The prevalence of allergic sensitization has increased in most developed counties over the past century. In the United States, the third National Health and Nutrition Examination Survey1x1Arbes, S.J. Jr., Gergen, P.J., Elliott, L., and Zeldin, D.C. Prevalences of positive skin test responses to 10 common allergens in the US population: results from the third National Health and Nutrition Examination Survey. J Allergy Clin Immunol. 2005;
116: 377–383
Abstract | Full Text | Full Text PDF | PubMed | Scopus (456) | Google ScholarSee all References found 54.3% of the study population to have evidence of allergic sensitization. European studies2x2Weinmayr, G., Genuneit, J., Nagel, G., Bjorksten, B., van Hage, M., Priftanji, A. et al. International variations in associations of allergic markers and diseases in children: ISAAC Phase Two. Allergy. 2010;
65: 766–775
Crossref | PubMed | Scopus (34) | Google ScholarSee all References have shown similar findings. In contrast to these studies of increasing prevalence, there are now a number of studies demonstrating that certain populations have a significantly lower prevalence of allergic sensitization and a lower prevalence of asthma.3x3von Mutius, E. and Vercelli, D. Farm living: effects on childhood asthma and allergy. Nat Rev Immunol. 2010;
10: 861–868
Crossref | PubMed | Scopus (353) | Google ScholarSee all References Children who reside on traditional Swiss farms are among those with a low prevalence of allergic sensitization.4x4Riedler, J., Braun-Fahrlander, C., Eder, W., Schreuer, M., Waser, M., Maisch, S. et al. Exposure to farming in early life and development of asthma and allergy: a cross-sectional survey. Lancet. 2001;
358: 1129–1133
Abstract | Full Text | Full Text PDF | PubMed | Scopus (1026) | Google ScholarSee all References
We sought to compare the prevalence of allergic sensitization in a population of Amish children aged 6 to 12 years with both children living on farms in Switzerland and nonfarm Swiss children. The Amish dispersed from Switzerland approximately 200 years ago seeking freedom from religious persecution. Although the Amish can be found in a number of countries and various communities in America, the largest concentrations are found in Pennsylvania, Ohio, and Indiana. In Indiana, there are approximately 25,000 members in their community. They live primarily an agrarian lifestyle. Many families live on working farms. All Amish families have horses that are used for transportation. A significant percentage drinks raw milk. They do not use electricity in their homes. They have large families.
In Switzerland, 28,686 questionnaires were distributed to families of children aged 6 to 12 years in phase 1 of the GABRIEL study (2006-2007). The GABRIEL questionnaire assessed demographic characteristics, contact to farming environment, symptoms and reported diagnoses of asthma, hay fever, and atopic dermatitis as well as parental smoking (Table ITable I).5x5Genuneit, J., Büchele, G., Waser, M., Kovacs, K., Debinska, A., Boznanski, A. et al. The GABRIEL Advanced Surveys: study design, participation and evaluation of bias. Paediatr Perinat Epidemiol. 2011;
25: 436–447
Crossref | PubMed | Scopus (35) | Google ScholarSee all References A stratified random sample of consenting children was invited to assess serum-specific IgE to inhalant and food allergens. Atopy was defined as any positive IgE level of 0.7 kU/L or more. For the Amish study, permission was obtained from the Amish School Board to distribute questionnaires in 7 schools from different church districts for an unbiased sample selection of children aged 6 to 12 years. A total of 185 questionnaires were distributed, of which 157 were returned. Of these, 138 children participated in skin prick testing after parental consent. Among the Amish, a slightly modified GABRIEL phase 1 questionnaire was distributed in December 2010. Consenting children were invited for a skin prick test session in March 2011. Skin prick testing was done by using a Duotip-Test (Lincoln Diagnostics, Decatur, Ill) to similar although not identical inhalant allergens (ALK-Abelló, Round Rock, Tex). A positive skin prick test result was a wheal greater than or equal to 3 mm after subtraction of the negative control.
