Indoor allergen exposure is a risk factor for sensitization during the first three years of life

Are maternal psychosocial factors associated with cord immunoglobulin E in addition to family atopic history and mother immunoglobulin E?

BACKGROUND

Atopy in maternal and family histories is known to be a risk factor for elevated umbilical cord immunoglobulin E (cIgE). However, the association between cIgE and psychosocial factors remains under investigation.

OBJECTIVE

To explore whether psychosocial factors in addition to atopy contribute to elevated cIgE.

METHODS

Four private maternity hospitals fitting the quantile levels of SO(2) in 2000 cooperated with us by recruiting participants for this study: pairs of mothers and neonates living within 3-km catchment areas of air-monitoring stations. We used a questionnaire to collect exposure data, and the Pharmacia UniCap IgE assay test system to determine the levels of IgE in gravidas and cord blood.

RESULTS

Between July 2001 and March 2003, 334 mother and neonate pairs participated in this study. The frequencies of sensitization, serum IgE (sIgE)>100 IU/mL, or cIgE> or =0.35 IU/mL were not different between the four different hospitals. By multi-variate logistic regression analysis adjusted for environmental factors, genetic factors, and psychosocial factors, the risk factors for elevated cIgE were being a male neonate (odds ratio (OR)=3.5, 95% confidence interval (CI)=[1.5, 8.5]), carpets at home (OR=3.0, 95% CI=[1.02, 8.4]), maternal allergy to dog dander (OR=9.7, 95% CI=[1.2, 98.8], maternal total serum IgE>100 IU/mL (OR=5.1, 95% CI=[2.2, 12.8]), maternal regularly/mostly/often self-reported nervousness (OR=4.0, 95% CI=[1.3, 12.8]), family income 11,574-17 361 US dollars/year (OR=3.7, 95% CI=[1.3, 11.5]), incense burning (OR=4.0, 95% CI=[1.4, 13.3]), and atopy in maternal grandparents (OR=4.8, 95% CI=[1.7, 14.0]). By principle component analysis and logistic regression, psychosocial stress (beta +/- standard error=0.26+/-0.13, P=0.04) was associated with increased cIgE.

CONCLUSION

Psychosocial factors are potentially important risk factors for elevated cIgE.

The influence of air conditioning, humidity, temperature and other household characteristics on mite allergen concentrations in the northeastern United States

BACKGROUND

Information about the influence of housing and occupant characteristics on mite allergen concentrations is crucial to determine which methods could be used to decrease exposure of susceptible subjects.

OBJECTIVES

To identify housing and occupant characteristics that are associated with mite allergen concentrations in house dust collected from living rooms and mattresses.

METHODS

We collected dust samples from 750 homes in the northeastern US. The influence of various characteristics on concentrations of mite allergens (Der p 1 and Der f 1) was studied using multiple linear regression analysis.

RESULTS

Some characteristics, like absence of air conditioners, the presence of mold or mildew, and a lower temperature were consistently associated with higher concentrations of both mite allergens in dust from all sampling locations. However, none of these factors changed Der p 1 or Der f 1 concentrations by more than a factor of 2. People of white ethnic background had roughly two times higher mite allergen concentrations, while family income, family size, and education level only marginally influenced mite allergen concentrations.

CONCLUSIONS

Various housing characteristics have some influence on mite allergen concentrations, and could possibly be used to decrease exposure of susceptible subjects. However, only a limited percentage of the variation in mite allergen concentrations was explained by these characteristics.

Prediction of residential pet and cockroach allergen levels using questionnaire information

We assessed the accuracy of questionnaire reports of cat and dog ownership and presence of cockroaches in predicting measured allergen concentrations in house dust. We collected dust samples in the homes of 932 newborns living in New England. Dust samples were taken from the main living area and the infant's bedding. Allergen content of house dust was measured by enzyme-linked immunosorbent assays (ELISA) and related to questionnaire information on past and current cat and dog ownership and presence of cockroaches. Allergen levels were dichotomized using the limit of detection and the following cut points: 1.0 microg/g and 8.0 microg/g for cat, 2.0 microg/g and 10.0 microg/g for dog, and 2 U/g and 8 U/g for cockroach allergen. For the upper cut point, both specificity and sensitivity of questionnaire-reported cat and dog ownership and presence of cockroaches were high. For the limit of detection and lower cut point, specificity was high (> 80%), whereas sensitivity was low, particularly for current cat and dog ownership (21-60%). Taking pet ownership during the preceding 2 years into account increased the sensitivity by 10%, but it remained relatively poor. In conclusion, questionnaire-reported pet ownership and presence of cockroaches predicts allergen levels above the upper cut point but is a relatively poor measure of allergen exposure above the limit of detection and the lower cut point. Knowledge of past pet ownership can improve pet allergen exposure assessment by means of questionnaire. However, for epidemiologic purposes, measured concentrations of allergens are necessary.

Presence and timing of cat ownership by age 18 and the effect on atopy and asthma at age 28

BACKGROUND

Asthma and allergic sensitization to cats frequently coexist, although recent studies show less atopic disease among people who had pets in infancy. However, no longterm evaluations have been performed thus far.

OBJECTIVE

We sought to evaluate the relationship between cat ownership at different age periods (< 18, > 18, and both periods and atopic disease at age 28.

