Prevalence Of Atopic Sensitization Research Articles

Comparative prevalence of atopic sensitization in the border areas between Russia and Finland

Current century has been highlighted with rise in allergic pathology, and environment markedly affects it via epigenetic mechanisms. Allergy research in Russia and Finland has been conducted for many years, of larger scale recorded in the latter, still being maintained over time. Atopy prevalence was studied in the border areas in both countries. The level of total, dietary, inhaled IgE level, as well as dietary and inhalation range were examined. The Phadiatop® radio allergen sorbent test was used (UniCAP 1000 v.2; Pharmacia Upjohn, Uppsala, Sweden), with cut-off point: IgE 110 kUA/l and sIgE 2.5 kUa/l and 0.35 kUA/l. The study was subdivided into 2 stages conducted during 2003 and 2010/2012 timeframe. Stage 1 was performed with children from Finland (n = 344), Russia (n = 427), aged 7—15 years, whereas stage 2 — 180 subjects (Finland, n = 98, Russia, n = 82). Results. It was found that total IgE level was higher in children from Finland. The inhaled sIgE in 2003 and 2010/2012 was higher among children from Finland, p = 0.019 and p = 0.027, showing temporal elevation. In 2003, dietary sIgE was higher among those from Finland (27.6% and 18.3%), p = 0.142, whereas in 2010/2012 it was decreased by 2- and 3-fold in subjects from Finland and Russia, respectively. In 2003, high atopy rate against dust mites, cats, timothy, birch, and dogs was found in Russia, which was increased at stage 2. Such parameter was most evidently elevated for timothy — by 2-fold, p = 0.176, wormwood — by 2-fold, p = 0.312, equine allergens — by 2-fold, p = 0.563, canine allergens — by 1.5-fold, mite — by 1.5-fold, p = 0.220. In 2003, atopy rate in Finland to canine allergens reached 26.5%, timothy — 24.5%, birch — 20.4%, feline allergens — 20.4%. In 2010, it was noted rise in atopy rate mainly to dust mites — by 2-fold, equine allergens — by 2-fold. In 2003, atopy rate in Russia to egg, milk, and wheat prevailed, whereas in Finland it was mostly found against milk, nuts, wheat, eggs, in both cases declined in dynamics. Interestingly, no sensitization to fish in subjects from Russia and Finland was observed at both stages. Finally, at the stage 2 dietary atopy rate was declined in both countries. Differences in atopic sensitization as well as during 7—9 year follow-up observation were preserved between both subject cohorts from Finland and Russia.

Recurrent wheeze and its relationship with lung function and airway inflammation in preschool children: a cross-sectional study in South Korea

BackgroundRelationship between recurrent wheeze and airway function and inflammation in preschool children is not fully known.ObjectiveTo investigate the relationship between recurrent wheeze and airway inflammation, lung function, airway hyper-reactivity (AHR)...

Green Areas Around Homes Reduce Atopic Sensitization in Children

The “biodiversity hypothesis” suggests that exposure to greater environmental biodiversity in the natural flora and fauna can contribute to immune tolerance. The aim of this study was to test this hypothesis by assessing the environments near children’s homes in relation to atopic sensitization.Combined data from 3 studies that were completed in Finland and Estonia from 2003 to 2012, including a total of 1044 children aged 0.5 to 20 years.Three data sets were used that included children from diverse environments in Finland and Estonia. The prevalence of atopic sensitization was determined by measuring serum specific immunoglobulin E to common inhalant allergens. Five land types around the homes of the children were calculated using a standardized classification: forest, agricultural land, built area, water bodies, and wetland areas.The cover of forest and agricultural land within 2 to 5 km from the home was inversely and significantly associated with atopic sensitization. This was seen in patients older than 6 years, and the association was stronger in boys compared with girls and among children exposed to a dog at home. Skin microbiota showed a relative abundance of Proteobacteria that was significantly correlated with the land-use gradient in healthy but not atopic individuals, supporting the hypothesis of a strong environmental effect on the commensal microbiota.Atopy is linked with low accessible green space (forest and agricultural land) within 2 to 5 km from the home. Early life exposure to green environments appeared to be most important. The loss of natural green areas and environmental biodiversity in developed countries leads to a decrease in beneficial environmental microbes and the development of atopy.This fascinating study is 1 of a series that has emerged from Finland relating a variety of dietary and environmental factors to the development of allergic and other inflammatory diseases. Given the rising prevalence of allergic disease, it is extremely important that we understand the role that environmental factors, especially in early life, may play in the development of allergy so that preventive strategies might be developed. Although more studies in different environments are needed, specifically with more in-depth assessment of microbial exposures, data from these studies conducted in Finland clearly support the biodiversity hypothesis.