Table ICharacteristics and farm exposures of the study population | n (%) |
|---|
| Amish (n = 157) | Swiss farmer (n = 3,006) | Swiss nonfarmer (n = 10,912) |
|---|
| Female sex | 61 (39.9) | 1,542 (51.3) | 5,263 (48.3) |
| Age (y), mean ± SD | 10.1 ± 1.70 | 9.9 ± 1.89 | 9.9 ± 1.88 |
| No. of children, mean ± SD∗ | 5.9 ± 2.25 | 3.3 ± 1.27 | 2.4 ± 0.94 |
| Maternal smoking†† |
| Never | 64 (92.8) | 1,567 (79.3) | 5,171 (62.6) |
| Ex-smoker | 0 | 240 (12.1) | 1685 (20.4) |
| Current | 5 (7.2) | 170 (8.6) | 1,398 (16.9) |
| Parents or siblings affected by |
| Asthma | 8 (5.2) | 451 (15.2) | 2,064 (19.1) |
| Hay fever | 24 (15.4) | 559 (18.8) | 4,127 (38.3) |
| Atopic dermatitis | 10 (6.4) | 482 (16.3) | 2,078 (19.3) |
| Family lives on a farm†† | 61 (84.7) | 2,024 (100.0) | |
| Child regularly spent time in a barn | 143 (91.7) | 2,735 (91.8) | |
| Child regularly drank milk directly from a farm | 124 (79.5) | 2,614 (87.2) | |
| Type of animal farming†† |
| Dairy | 17 (23.6) | 1,322 (66.9) | |
| Cow/cattle | 34 (47.2) | 1,158 (58.6) | |
| Pig | 10 (13.9) | 640 (32.4) | |
| Sheep | 7 (9.7) | 328 (16.6) | |
| Poultry | 34 (47.2) | 690 (34.9) | |
| Horse | 55 (76.4) | 373 (18.9) | |
| Goat | 9 (12.5) | 358 (18.1) | |
| Bunny/rabbit | 17 (23.6) | 718 (36.3) | |
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In Switzerland, 65% returned questionnaires; 89% of the subsample had IgE level measurements. Among the Amish, 85% returned questionnaires and 75% participated in skin prick testing. Based on parental reporting, the prevalence of ever having asthma was 5.2%, 6.8%, and 11.3% among Amish, Swiss farm, and Swiss nonfarm children, respectively. The corresponding figures for allergic sensitization were 7.2%, 25.2%, and 44.2%. Dust mite sensitization figures were 5.8%, 9.3%, and 16.4% respectively. Sensitization to mixed grasses was 2.9%, 20.1%, and 39.8% among Amish, Swiss farm, and Swiss nonfarm children.
Sex and age distribution was similar in all study groups. Amish children and those living on a Swiss farm drink milk directly from the farm (79.5% and 87.2%, respectively). More than 90% of the Amish and Swiss farm children regularly spent time in barns. As part of the definition, none of the Swiss nonfarm children drank unprocessed milk directly from the farm or had regular contact with farm animals. The mean number of children per family was 5.9 among the Amish, 3.3 among the Swiss farm families, and 2.4 among the Swiss nonfarm families (Table IITable II).
Table IIAsthma and allergic disease | n (%) |
|---|
| Amish (n = 157) | Swiss farmer (n = 3,006) | Swiss nonfarmer (n = 10,912) |
|---|
| Wheeze (past 12 mo) | 6 (3.9) | 156 (5.3) | 1,020 (9.5) |
| Doctor diagnosis of asthma∗ | 8 (5.2) | 202 (6.8) | 1,218 (11.2) |
| Doctor diagnosis of bronchitis†† | 22 (14.3) | 504 (17.7) | 2,445 (24.1) |
| Doctor diagnosis of croup†† | 22 (14.1) | 320 (11.4) | 1,545 (15.6) |
| Inhaler (ever) | 8 (5.1) | 265 (8.9) | 1,494 (13.8) |
| Rhinoconjunctivitis (past 12 mo) | 8 (5.2) | 143 (4.8) | 1,412 (13.0) |
| Doctor diagnosis of hay fever (ever) | 1 (0.6) | 94 (3.1) | 1,259 (11.6) |
| Doctor diagnosis of atopic eczema (ever) | 2 (1.3) | 226 (7.6) | 1,310 (12.1) |
| Atopy‡‡ | 10 (7.2) | 223 (25.2) | 281 (44.2) |
| Dematophagoides pteronyssinus, ‖ | 8 (5.8) | 82 (9.3) | 102 (16.4) |
| Cat, ‖ | 1 (0.7) | 32 (3.6) | 66 (10.6) |
| Birch‖‖ | | 71 (8.0) | 122 (19.6) |
| Mixed trees§ | 2 (1.4) | | |
| Mixed grasses, | 4 (2.9) | 178 (20.1) | 248 (39.8) |
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The results of this study demonstrate a very low prevalence of allergic sensitization in Amish children living in northern Indiana. We acknowledge that atopy was assessed by 2 different methods in this study and discrepancies between skin prick test reactivity and specific IgE assays have been reported.2x2Weinmayr, G., Genuneit, J., Nagel, G., Bjorksten, B., van Hage, M., Priftanji, A. et al. International variations in associations of allergic markers and diseases in children: ISAAC Phase Two. Allergy. 2010;
65: 766–775
Crossref | PubMed | Scopus (34) | Google ScholarSee all References However, farm studies in an alpine area of Austria have shown similar differences in atopic sensitization (18.8% vs 32.7%) in farm versus nonfarm children when using skin prick testing.4x4Riedler, J., Braun-Fahrlander, C., Eder, W., Schreuer, M., Waser, M., Maisch, S. et al. Exposure to farming in early life and development of asthma and allergy: a cross-sectional survey. Lancet. 2001;
358: 1129–1133