METHODS

Australian school children aged 8 to 10 years were recruited in 1982 and participated in follow-up surveys until 2002. Cat ownership was defined by surveys in 1992 and 2002 as having a cat before age 18 only, after age 18 only, or in both periods of life. Health outcomes were defined at a mean age of 28.5 years.

RESULTS

Complete data were available for 224 subjects, 50 of whom had a cat before 18 years of age only, 14 after age 18 only, and 70 in both periods. Compared with 90 subjects that never had a cat, having a cat before age 18 protected against atopy to outdoor allergens, airway hyperresponsiveness (AHR) to histamine, current wheeze, and current asthma (P < .05). In contrast, subjects who acquired their first cat after age 18 showed a trend toward higher prevalence rates for asthma symptoms and AHR (P > .10).

CONCLUSIONS

Having had a cat before 18 years of age protects against adult asthma and atopy.

Associations between specific serum IgE response and 6 variants within the genes IL4, IL13, and IL4RA in German children: the German Multicenter Atopy Study

BACKGROUND

Among many published studies of specific IgE response or atopy, only a few showed positive marginal effects for 6 potentially functional single nucleotide polymorphisms (SNPs; C-590T in the IL4 gene, C-1055T and Arg130Gln in the IL13 gene, and Ile50Val, Ser478Pro, and Gln551Arg in the IL4RA gene). SNPs were commonly considered individually, and therefore the true effect could be masked by other genes or environmental factors.

OBJECTIVE

We tested the relationship between these 6 SNPs and sensitization to food, mite, cat, and outdoor allergens in unrelated German children drawn from the Multicenter Atopy Study. Gene-gene and gene-environment interactions were also evaluated.

METHODS

Multiple logistic regression models were used for the analyses of 4 sensitization outcomes.

RESULTS

The variant C-1055T was significantly associated with increased risk of sensitization to food and outdoor allergens, with odds ratios of 3.49 (95% CI, 1.52-8.02) and 2.27 (95% CI, 1.04-4.94), respectively. The effects of the TT genotype on food sensitization appear to depend on variants in the IL4RA gene, in which marginally significant interaction terms were observed. Significant evidence supported an interaction between exposure to maternal smoking and variant Gln551Arg on risk of cat sensitization. In addition, we found that the effect of variant C-590T on sensitization to mite depended on Der p 1 allergen levels in carpet dust samples.

CONCLUSIONS

These findings not only suggested that variants in the IL4, IL13, and IL4RA genes play an important role in controlling specific IgE response but also strengthened our understanding of gene-gene and gene-environment interaction on the development of specific sensitization in this study population.

A prospective study of Fel d1 and Der p1 exposure in infancy and childhood wheezing

The impact of domestic exposure to cat allergen (Fel d1) and house dust mite (Der p1) on wheezing from birth to the age of 4 years was investigated in a multicenter prospective birth cohort; 1,611 mothers were recruited before delivery in Ashford, England, and Barcelona and Menorca, Spain. Exposures were gathered via dust sample collection at children's home in their first year of life. Families provided complete outcome data (wheezing status in all 4 years) for 1,289 children. Domestic allergen levels varied substantially between centers. Six hundred three (47%) children never wheezed during their first 4 years of life. Der p1 did not correlate with any type of wheezing outcome. Fel d1 significantly increased the risk of wheezing in 3- and 4-year-olds in comparison to 1-year-olds. Distinct risk profiles were found for wheezing at different ages. Multivariate analysis revealed an interaction between Fel d1 and maternal asthma among children who wheeze in Year 4 (relative risk = 2.77; 95% confidence interval = 1.19-6.46). Our data support the idea that several patterns of wheezing with different risk profiles exist among young children. The effect of Fel d1 exposure varied according to age and maternal asthma.

Dietary prevention of allergic diseases in infants and small children. Part I: immunologic background and criteria for hypoallergenicity

The role of primary prevention of allergic diseases has been a matter of debate for the last 40 years. In order to shed some light into this issue, a group of experts of the Section of Pediatrics EAACI critically reviewed the existing literature on the subject. In this paper, the immunology of the fetus and newborn is reviewed as well as the post-natal development of the immune system. The influence of post-natal environment and breastfeeding on tolerance induction and sensitization are examined. Allergic diseases result from a strong relationship between genetic and environmental factors. Sensitization to food allergens occurs in the first year of life and cow's milk allergy is the first food allergy to appear in the susceptible infants. Hypoallergenicity of food formulas to be used is a critical issue both for treatment of cow's milk-allergic children and for prevention. Methods to document hypoallergenicity are discussed and evaluated in the preclinical and clinical steps.