The association between flexural eczema, rhinitis, asthma and atopic sensitization in Albanian schoolchildren

Background Atopic dermatitis (AD) is a common, relapsing, inflammatory skin disease that primarily affects young children, in which allergic sensitization is present in only a part of patients. Patients with AD may develop allergic rhinitis and asthma at certain ages. In Albania, prior to the ISAAC Phases survey, very little was known about the prevalence of allergic disorders. To give a recent view of the situation was conducted ALB- ISSAC study during the school year 2011-2012 in Tirana, Albania. Methods ALB- ISAAC study was based on ISAAC protocols. Symptoms core and risk factor questionnaires, allergen skin prick tests, examination for visible flexural dermatitis were completed in a schedule according to the study protocol. In August 2011, a randomized sample of schools was chosen until a predefined sample of 3000 children for each of three age groups; 6-7, 10-11 and 13-14 years old were achieved. Results In 6-7 years old the frequency of eczema ever and visible flexural dermatitis were respectively 1.8% and 1.3%, in 1314 years old were 2.5% and 0.6%, and in 10-11 years old were 1.7% and 1.3%. The prevalence of sensitization for any allergen was 24.3 % (258/1093). Wheeze ever (OR= 1.50, 95% CI 1.04- 2.17), asthma ever (OR= 2.72, 95% CI 1.36-5.43) and hay fever ever (OR= 2.24, 95% CI 1.244.07) were more common among the children with positive skin prick test. While, wheeze past 12 months (OR= 1.71, 95% CI 0.98-2.98) and Nose/eyes past 12 months (OR= 1.74, 95% CI 0.96-3.15) were more frequent among 10-11- years -old with positive SPT, but with no statistical significance. Visible flexural dermatitis was three times more frequent among 10-11-year-olds with positive skin prick tests in 2011-2012 (OR =3.16, 95% CI 1.47-6.82). Discussion The prevalence of eczema symptoms, and visible flexural dermatitis at examination, already below the global average in 1995, has remained stable. Alb-ISAAC study found a significant increase in the prevalence of atopic sensitization. Our study found that, the visible flexural dermatitis, wheeze ever, hay fever ever, asthma ever were more frequent among 10-11 years old with positive skin prick test. Different authors tend to identify different phenotypes of atopic dermatitis and even different phenotype of atopy to evaluate the progression toward rhinitis and asthma. It seems that only the allergic extrinsic form follow the distribution and risk pattern that have been assign to asthma and hay fever.

Green areas around homes reduce atopic sensitization in children.

BackgroundWestern lifestyle is associated with high prevalence of allergy, asthma and other chronic inflammatory disorders. To explain this association, we tested the ‘biodiversity hypothesis’, which posits that reduced contact of children with environmental biodiversity, including environmental microbiota in natural habitats, has adverse consequences on the assembly of human commensal microbiota and its contribution to immune tolerance.MethodsWe analysed four study cohorts from Finland and Estonia (n = 1044) comprising children and adolescents aged 0.5–20 years. The prevalence of atopic sensitization was assessed by measuring serum IgE specific to inhalant allergens. We calculated the proportion of five land-use types – forest, agricultural land, built areas, wetlands and water bodies – in the landscape around the homes using the CORINE2006 classification.ResultsThe cover of forest and agricultural land within 2–5 km from the home was inversely and significantly associated with atopic sensitization. This relationship was observed for children 6 years of age and older. Land-use pattern explained 20% of the variation in the relative abundance of Proteobacteria on the skin of healthy individuals, supporting the hypothesis of a strong environmental effect on the commensal microbiota.ConclusionsThe amount of green environment (forest and agricultural land) around homes was inversely associated with the risk of atopic sensitization in children. The results indicate that early-life exposure to green environments is especially important. The environmental effect may be mediated via the effect of environmental microbiota on the commensal microbiota influencing immunotolerance.

