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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. References 1. Brown C, Hawkins L. Allergy prevalence and causal factors in the domestic environment: results of a random population survey in the United Kingdom. Ann Allergy Asthma Immunol 1999;83:240-244. 2. Burr M. Epidemiology of asthma. In: Burr M, ed. Epi-demiology of Clinical Allergy. Monographs in Allergy 31. New York, NY: S Karger; 1993; pp 86-102. 3. Cromwell O. What are allergens? Allergy 1999;54 (Suppl 56):7-8. 4. Wilson N, Robinson N, Hogan M. Cockroach and other inhalant allergies in infantile asthma. Ann Allergy Asthma Immunol 1999;83:27-30. 5. Peruzzi M, de Luca M, Novembre E, de Martino M, Vierucci A. Incidence of cockroach allergy in atopic Italian children. Ann Allergy Asthma Immunol 1999;83:167-171. 6. Tunnicliffe W, Fletcher T, Hammond K, Roberts K, Custovic A, Simpson A, et al. Sensitivity and exposure to indoor allergens in adults with differing asthma sever-ity. Eur Respir J 1999;13:654-659. 7. Gergen P, Mortimer K, Eggleston P, Rosenstreich D, Mitchell H, Ownby D, et al. Results of the National Cooperative Inner-City Asthma Study (NCICAS) envi-ronmental intervention to reduce cockroach allergen exposure in inner-city homes. J Allergy Clin Immunol 1999;103:501-506. 8. Sporik R, Squillace S, Ingram J, Rakes G, Hon-singer R, Platts-Mills T. Mice, cat, and cockroach expo-sure, allergen sensitisation, and asthma in children: a case control study of three schools. Thorax 1999;54:675-680. 9. Garcia D, Corbett M, Sublett J, Pollard S, Meiners J, Karibo J, et al. Cockroach allergy in Kentucky: a com-parison of inner city, suburban, and rural small town pop-ulations. Ann Allergy 1994;72:203-207. 10. Kattan M, Mitchell H, Eggleston P, Gergen P, Crain E, Redline S, et al. Characteristics of inner-city chil-dren with asthma: The National Cooperative Inner-City Asthma Study. Pediatr Pulmonol 1997;24:253-262. 11. Whitcomb N. Incidence of positive skin tests among medical students. Ann Allergy 1971;29:67-70. Taksey and Craig • Allergy test results JAOA • Vol 101 • No 5 • Supplement to May 2001 • S7
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Title | Allergy test results of a rural and small-city population compared with those of an urban population |
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Transcript | 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. References 1. Brown C, Hawkins L. Allergy prevalence and causal factors in the domestic environment: results of a random population survey in the United Kingdom. Ann Allergy Asthma Immunol 1999;83:240-244. 2. Burr M. Epidemiology of asthma. In: Burr M, ed. Epi-demiology of Clinical Allergy. Monographs in Allergy 31. New York, NY: S Karger; 1993; pp 86-102. 3. Cromwell O. What are allergens? Allergy 1999;54 (Suppl 56):7-8. 4. Wilson N, Robinson N, Hogan M. Cockroach and other inhalant allergies in infantile asthma. Ann Allergy Asthma Immunol 1999;83:27-30. 5. Peruzzi M, de Luca M, Novembre E, de Martino M, Vierucci A. Incidence of cockroach allergy in atopic Italian children. Ann Allergy Asthma Immunol 1999;83:167-171. 6. Tunnicliffe W, Fletcher T, Hammond K, Roberts K, Custovic A, Simpson A, et al. Sensitivity and exposure to indoor allergens in adults with differing asthma sever-ity. Eur Respir J 1999;13:654-659. 7. Gergen P, Mortimer K, Eggleston P, Rosenstreich D, Mitchell H, Ownby D, et al. Results of the National Cooperative Inner-City Asthma Study (NCICAS) envi-ronmental intervention to reduce cockroach allergen exposure in inner-city homes. J Allergy Clin Immunol 1999;103:501-506. 8. Sporik R, Squillace S, Ingram J, Rakes G, Hon-singer R, Platts-Mills T. Mice, cat, and cockroach expo-sure, allergen sensitisation, and asthma in children: a case control study of three schools. Thorax 1999;54:675-680. 9. Garcia D, Corbett M, Sublett J, Pollard S, Meiners J, Karibo J, et al. Cockroach allergy in Kentucky: a com-parison of inner city, suburban, and rural small town pop-ulations. Ann Allergy 1994;72:203-207. 10. Kattan M, Mitchell H, Eggleston P, Gergen P, Crain E, Redline S, et al. Characteristics of inner-city chil-dren with asthma: The National Cooperative Inner-City Asthma Study. Pediatr Pulmonol 1997;24:253-262. 11. Whitcomb N. Incidence of positive skin tests among medical students. Ann Allergy 1971;29:67-70. Taksey and Craig • Allergy test results JAOA • Vol 101 • No 5 • Supplement to May 2001 • S7 |
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