Effects of intestinal microflora and the environment on the development of asthma and allergy

The aim of previous research into the causes of allergic diseases, including asthma was mostly to identify potential risk factors in the environment. No major risk factors have been identified, however. Over the past 10 years, focus has, therefore, more been directed towards protective factors that could enhance the development of tolerance to allergens which were previously encountered early in life, but are now lost in modern affluent societies. In particular, the role of childhood infections has been discussed, but so far these studies have not been conclusive. Recent epidemiological studies and experimental research suggest that the microbial environment and exposure to microbial products in infancy modifies immune responses and enhances the development of tolerance to ubiquitous allergens. The intestinal microflora may play a particular role in this respect, as it is the major external driving force in the maturation of the immune system after birth, and animal experiments have shown it to be a prerequisite for normal development of oral tolerance. Recent studies have shown differences in the composition of the microflora between healthy and allergic infants in countries with a high and low prevalence of allergies and between healthy and allergic infants within such countries. These differences are apparent within the first week of life and thus precede clinical symptoms. The use of live microorganisms that might be beneficial to health has a long tradition and the safety is well documented. Very recently, several prospective intervention studies, modifying the gut flora from birth have yielded encouraging results and may suggest a new mode of primary prevention of allergy in the future.

The determinants of dust mite allergen and its relationship to the prevalence of symptoms of asthma in the Asia-Pacific region

The role that house dust mites play in the primary causation of asthma is controversial. Approximately thirty-six 10-yr-old children in each of 10 centres in the Asia-Pacific region participated. Researchers collected dust from mattresses and living room floors using standardized procedures. Der p1 and Der f1 were analysed using a double monoclonal antibody enzyme-linked immunosorbent assay. Geometric mean allergen levels were calculated for each centre. An ecological analysis was conducted to show the regression of the geometric mean allergen level, using the highest household level, against asthma symptom and severity prevalence data from the International Study of Asthma and Allergies in Childhood, Phase I. Among children aged 13-14 yr, the change in asthma symptom prevalence was associated with per unit change in Der p1 microg/g (1.08, 95% CI 0.10-2.06) and Der 1 microg/g (Der p1 + Der f1) (0.64, 95% CI 0.02-1.26). The change in having four or more attacks of asthma in the last 12 months was associated with per unit change in Der p 1 microg/g (0.29, 95% CI -0.02 to 0.60) and Der 1 microg/g (0.20, 95% CI 0.01-0.38). There was no effect for total Der p1 or Der f1 (total or microg/g). Among children aged 6-7 yr, neither allergen was related to symptoms or severity prevalence. While our findings suggest that Dermatophagoides pteronyssinus may have a role in the primary causation of asthma, the complexity of this association reinforces the need for prospective studies.

Effect of indoor environmental factors on development of atopic symptoms in children followed up to 4 years of age

The increased prevalence of atopic diseases reported in many Western countries is thought to be caused by changes in living conditions. For a long time attention was focused on indoor environmental factors and early feeding patterns, but during recent years other factors have received more attention. An unselected, Swedish, population-based cohort of 904 children were followed from the age of 3 months to 4 years. Questionnaires were sent to the mothers of the children when they were 3 months, 18 months and 4 years of age. A blood sample was taken from a subgroup of the children when they were 4 years old which was analysed for IgE specific antibodies to food and inhalant allergens. The prevalences of asthma, allergic eye-nose reactions, eczema, and food reactions at 4 years of age and a positive blood test were analysed as outcome factors. Features of housing and early feeding patterns were found to have limited effect on the development of allergies in the children. Presence of older siblings resulted in a decreased tendency to produce IgE antibodies. Early exposure to furry animals seemed to prevent the development of asthma. Children who were frequently infected up to 18 months of age showed an increased prevalence of allergic symptoms at 4 years of age. Children of mothers with a higher prevalence of complaints about indoor factors, or who had increased general symptoms or skin or mucous membrane symptoms ran a greater risk of developing various allergic symptoms. However, these children did not have higher levels of IgE antibodies. The reported allergic symptoms in the children may be due to non-immunological reactions, although it is also possible that the mothers may have over-reported such symptoms.

Variability of airborne cat allergen, Fel d1, in a public place

Allergen exposure is a risk to develop an IgE-mediated sensitization. The amount of allergen inhaled per unit time should be related to the amount present in the air, i.e. airborne allergen. Thus, measuring allergen levels in the air would be more relevant than measuring allergen levels in dust. Allergens are present in the air in very minute quantities and usually become airborne after disturbance. Large variation of allergen levels have been found in dust. In this study, we measured variability of airborne cat allergen, Fel d1, in a public place using a high-volume air-sampler. We also studied the distribution and relationship between dust and airborne cat allergens in homes and schools. Air samples were collected at three different airflow rates, i.e. 55, 40, and 30 m3 of air per hour. The concentration of airborne Fel d1 in the community gymnastic hall varied from 1 to 10 pg/m3 within a period of 3 weeks, at airflow rates 55-30 m3/h. The coefficient of variation for repeated samplings was 14-43% (day-to-day variation) and 27-38% (within-day variation). As expected, higher levels of airborne cat allergens were found in homes with cats than in cat-free environments. There was a significant relationship between cat allergen levels in dust and air (r=0.7, P<0.01). Our study demonstrates that when measuring airborne cat allergen a large variation is observed within a day and between days. The large variability of measurement may be explained by the disturbance in the environments. We suggest, that when exposure assessment is made the environment in question should be analyzed, if possible in several occasions.

Direct and indirect exposure to pets - risk of sensitization and asthma at 4 years in a birth cohort

INTRODUCTION

There are conflicting data on the association between early exposure to pets and allergic diseases. Bias related to retrospective information on pet ownership has been addressed as a reason for distorted study results.