Geographical variations in the prevalence of atopic sensitization in six study sites across Canada

Geographical variations in atopic sensitization in Canada have not been described previously. This study used the standardized protocol of the European Community Respiratory Health Survey-1 (ECRHS-1) to investigate the distribution and predictors of atopic sensitization in six sites across Canada and to compare the results with some ECRHS-1 centers. Adults aged 20-44 years in six study sites across Canada underwent allergy skin testing using 14 allergens (Dermatophagoides pteronyssinus, Dermatophagoides farinae) cat, cockroach, grasses (Timothy grass, Kentucky grass), molds (Cladosporium herbarium, Alternaria alternata, Aspergillus fumigatus, Penicillium), trees (tree mix, birch, Olea europea), and common ragweed. The overall prevalence of atopy (skin test over 0 mm to any allergen) was 62.7%. There was significant geographical variation in the prevalence of atopy in the six study sites (lowest 55.6% [95% C.I.51.3-59.9] in Prince Edward Island, highest 66.0 [61.7-70.3] in Montreal) and of sensitization to each of the allergens tested even after adjustment for confounders. When the first eight of the nine allergens in the ECRHS were used to estimate the prevalence of atopic sensitization, the prevalence of atopy in Canada was 57% compared with 35.2% overall for centers in the ECRHS. The prevalence of atopy in Vancouver (57% [52.3-61.8]) was close to that of Portland, Oregon (52.1% [46.2-58.0]). There was a significant variation in atopic sensitization among different study sites across Canada. The prevalence of atopic sensitization is relatively high in Canada compared with sites in the ECRHS and this may, in part, account for the high prevalence of asthma and asthma symptoms in Canada.

The cohort of young Danish farmers – A longitudinal study of the health effects of farming exposure

Working in agriculture poses a serious risk for development of respiratory diseases, especially when working in animal housing. Animal workers are exposed to a mixture of organic and inorganic dust together with fumes and gases, including allergens and microbial-associated molecular patterns with a potentially major impact on respiratory health and the immune system. Exposure to microbial agents in animal housing is associated with an increased prevalence of respiratory symptoms, including bronchial hyperresponsiveness, accelerated lung function decline, and neutrophil-mediated inflammation. These clinical findings are often seen without IgE-mediated sensitization. In fact it has been found in recent studies that the prevalence of atopic sensitization and atopic asthma is low among farmers compared with other populations. The SUS study was designed to identify the type and occurrence of respiratory symptoms and disease, and to investigate risk factors for respiratory disorders and changes in lung function among young farming students. The cohort of young Danish farmers was established in 1992/1994 and followed up in 2007/2008 with a participation rate of 51.7%. The cohort consists of 1734 male farming students, 230 female farming students, and 407 army recruits as controls.

Skin prick test reactivity to common allergens among women in Entebbe, Uganda

SummaryThe objectives of this study were to estimate the prevalence of atopic sensitization, and to identify common aeroallergens associated with atopic sensitization among women in Entebbe, Uganda, and to determine risk factors for atopic sensitization among those with and without a history of asthma or eczema. A case–control study was conducted within a trial of deworming in pregnancy, approximately 2 years after the intervention. Skin prick test reactivity was assessed among 20 women with a history of asthma, 25 with history of eczema and 95 controls. Overall prevalence of reactivity was estimated by adjusting for the prevalence of asthma in the whole cohort. Overall skin prick test prevalence was: any allergen 30.7%, Blomia tropicalis 10.9%, Dermatophagoides mix 16.8%, cockroach 15.8%. The prevalence of a positive skin prick test was significantly associated with a history of asthma (70% to any allergen vs. 32%, P = 0.002) but not with a history of eczema (44% vs. 36%, P = 0.49). Women with Mansonella perstans had significantly reduced odds for atopic sensitization (adjusted odds ratio 0.14, 95% CI 0.03–0.69); women with a history of asthma were less likely to have hookworm (adjusted odds ratio 0.24, 95% CI 0.07–0.81) but this association was weaker for women with a history of eczema. [Clinical Trial No. ISRCTN32849447]

Sentinel health department project in Baden-Wuerttemberg (Germany) – a useful tool for monitoring children's health and environment

