment of allergic disease.
Certain limitations are associated with
the data presented in our study. The first
is that migration of patients to their spe-cific
region from other areas could not be
controlled. For example, subjects from
the Hershey rural test site could actual-ly
be from Harrisburg, an urban area.
Their allergen sensitivities would thus
not be representative of Hershey, pro-ducing
some inaccurate results. Testing
between sites varies. Sites may have a
different criterion to determine positive
and negative test results. In addition,
techniques, allergens, and frequency of
intradermal test use may vary. Despite
these limitations, however, our study
reflects a real-life situation in which pop-ulations
shift regularly and techniques
used by allergists vary significantly.
Comment
Based on the results of our study, we
conclude that allergies to cockroach and
Alternaria are more common in large
cities than in rural areas and small cities.
We also reaffirm that sensitivity to dust
mites, ragweed, and timothy grass is
more prevalent in rural areas and small
cities than in inner-city areas. Our find-ings
confirm the data presented by the
NCICAS for cockroach, but it is con-trary
to that expected for Alternaria.
This information is useful for determin-ing
the makeup of standard allergy pan-els
based on geographic location. Patients
in urban and rural areas should be test-ed
for cockroach allergy. Alternaria is
expected in farming communities, but
it also is important to incorporate it into
panels used in metropolitan areas.
Whereas the most common allergen to
cause a positive skin test is house dust
mite in small cities and rural areas,
Alternaria and cockroach are the most
common allergens in inner cities.
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