OBJECTIVE

To elucidate how early exposure to cat and dog relates to IgE-sensitization and asthma in children at 2 and 4 years of age, in a prospective birth-cohort study.

METHODS

Four thousand and eighty-nine families with children born 1994-1996 in predefined areas of Stockholm answered questionnaires on environmental factors and symptoms of allergic disease at birth, one, two and four years of age. Dust samples collected from the mothers' beds at birth were analysed for Fel d 1 and Can f 1 in a subgroup of the cohort. Blood samples taken at four years from 2614 children were analysed for allergen-specific IgE to common airborne allergens. Risk associations were calculated with a multiple logistic regression model, with adjustment for potential confounders.

RESULTS

A correlation was seen between allergen levels and reported exposure to cat and dog. Exposure to cat seemed to increase the risk of cat sensitization, OR (odds ratio) 1.44 (95% confidence interval 1.03-2.01), whereas dog exposure did not have any effect on dog sensitization, OR 1.16 (0.79-1.72). Dog ownership was related to a reduced risk of sensitization to other airborne allergens, OR 0.36 (0.15-0.83), and a similar tendency was seen for cat ownership OR 0.63 (0.37-1.07). Early dog ownership seemed to be associated with a lower risk of asthma, OR 0.50 (0.24-1.03), with no corresponding effect after cat ownership, OR 0.88 (0.56-1.38).

CONCLUSION

Early exposure to cat seems to increase the risk of sensitization to cat but not of asthma at 4 years of age. Dog ownership, on the other hand, appears to be associated with lowered risk of sensitization to airborne allergens and asthma. Both aetiological relationships and selection effects have to be considered in the interpretation of these findings.

Exposure to high doses of birch pollen during pregnancy, and risk of sensitization and atopic disease in the child

BACKGROUND

The role of maternal allergen exposure during pregnancy in sensitization and development of atopic disease in the child remains controversial. In the spring of 1993, extremely high levels of birch pollen were recorded in Stockholm, Sweden. In 1994, the corresponding pollen levels were low. The aim of this study was to assess the influence of exposure during pregnancy to high/low doses of birch pollen on the risk of sensitization and development of atopic disease in children. In addition, a comparison was made with children exposed to birch pollen in early infancy.

METHODS

Three hundred and eighty-seven children with atopic heredity, born in Stockholm in July-October 1993 or 1994 (mothers exposed during pregnancy), were investigated at age 4.5 years. The children were clinically examined and were skin prick tested (SPT) with inhalant and food allergens. IgE antibodies (RAST) against birch pollen and recombinant birch pollen allergen (rBet v 1) were analysed in serum. A comparison was made with a similar group of children exposed during the same incident, but in the first 3 months of life, in 1993.

RESULTS

The children of mothers high-dose exposed during pregnancy in 1993 tended to be more sensitized (SPT > or = 3 mm) to birch pollen than the children with low-dose exposure during the corresponding period in 1994 (7.6 and 4.6%, respectively, OR: 1.7; 95% CI: 0.7-4.1). A similar but weak tendency was seen for positive RAST analyses (> or =0.35 kU/l) against birch pollen and rBet v 1. Children of mothers high-dose exposed during pregnancy were significantly less sensitized to birch pollen than the children high-dose exposed in early infancy (17.9%, OR: 0.4; 95% CI: 0.2-0.7). There was an overall trend towards a slightly increased prevalence of bronchial asthma, allergic rhinoconjunctivitis and atopic dermatitis in the group with mothers high-dose exposed during pregnancy, compared to those with low exposure.

CONCLUSION

Exposure of the mother during pregnancy to high levels of birch pollen resulted in a tendency towards increased risk of sensitization to the same allergen and symptoms of atopic disease in children with atopic heredity. Furthermore, our data indicate that exposure of the mother during pregnancy to inhalant allergens is less likely to result in sensitization in the child than exposure of the child in early infancy.

Associations between total serum IgE levels and the 6 potentially functional variants within the genes IL4, IL13, and IL4RA in German children: the German Multicenter Atopy Study

BACKGROUND

Increased total serum IgE levels are a common characteristic of atopic disorders. Six potentially functional variants, including C-590T in the IL4 gene, C-1055T and Arg130Gln in the IL13 gene, and Ile50Val, Ser478Pro, and Gln551Arg in the IL4RA gene, have been evaluated for their involvement in the control of total serum IgE levels and related atopic disorders, but the results of these studies have been inconsistent.

OBJECTIVE

We examined whether these 6 variants had genotypic effects on total serum IgE levels in 823 unrelated German children from a large infant cohort, the German Multicenter Atopy Study.

METHODS

Marginal effect models were used for the analyses of the repeated IgE measurements. Weighted linear regression and family-based tests of association were performed to minimize the possibility of spurious effects caused by selection bias or confounding on the basis of ethnic background.

RESULTS

There are significant associations between increased total serum IgE levels and 2 variants in the IL13 gene (P <.005 and.0002 for Arg130Gln and C-1055T, respectively). These genetic effects are unlikely to be due to solely linkage disequilibrium between 2 polymorphisms, population stratification, or nonrepresentative samples. In addition, exposure to maternal smoking appears to modify the above effects on total serum IgE levels. However, no statistical association was observed between this quantitative phenotype and the other 4 variants examined.