In the Federal State of Baden-Wuerttemberg, Germany, an environmental health surveillance system has been established focusing on children aged 10 years. Four study regions (two larger cities, one small city, and one rural area) were designated in order to get information about the body burden of persistent chemicals (toxic metals and chlorinated compounds) in children and about lung function, frequency of respiratory diseases, and allergies. From 1992/1993 to 2002/2003, seven cross-sectional investigations were carried out, and more than 10,000 children took part in the study. DDE, HCB, PCB-138, PCB-153 and PCB-180 were measured in individual blood samples of about 400 children per year, whereas PCDD/PCDF and coplanar PCBs were determined in pooled blood samples. From 1993 to 2003, blood concentrations of these compounds decreased 2 to 4-fold. Concerning regional differences, slightly lower concentrations of DDE, PCBs and PCDD/PCDF could be seen in children from the municipal population of Mannheim compared to other regions. Breast feeding was associated with considerably higher concentrations of PCBs and most other chlorinated compounds. Static and dynamic lung function parameters showed no differences between the investigated areas. For prevalences of respiratory diseases and allergies, no time trend was observed except for pertussis, which showed a decrease in 2002/2003 probably due to an increase of vaccination rates. In addition, the prevalence of atopic sensitization against aero allergenes remained unchanged at about 35% during the observation period. In conclusion, this environmental health survey delivers objective data about spatial and temporal trends and provides information about possible sources of children's exposure to toxic compounds in the environment. Adaptations of the survey to new problems are discussed.

Environmental exposures, genetic predisposition and allergic diseases: one size never fits all

A remarkable increase in the prevalence of allergic diseaseappears to parallel the postindustrial lifestyle changes inwesternized societies. Insufficient microbial exposureduring infancy and early childhood is one of the proposedexplanations for the increase in prevalence of atopicsensitization and associated clinical phenotypes (asthma,allergic rhinitis, eczema). Within this context, childhoodvaccination may be associated with an increased risk ofallergies [e.g. children whose parents refuse the vaccin-ation have less atopic diseases (1)]. However, it has to beemphasized that major benefits of childhood vaccinationprogrammes and successes in the prevention and treat-ment of infectious diseases (with global reduction inmortality and morbidity) clearly outweigh the risk of thepossible promoting effect on allergic disease.There is growing evidence that one of the inadvertentconsequences of the fight against infectious diseases andour obsession with cleanliness might have been theinterference with the immune system development. Thechanging pattern of microbial exposure, with the declinein some infectious diseases, may lead to a slowermaturation of the immune system, with a delayeddevelopment of the optimally balanced immune re-sponses. This notion forms the immunological basis ofthe hygiene hypothesis. However, the hygiene hypothesisoriginated from epidemiological studies.Searching for the cause of allergy: the link between epidemiologyand immunologyFamily size. The pioneering proposal by David Strachanthat a decrease in family size reduced the possibility ofcross-infections, facilitating the clinical expression ofallergic rhinitis had lead to intense interest in this area(2). His findings were confirmed in a number of studies(3), and within the same context, exposure to otherchildren in day-care centres was found to be protectiveagainst asthma and atopy (4). Yet, the effects of familysize, position in sibship or day-care arrangements maynot be mediated by the exposure to infectious agents,but some other underlying aspect of immune response(5).Helminths. Children in developing countries who areinfested with helminths are less likely to develop atopyand allergic disease. Furthermore, long-term treatment ofintestinal helminths in infested children increases specificsensitization to house dust mite (6). In addition, thereappears to be an inverse dose-response relationshipbetween the burden of infestation by helminths andexpression of allergic disease (7). However, helminthsmay only be a marker of environmental exposure to othermicrobial agents and/or endotoxin.Helminthic infections enhance the secretion of T

Skin Test Reactivity Among Danish Children Measured 15 Years Apart

Background: Knowledge of secular trends in the prevalence of allergy among children stems in large part from questionnaire surveys, whereas repeated cross-sectional studies using objective markers of atopic sensitization are sparse.Objectives: To investigate whether the prevalence of skin prick test (SPT) positivity in Danish children has changed from 1986 to 2001.Methods: Serial cross-sectional studies of two different random population samples of children aged 7 to 17 years of age, living in urban Copenhagen, Denmark, were performed 15 years apart. The first cohort was investigated in 1986 (n = 527) and the second in 2001 (n = 480). Skin test reactivity to nine common aeroallergens was measured at both occasions.Results: The prevalence of positive SPT to at least one allergen decreased from 24.1% in 1986 to 18.9% in 2001, (p = 0.05). We found a declining prevalence of sensitization to most allergens tested, statistically significant; however, only for mugwort and Alternaria iridis. Among subjects, who were sensitized to only one allergen, we found significantly fewer individuals with reactions to D. pteronyssinus and mugwort.Conclusions: The prevalence of atopic sensitization as judged by SPT positivity has decreased or remained unchanged among Danish children during the 15-year period from 1986 to 2001. The increase in prevalence of allergic disease often reported in comparable studies using questionnaires as sole diagnostic criterion could not be reproduced in this study where objective markers of allergic sensitization were included in the design.