Abstract | Full Text | Full Text PDF | PubMed | Scopus (1026) | Google ScholarSee all References
It has been demonstrated previously that early exposures associated with Swiss farm life are protective against the development of atopic disease4x4Riedler, J., Braun-Fahrlander, C., Eder, W., Schreuer, M., Waser, M., Maisch, S. et al. Exposure to farming in early life and development of asthma and allergy: a cross-sectional survey. Lancet. 2001;
358: 1129–1133
Abstract | Full Text | Full Text PDF | PubMed | Scopus (1026) | Google ScholarSee all References; however, the Amish in our study had a significantly lower prevalence than the Swiss farm children. The parental reporting of wheezing was similar in both the Amish and Swiss farm children. A study of children living in rural areas of Crete demonstrated a lower prevalence of atopy based on skin testing than in children living in a city.6x6Zekveld, C., Bibakis, I., Bibaki-Liakou, V., Pedioti, A., Dimitroulis, I., Harris, J. et al. The effects of farming and birth order on asthma and allergies. Eur Respir J. 2006;
28: 82–88
Crossref | PubMed | Scopus (23) | Google ScholarSee all References The prevalence of allergic sensitization was 24%, again very similar to that in the Swiss farm children. This level of sensitization was found in 4 rural areas with no difference in those living on farms. This study again suggests a protective effect of rural life. Significant differences in allergic sensitization in children were also found in a study of 3 Chinese cities.7x7Wong, G.W., Ko, F.W., Hui, D.S., Fok, T.F., Carr, D., von Mutius, E. et al. Factors associated with difference in prevalence of asthma in children from three cities in China: multicentre epidemiological survey. BMJ. 2004;
329: 486
Crossref | PubMed | Google ScholarSee all References Children living in the Westernized city of Hong Kong had twice the prevalence of atopy as children living in Beijing. There was also a significantly higher prevalence of wheeze in the children living in Hong Kong. In this study, exposure to cotton quilts and raw fruits and vegetables were protective factors.
This Amish population of children aged 6 to 12 years has a very low prevalence of allergic sensitization. Because of the small number of children in the study, we were not able to determine specific differences in lifestyle, diet, exposures, or family history between those Amish children who were sensitized and those who were not sensitized. Among the factors thought to be associated with this low prevalence may be large family size.8x8Strachan, D.P. Hay fever, hygiene, and household size. BMJ. 1989;
299: 1259–1260
Crossref | PubMed | Google ScholarSee all References The Amish families have a mean of 5.9 children per family as compared with 2.4 for the Swiss nonfarm families. All the Amish children and the Swiss farm children had exposure to large animals and a significant percentage consumed milk directly from the farm. Recent studies have implicated a protective effect from farm milk. In one study, certain whey proteins in farm milk were inversely associated with asthma.9x9Loss, G., Apprich, S., Waser, M., Kneifel, W., Genuneit, J., Buchele, G. et al. The protective effect of farm milk consumption on childhood asthma and atopy: the GABRIELA study. J Allergy Clin Immunol. 2011;
128: 766–773 ()
Abstract | Full Text | Full Text PDF | PubMed | Scopus (131) | Google ScholarSee all References The Amish are of Swiss descent and therefore have a genetically similar background to the comparative Swiss children. However, the nonfarm Swiss children have a prevalence of allergic sensitization similar to the National Health and Nutrition Examination Survey data of randomly selected Americans, suggesting no protective genetic effect of Swiss decent. The prevalence of asthma and allergic sensitization continues to rise in the Westernized populations. Although we have not determined specific mechanisms, this study continues to support the effect of early farm exposures and their impact in significantly reducing the prevalence of asthma and allergic sensitization. Previous studies in Switzerland and Crete show a protective effect of farm life or rural living, with a 50% reduction in the prevalence of allergic sensitization as compared with nonfarm or urban living. Therefore, given the exceedingly low level of sensitization of 7.2% among Amish children, we feel that there may be additional protective factors in this population.
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