CONCLUSION

These findings suggest that variants C-1055T and Arg130Gln of the IL13 gene might play an important role on total serum IgE production in this study population.

Four methods of sampling for dust mite allergen: differences in 'dust'

BACKGROUND

Measurement of exposure to the dust mite allergen Der p 1 is important in asthma research and is potentially useful in managing asthma. As no single measure can capture all characteristics of an exposure, it is important to recognize differences in the available methods of measuring exposure to Der p 1.

METHODS

Fourteen bedrooms and living rooms were sampled using four methods for 1 week. Airborne allergen was sampled by static Institute of Occupational Medicine samplers. Settling dust was collected on Petri dishes and an adhesive-membrane system (A-book). Vacuumed reservoir dust samples were collected from floors at the end of 1 week. Der p 1 was measured in all samples by enzyme-linked immunosorbent assay, except A-books, in which it was measured by Halogen immunoassay.

RESULTS

All four methods intercorrelated moderately (r range = 0.40-0.64, P = 0.04), except between allergen in reservoir dust (as microg/m2 and microg/g dust) and settling dust by Petri dishes (P = 0.2). Reservoir allergen, expressed as microg/m2, did not correlate with any measure, except reservoir allergen expressed as microg/g (r = 0.39, P = 0.04). No differences in these associations occurred between bedrooms and living rooms.

CONCLUSIONS

While the four methods examined correlated moderately, all have practical advantages and difficulties. No method can be considered as ideal for measuring individual exposure. For practicality, use of vacuum cleaner and Petri dish methods are recommended.

Pet-keeping in childhood and adult asthma and hay fever: European community respiratory health survey

BACKGROUND

Whether pet-keeping early in life protects against or promotes allergy remains unclear.

OBJECTIVE

Our aim was to examine the effects of childhood pet-keeping on adult allergic disease in a large international population-based study, including information on sensitization, adult pet-keeping, and pet prevalence in the populations.

METHODS

We used information from structured interviews (n = 18,530) and specific IgE to common aeroallergens in blood samples (n = 13,932) from participants in the European Community Respiratory Health Survey (ECRHS) to analyze the associations between keeping pets and adult asthma and hay fever.

RESULTS

Keeping cats in childhood was associated with asthma only among atopic subjects, an association that varied between centers (P =.002) and was stronger where cats where less common (< 40% cats: odds ratio(wheeze) [OR(wheeze)] = 1.84, 95% CI = 1.31-2.57; 40%-60% cats: OR(wheeze) = 1.33, 95% CI = 1.10-1.61; > or =60% cats: OR(wheeze) = 0.98, 95% CI = 0.73-1.33). Dogs owned in childhood or adulthood were associated with asthma among nonatopic subjects (childhood: OR(wheeze) = 1.28, 95% CI = 1.13-1.46; adulthood: OR(wheeze) = 1.31, 95% CI = 1.14-1.51; both: OR(wheeze) = 1.69, 95% CI = 1.40-2.04). In atopic subjects, those who had owned dogs in childhood had less hay fever (OR = 0.85; 95% CI = 0.73-0.98) and no increased risk of asthma (OR(wheeze) = 1.01, 95% CI = 0.87-1.17). Respiratory symptoms were more common in subjects who had owned birds during childhood (OR(wheeze) = 1.12; 95% CI = 1.02-1.23) independent of sensitization.

CONCLUSIONS

The effects of pet-keeping in childhood varied according to the type of pet, the allergic sensitization of the individual, and the wider environmental exposure to allergen. Cats owned in childhood were associated with more asthma in sensitized adults who grew up in areas with a low community prevalence of cats. Dogs owned in childhood seemed to protect against adult allergic disease but promote nonallergic asthma.

Sensitization to cat allergens in non-cat owner patients with respiratory allergy

BACKGROUND

Cats represent one of the most important sources of indoor allergens. The sensitization rate can reach up to 60% in western countries. Keeping cats indoors is uncommon in big cities in Turkey, but cats living in the streets are common.

OBJECTIVE

To investigate the prevalence of sensitization to cats in patients with respiratory allergy from Izmir, Turkey, and its relationship to home cat allergen levels.

METHODS

A total of 387 patients (70.8% female; mean age, 34.3 years) with respiratory allergic diseases (rhinitis and/or asthma) were included in this study. Skin prick test to cat was performed. House dust samples were collected from the living room of 25 patients and 14 healthy subjects. The major cat allergen (Fel d 1) levels were measured by Dustscreen. Fel d 1 levels given by the manufacturer were as follows: 0.05, 0.13, 0.40, 1.1, and 6.2 mU/mL.

RESULTS

The prevalence of cat sensitivity was 44.7% (n = 173). Only 6 patients (1.6%) had a history of feeding a cat in their houses. Thirty-six (92%) of 39 houses had detectable levels of cat allergen (mean Fel d 1 level, 2.24 +/- 2.69 mU/mL). The mean Fel d 1 levels were 1.58 +/- 2.51 mU/mL in the healthy group, 1.91 +/- 2.61 mU/mL in the asthmatic group, and 3.26 +/- 2.85 mU/mL in the group with allergic rhinitis (P = 0.12). The prevalence of cat sensitivity in patients who had 1.1 mU/mL of Fel d 1 in their homes was 57.1%. This rate was five times lower (11.1%) in patients who had the highest Fel d 1 level (6.2 mU/mL) in their homes.