Surveillance for atopic sensitization in infants and young children by skin prick test

Rationale Skin prick test (SPT) is considered to be the simple and sensitive method for detecting atopic sensitization in children. Factors that influence atopic sensitization in people from different ethnicity may vary. We performed SPT to study the prevalence of atopic sensitization, and the effect of atopic family history and environmental factors on prevalence of atopic sensitization and atopic manifestation in Thai children. Methods After obtaining the informations on atopic history and atopic manifestation, SPT with 10 common standardized allergens was performed in infants and children from well baby clinic, age range from 6 months to 3 years. Results Two hundred subjects were studied. Atopic family history was presented in 54.9% and atopic manifestation in 31.9% of subjects. Overall prevalence of atopic sensitization was 37.2%. Dermatophagoides pteronyssinus (Der p) and Dermatophagoides farinae (Der f) were found to be the most prevalent allergens eliciting positive SPT (15%). The most prevalent allergen sensitization in subjects age 6-12 months, 1-2 years and 2-3 years were egg (15%), Der p (10.5%) and Der f (37.1%) respectively. Interestingly there was no significant effect of atopic family history on atopic sensitization or atopic manifestation. Day care attendance was significantly associated with increase risk of sensitization to Der f ( P<0.005). Conclusions From our study atopic sensitization was associated with day care attendance but not atopic family history. Different factors may influence atopic sensitization in different parts of the world.

Lipopolysaccharide-induced suppression of airway Th2 responses does not require IL-12 production by dendritic cells.

The prevalence of atopic asthma, a Th2-dependent disease, is reaching epidemic proportions partly due to improved hygiene in industrialized countries. There is an inverse correlation between the level of environmental endotoxin exposure and the prevalence of atopic sensitization. As dendritic cells (DC) have been implicated in causing sensitization to inhaled Ag, we studied the effect of endotoxin on Th2 development induced by bone marrow DC in vitro and by intratracheal injection in vivo, with particular emphasis on the role played by the polarizing cytokine IL-12. Bone marrow-derived DC stimulated with Escherichia coli O26:B6 LPS produced IL-12p70 for a limited period of time, after which production became refractory to further stimulation with CD40 ligand, a phenomenon previously called "exhaustion." The level of IL-12 production of DC did not correlate with Th1 development, as exhausted OVA-pulsed DC were still capable of shifting the cytokine pattern of responding OVA-specific Th cells toward Th1 in vitro and in vivo. When mice were first immunized by intratracheal injection of OVA-DC and subsequently challenged with OVA aerosol, prior in vitro stimulation of DC with LPS reduced the development of airway eosinophilia and Th2 cytokine production. Most surprisingly, the capacity of LPS to reduce Th2-dependent eosinophilic airway inflammation was IL-12-independent altogether, as IL-12p40 knockout DC had a similar reduced capacity to prime for Th2 responses. These results suggest that LPS reduces sensitization to inhaled Ag by reducing DC-driven Th2 development, but that IL-12 is not necessary for this effect.

Are infections protecting from atopy?

The 'Hygiene Hypothesis' proposes that overcrowding and unhygienic contacts early in life may protect from atopic diseases by facilitating exposure to microbes. Longitudinal studies have recently shown that among subjects exposed early in life to other children at home, or at day care, the risk of wheezing steadily declined with age to levels significantly lower than controls. Evidences supporting a protective role of respiratory infections or BCG immunization on the development of allergic asthma are still insufficient. By contrast, the observation of a lower prevalence of atopic sensitization among children raised on a farm has been consistently reproduced. Several new studies have recently investigated the role of changes of human microbial flora, declining exposure to foodborne and orofecal infections, to helminths and to environmental sources of endotoxin as putative contributors to the rise of allergy and asthma cases among populations living with a western lifestyle.

Allergische Rhinitis und Sensibilisierungsraten - Nimmt die Prävalenz wirklich zu?

