TABLE VI.G.3.
Evidence for the hygiene hypothesis in the development of allergic rhinitis
Study | Year | LOE | Study design | Study groups | Clinical endpoint | Conclusion |
---|---|---|---|---|---|---|
Campbell et al.647 | 2015 | 2a | SR | 29 studies (1999–2014): 26 cross-sectional, 3 longitudinal. Meta-analysis: 8 studies | Association of farm exposure with sensitization in childhood or adulthood | Protective effect of farm exposure in infancy on allergic disease in childhood and adulthood in majority of studies. Exposure during adulthood had no consistent relationship with sensitization. |
Karmaus & Botezan645 | 2002 | 2a | Meta-analysis | 53 studies (1986–2000). Hay fever: 17 studies (n = 253,304); Sensitization: 16 studies (n = 46,758) | Association of sensitization and AR with 3 or more siblings vs no siblings | Higher number of siblings was associated with less atopy. Effect was not explained by hygiene factors. |
Fujimura et al.645 | 2016 | 2b | Longitudinal birth cohort study | 298 children followed until age 4 years | Association of sensitization and asthma at age 2 years with fecal microbiota in neonates targeted at age 1 month (n = 130) or 6 months (n = 168) | Reduced colonization of Bifidobacteria, Lactobacillus, Faecalibacterium, Akkermansia, and Malassezia during the neonatal period may influence the risk of multisensitization predictive for asthma. |
House et al.648 | 2016 | 2b | Nested case-control study | Farmers and spouses: Cases: asthma (n = 1198); Controls: no asthma (n = 2031). | Association of sensitization, rhinitis, eczema, and asthma with living on a farm when born and with being exposed to farm environment when mother was performing farm activities during pregnancy | Early-life farm exposure associated with less atopy. No association with asthma. |
Hua et al.664 | 2016 | 2b | Cross-sectional study | 1879 adult subjects | Association of seasonal allergy with fecal microbial biodiversity | Reduced fecal biodiversity and altered composition associated with more allergy. No association with asthma and eczema. |
Arrieta et al.663 | 2015 | 2b | Longitudinal nested case-control study | 319 children followed from birth until 5 years of age | Association of sensitization and wheezing at 1 year with fecal microbiota at age 3 months and 1 year | Reduced colonization of Faecalibacterium, Lachnospira, Veillonella, and Rothia during the first 3 months of life may increase the risk of atopic asthma. |
Strachan et al.646 | 2015 | 2b | Cross-sectional study | Children 6–7 years of age in 31 countries (n = 210,200); 13–14 years of age in 52 countries (n = 337,226) | Association of hay fever with three or more siblings vs no siblings | Protective effect of older and total number of siblings on self-reported AR. Effect was significantly stronger in affluent countries. |
Valkonen et al.661 | 2015 | 2b | Cross-sectional stratified population study | GABRIELA study: 224 children, 6–12 years | Association of sensitization with mattress bacterial diversity | Exposure to more diverse bacterial flora associated with less sensitization. |
Bisgaard et al.449 | 2011 | 2b | Longitudinal study | 253 high-asthma-risk children followed from birth to age 7 years | Association of sensitization and AR with high fecal microbial biodiversity | Reduced bacterial diversity associated with higher risk of sensitization and AR in childhood. |
Ege et al.659 | 2011 | 2b | Two cross-sectional studies | PARSIFAL study: 489 rural and suburban children; GABRIELA study: 444 rural children | Association of sensitization with microbes in mattress (PARSIFAL) and in airborne dust (GABRIELA) | Farm-children had less asthma and atopy. Indoor microbial exposure much higher and diverse in farm homes. Microbial diversity related to asthma but not to atopy. |
Tischer et al.657 | 2011 | 2b | Nested case-control study | 678 children at the age of 6 years from German (n = 346) and Dutch (n = 332) birth cohorts | Association of rhinitis and asthma with mattress dust biological components of mold and endotoxin | Inconsistent results. Microbial exposures at home had different effects on allergy in German and Dutch birth cohorts. |
von Hertzen et al.660 | 2007 | 2b | Cross-sectional study | 563 children aged 7–16 years in Finnish and Russian Karelia | Association of sensitization with microbial content in drinking water samples from school kitchens | Microbial count much higher and sensitization much lower in Russia. High count of microbes associated with less atopy. |
Cuello-Garcia et al.658 | 2015 | 3a | Systematic review and meta-analysis | 29 randomized controlled trials in infants | Association of AR with probiotic supplementation to pregnant mothers, breast-feeding women, or infants | No effect on allergies. |
Simpson & Martinez656 | 2010 | 3a | Review | (2000–2007): 6 rural studies; 10 urban studies | Association of sensitization with exposure to endotoxin | Exposure to endotoxin protective in over 50% of studies. Endotoxin may be marker of other protective factors. |
Abrahamsson et al.442 | 2014 | 3b | Longitudinal case-control study | 47 infants (n = 20 IgE-associated eczema; n = 27 healthy controls) followed until 7 years of age | Association of sensitization, asthma and AR with fecal diversity in infancy | Low microbial diversity associated with asthma later in childhood. No association with sensitization or rhinitis. |
AR = allergic rhinitis; GABRIELA = GABRIEL Advanced Survey; IgE = immunoglobulin E; LOE = level of evidence; PARSIFAL = Prevention of Allergy-Risk Factors for Sensitization Related to Farming and Anthroposophic Lifestyle; SR = systematic review.