CONCLUSIONS

The prevalence of cat sensitivity in Izmir, where cats are generally not kept within homes, is as high as in western countries. The sampled houses have measurable levels of Fel d 1 even in the absence of indoor cats. High prevalence of cat sensitivity in Izmir is probably due to indirect exposure.

Early sensitisation and development of allergic airway disease - risk factors and predictors

The development and phenotypic expression of allergic airway disease depends on a complex interaction between genetic and several environmental factors, such as exposure to food, inhalant allergens and non-specific adjuvant factors (e.g. tobacco smoke, air pollution and infections). The first months of life seem to be a particularly vulnerable period and there is evidence that sensitisation is related to the level of allergen exposure during early life. At present, the combination of atopic heredity and elevated cord-blood IgE seems to result in the best predictive discrimination as regards development of allergic disease at birth. Early sensitisation, cow's milk allergy and atopic eczema are predictors for later development of allergic airway disease. Exposure to indoor allergens, especially house dust mite allergens, is a risk factor for sensitisation and development of asthma later in childhood in high-risk infants and infants with early atopic manifestations.

Natural history of asthma

For some children, asthma is a disease whose symptoms seem to remit with time. Numerous children, however, develop disease that is persistent throughout their lifetimes and is associated with more severe symptoms, increased airway reactivity, and loss of lung function. These children typically have a family history of asthma and demonstrate increased airways reactivity and atopy in childhood. A clearer picture of the natural history of asthma in the developing child has been derived from the results of several longitudinal studies. Although some questions have been clarified, several questions still remain. Now that the incidence and severity of asthma seem to be increasing, children born in the last 10 years may experience more severe disease or a different pathophysiology than those born 30 to 40 years ago. New cohort studies are needed to assess this possibility. Additional investigations into the genetics of asthma causation will help elucidate the different phenotypic expressions of this complex disease. Once these different phenotypic groups can be identified early in life, further studies can be performed to explore the impact of therapeutic intervention on the severity of asthma symptoms and loss of lung function.

Heredity, pet ownership, and confounding control in a population-based birth cohort

BACKGROUND

The association between pet ownership in childhood and subsequent allergic disease is controversial. Bias related to selection of pet exposure has been suggested as a reason for contradictory study results.

OBJECTIVE

The purpose of this investigation was to elucidate how pet exposure depends on family history of allergic disease, smoking, and socioeconomic factors in a prospective birth cohort.

METHODS

Parents of 4089 two-month-old children answered a questionnaire that included detailed questions about family history of asthma (maternal, paternal, and sibling), rhinoconjunctivitis, atopic eczema/dermatitis syndrome, pollen and pet allergy, smoking habits, parental occupation, and family pet ownership (cat and dog). Dust samples collected from the mothers' beds were analyzed for Fel d 1 and Can f 1 in a subgroup of the cohort.

RESULTS

Cats were less frequently kept in families with parental asthma, rhinoconjunctivitis, or pet or pollen allergy (3.5% to 5.8%) than in families without parental allergic disease (10.8% to 11.8%). Dogs were less common in families with (3.3%) than in families without (5.9%) parental atopic eczema/dermatitis syndrome. Families with smoking mothers and those with low socioeconomic index kept cats and dogs more frequently. Cat allergen levels were lower in homes with than in homes without maternal pet allergy, and this tended to hold true even for homes without a cat. Cat ownership decreased from birth to 2 years of age, especially in families with parental history of allergic diseases.

CONCLUSION

There seems to be a selection of pet exposure based on parental history of allergy, maternal smoking, and socioeconomic factors. This has to be taken into consideration in evaluations of risk associations between pet exposure and allergic disease in childhood.

The use of mutually exclusive categories for atopic sensitization: a contrasting effect for family size on house dust mite sensitization compared with ryegrass sensitization

Our aim was to examine the relative importance of family size on sensitization to two different allergens: ryegrass and house dust mite (HDM), using a mutually exclusive classification for allergen-specific sensitization. An 8-year follow-up birth cohort study of children born between 1988-89 was conducted. The follow-up sample consisted of 498 children residing in Northern Tasmania in 1997 (84% of eligible). Outcome measures included skin prick test (SPT) reaction to nine aeroallergens and parental questionnaire. Family size was defined as sibling number in 1997. Children with a positive SPT to either Der p or Der f house dust mite but not ryegrass were classified as HDM-exclusive (n = 84). Children with a positive SPT to ryegrass but not HDM were classified as ryegrass-exclusive (n = 43). Family size was associated with reduced ryegrass-exclusive sensitization [AOR 0.57 (0.39, 0.84) per increase in sibling number] but not HDM-exclusive sensitization [AOR 0.97 (0.77,1.23)]. The difference in the family size effect on these sensitization outcomes was significant (p = 0.02). Similarly, family size tended to be associated with reduced asthma among ryegrass-exclusive sensitized children [AOR 0.45 (0.18,1.12)] but not HDM-exclusive sensitized children [(AOR 1.46(0.80-2.65)]. Large family size was strongly associated with reduced sensitization for ryegrass allergens but not HDM allergens using mutually exclusive sensitization categories. If this difference is confirmed in other studies, the contrasting effect of family size may reflect differences between these allergens with regard to level or timing of early life exposure, differences in allergen -specific potentiation for sensitization or unidentified confounding. The use of mutually exclusive categories for allergen sensitization will assist future work on child atopic disease.