Numerous epidemiological studies indicate an increase in the prevalence of allergic diseases. However, the estimations of the prevalence are very often based on questionnaire data only. Additional objective measurements e.g. of allergen-specific IgE antibodies were included only in a few surveys. Since the public awareness of allergic diseases has increased, too, the question arose, whether the reported increase represents a true rise in the frequency of allergies or simply reflects greater recognition of allergic diseases. Little is known about the time trend in the prevalence of allergic rhinitis and sensitisations in adults in Germany. To prove, how reliable the prevalence data are, different sources of information (questionnaire, interview, specific IgE measurements) were compared. Additionally, to investigate whether the risk of atopic sensitisation and the risk of allergic rhinitis has increased in Germany, too, data of cross-sectional studies, conducted 6 – 8 years apart were compared. There is strong evidence that the prevalence of both, allergic rhinitis and sensitisations increased in the last years. In total, the rate of sensitisations increased from 27% to 31% and the prevalence of atopic rhinitis from 8% to 13%. In adults, under the age of 45, the prevalence is much higher than in adults aged 45 to 79 years. The prevalence of atopic sensitisation is 38% in the age group of 20 – 44 years and 23% in the older group, and the prevalence of allergic rhinitis (positive allergen-specific IgE test and reported allergic rhinitis) is 15% in the younger and 5% in the older group (prevalence in the last 12 months).

Similar prevalence of respiratory symptoms and atopy in Estonian schoolchildren with changing lifestyle over 4 yrs.

The prevalence of allergic sensitization and clinical manifestations is low in Eastern Europe, despite a continuous increase in industrialized countries with a market economy. The aim of the present study was to study changes in the prevalence of respiratory symptoms and atopic sensitization over time among schoolchildren in Estonia, in relation to environmental changes as the country transformed into a market economy. A cross-sectional study of 10-yr-old children was carried out between October 1996 and April 1997, employing a questionnaire regarding the prevalence of wheezing, rhinitis and itching rash (n=979) and skin-prick tests with seven inhalant allergens (n=640). The results were compared with those of a similar study performed in 1992-1993. The 12-month prevalence of wheeze was 8.3%, as compared to 9.4% in 1992-1993 (NS) and of asthma was 2.5 versus 3.2% (NS). The prevalence of a positive skin-prick test result was 14.3% in both studies. Furthermore, the prevalence of sensitivity to the individual allergens was similar, except for a significantly higher prevalence of dog sensitivity in 1996-1997 (4.7 versus 2.0%). The prevalence of respiratory and other potentially allergic symptoms, as well as the prevalence of atopic sensitization, remains low in Estonian 10-yr-old children, despite a changing lifestyle over the past 4 yrs. This could indicate that the time period was too short for environmental changes to affect the prevalence of allergy, or alternatively that risk factors associated with a "western lifestyle" are of particular significance earlier in life.

Allergy against chironomids (non biting midges) in adult atopic patients

The aim of this investigation was to evaluate the prevalence of atopic sensitization to chironomids (CHI) in patients with asthma and/or rhinitis (A/R), and to study concomitant sensitization to CHI and other allergens. Skin prick tests were performed with 3 different CHI extracts as well as with common inhalant allergens in 600 consecutive patients, 495 of which had A/R. Allergen specific IgE antibodies in the sera against CHI, shell fish and cockroaches were analyzed with Magic Lite.

Urban living as a risk factor for atopic sensitization in Swedish schoolchildren

The prevalence of atopic sensitization was compared among all pupils in three urban school classes (median age 10, 12 and 14 years, respectively) and three corresponding classes in the adjacent rural district (642 pupils in all). A written questionnaire, oral interview and skin prick testing against 7 allergens were used, with skin tests performed on 93.4 % of the urban, and 92.0 % of the rural pupils. Contact with domestic animals was much more common in the rural area. Urban living was a risk factor for at least one positive skin test to pollen or animal dander, with odds ratio (OR) 1.83 and confidence interval (CI) 1.26–2.67. This was even more pronounced for children with both positive skin test and allergic symptoms (OR 2.13; CI 1.38–3.28). An increased prevalence of positive skin prick tests in the urban area compared with the rural environment was also found for 3 individual allergens, i.e. birch pollen (OR 1.78), timothy pollen (OR 1.87) and cat dander (OR 2.29). The relative risk for positive skin test in the urban area was further increased when standardized for allergic heredity, type of dwelling, daily exposure to tobacco smoke and dampness or abnormal smell in the home. This study suggests that various adjuvant factors increase the risk of sensitization in urban environments, particularly among children with a positive family history of allergy