Mattress encasings and mite allergen levels in the Prevention and Incidence of Asthma and Mite Allergy study

BACKGROUND

Reduction of allergen exposure from birth may reduce sensitization and subsequent allergic disease.

OBJECTIVE

To measure the influence of mite allergen-impermeable mattress encasings and cotton placebo encasings on the amount of dust and mite allergen in beds.

METHODS

A total of 810 children with allergic mothers took part in the Prevention and Incidence of Asthma and Mite Allergy (PIAMA) study. Allergen-impermeable and placebo mattress encasings were applied to the childrens' and the parents' beds before birth. Dust samples were taken from the beds of children and their parents before birth and 3 and 12 months after birth. Extracts of dust samples were analysed for mite allergens (Der p 1 and Der f 1).

RESULTS

Active mattress encasings were significantly more effective in reducing dust and mite allergen levels than placebo encasings. Mite allergen levels were low in general and the treatment effect was modest. Twelve months after birth, mattresses with active mattress encasings had about half the amount of Der 1 (Der p 1 + Der f 1)/m2, compared to mattresses with placebo encasings, for the child's and the parental mattress.

CONCLUSION

This study shows that mite-impermeable mattress encasings have a significant but modest effect on dust and mite allergen levels of mattresses with low initial mite allergen levels, compared to placebo.

An association between plastic mattress covers and sheepskin underbedding use in infancy and house dust mite sensitization in childhood: a prospective study

BACKGROUND

Higher house dust mite (HDM) allergen exposure during infancy has been associated with increased HDM sensitization. Infant bedding has been associated with the accumulation of varying levels of HDM. Prospective data on the relationship between infant bedding and the development of HDM sensitization has not been previously examined.

OBJECTIVES

To determine if particular types of bedding used in infancy are associated with increased risk of house dust mite sensitization in childhood.

METHODS

A population-based sample (n = 498) of children born in 1988 or 1989, and who were resident in Northern Tasmania in 1997, participated in this study. These children were part of a birth cohort study (1988-95), the Tasmanian Infant Health Survey. Data on infant underbedding and mattresses was available on 460 and 457 children, respectively. The main outcome measure was HDM sensitization defined as a skin prick test (SPT) reaction of 3 mm or more to the allergens of Dermatophagoides pteronyssinus and/or Dermatophagoides farinae.

RESULTS

The use of either sheepskin underbedding or plastic mattress covers in infancy was associated with an increased risk of sensitization to HDM allergens at age 8 years. The adjusted risk ratio (RR) for sensitization to HDM with sheepskin in infancy was 2.27 (95% CI: 1.14, 4.55), P = 0.020. The adjusted RR for sensitization to HDM with the use of plastic mattress covers in infancy was 2.06 (95% CI: 1.22, 3.51), P = 0.007. The use of a foam mattress in infancy was not related to subsequent HDM sensitization.

CONCLUSION

Infant's bedding plays a role in the development of HDM sensitization in childhood. Intervention studies to examine mite allergen levels and the role of underbedding on the development of HDM sensitization are required.

The role of house dust mite elimination in the management of childhood asthma: an unresolved issue

Indoor allergens are likely to be direct environmental causes of asthma and mite exposure, and sensitization is the most important environmental risk factor for childhood asthma in temperate zones. Analagous to occupational asthma, allergen avoidance in asthmatic children sensitized and exposed to mite allergens is associated with a reduction in airway hyperresponsiveness and symptoms associated with improvement in lung function. The long-term effect of this strategy needs to be prospectively evaluated considering both the timing and duration of exposure, as well as the timing and duration of removal. In order to be successful, it is important to achieve and maintain a major reduction on allergen levels, for a long period of time.

[Prevention of asthma and allergic diseases in children]

Allergic diseases have become a major public health problem in industrialized countries, justifying the development of prevention programs. A review of the literature on allergens and atopic symptoms, age of primary sensitization and other factors associated with allergic diseases development is presented and is followed by a discussion on prevention measures. The most recent physiopathological and immunological data indicate that persistent asthma and allergic diseases in adults may be associated with events in early childhood. The parallel increase in autoimmune and allergic diseases has been correlated with regulatory mechanism defects, contradicting the previous theory that involved a predominantly Th1 or Th2 pathway. The primary prevention of asthma and allergic diseases thus appear to be somewhat utopian. Indeed based on recent results, the risk of developing allergies appears to be related to modern "clean" lyfestyles. Secondary prevention is probably necessary, possibly through specific immunotherapy. Tertiary prevention must also be considered. Passive smoking must be prevented as it can alter the development of the respiratory system and promote allergen sensitization. Randomized, controlled, prospective studies are needed to evaluate the efficacy of the preventive measures.

Early pet exposure: friend or foe?

PURPOSE OF REVIEW

Sensitization to pets is a risk factor for asthma and it was assumed that pet ownership was a risk factor for sensitization. Epidemiological studies failed to confirm this, some even suggesting that keeping pets decreased the risk of sensitization and asthma. In the last year, 10 studies have been published which have, at least in part, attempted to address the question. The results, however, are heterogeneous and it is still not clear how we should advise our patients on this issue of pet ownership.

RECENT FINDINGS

Results of studies of the association between exposure to cat or cat allergen and the development of sensitization are such that almost any view on the relationship could be supported by evidence from the literature. For dogs, there are fewer data, but there is little to suggest that keeping a dog increases the risk of sensitization to dog. The majority of studies reviewed find either no association or a reduced risk of asthma amongst pet owners, but only one of these selectively excludes those who deliberately avoid pets from the analysis. There is evidence to suggest that amongst non-pet owners, the risk of sensitization and of asthma increases in areas with a high proportion of pet owners. There is evidence emerging that the effect of exposure to pets may be different in different relative risk groups, based on parental allergy. There is also evidence that asthma is more severe amongst pet sensitized pet owners.

SUMMARY

There are several large birth cohort studies being conducted around the world designed to measure the development of asthma and allergies in children with prospective and objective measures of environmental exposures. The results of such studies are required before the association between pets and asthma can be determined.

Familial and environmental determinants for wheezing and asthma in a case-control study of school children in Palestine

BACKGROUND

Our prevalence study on Palestinian school children aged 6-12 years showed lower rates for asthma and asthma symptoms than economically developed and industrialized countries. Reasons for such differences are largely unknown, and could possibly be related to different environmental and lifestyle factors.

OBJECTIVE

To investigate familial, early life exposures and indoor environmental determinants for asthma in children in Palestine.

METHODS

From the population of our previous study, a group of 273 children with wheeze in the past 12 months (of whom 99 children had physician-diagnosed asthma) were matched with an equal number of non-wheezing controls. This case-control study involved a parental questionnaire; skin prick testing (SPT) with mixed house dust mites, cat and dog dander, mixed grass, mixed trees pollen, Alternaria tenuis, olive tree and cockroach extracts; and serum for total and specific IgE for the same eight allergens.

RESULTS

Paternal asthma and maternal hayfever significantly tripled the risk for their children to have wheezing. Previous diagnoses of bronchial allergy, bronchitis, pneumonia, or whooping cough, and positive SPT for house dust mites and cockroaches were significantly more likely among wheezing and asthmatic children than controls. Specific IgE levels for house dust mites and cat allergens showed significantly higher risk for reported wheezing. After adjustment for several environmental and sociodemographic factors using multivariate logistic regression analysis, paternal asthma, maternal hayfever, damp houses, cat and cockroach SPT positivity proved to be strong predictors for wheezing symptoms.

CONCLUSION

Our study confirmed that familial 'atopic' diseases are significant predictors of childhood asthma in Palestinian children. Moreover, indoor environment such as presence of cats and domestic moulds also appear to play a role. Our findings are consistent with studies in Canada, New Zealand, Estonia and Sweden, and show promise to explore further gene-environment interaction in the genesis of asthma.

Current mite, cat, and dog allergen exposure, pet ownership, and sensitization to inhalant allergens in adults

BACKGROUND

Simultaneous exposure to more than one allergen might modify the effect of individual allergens.

OBJECTIVE

The purpose of this study was to investigate the effect of current exposures to mite, cat, and dog allergen and pet ownership on sensitization in adults.

METHODS

Questionnaires, skin tests, and home visits (Der p 1, Fel d 1, and Can f 1, ELISA; mattresses, living room floors) were performed in 2502 adults. Allergen exposure was treated as a continuous variable and divided into quartiles. To investigate the interaction between allergens, quartiles for 3 allergens were added, creating arbitrary combined exposure categories.

RESULTS

In the univariate analysis, mite sensitization was associated with Der p 1 in mattresses (odds ratio [OR], 1.10; 95% CI, 1.01 to 1.19; P =.03) and with Can f 1 in living room floors (OR, 1.08; 95% CI, 1.00 to 1.17; P =.05). In a multivariate regression analysis, Der p 1 in mattresses remained an independent associate of mite sensitization (OR, 1.12; 95% CI, 1.02 to 1.23; P =.03) and pollen sensitization (OR, 1.23; 95% CI, 1.11 to 1.36; P =.0001). The proportion of subjects sensitized to mite increased significantly with the increasing combined exposure categories (P <.0001). The highest prevalence of sensitization to cat and dog was in the medium combined exposure categories. Cat ownership was associated with a reduced prevalence of sensitization to cats (P =.002) and a reduced prevalence of sensitization to dog (P =.003) but had no effect on sensitization to mite and pollen.

CONCLUSIONS

Sensitization to dust mites increased with the increasing combined exposure. Cat ownership was associated with a lower prevalence of sensitization to cat and dog but not to mite and grass pollen.

Health impacts of second-hand exposure to cat allergen Fel d 1 in infants

BACKGROUND

Recent cross-sectional studies suggested that highest sensitization prevalences occur with moderate cat allergen exposures. We aimed to assess the impact of moderate levels of second-hand cat allergen exposure on the incidence of specific sensitization and wheezing in the framework of a birth cohort study. Therefore we restricted our analysis to infants without a cat at home since birth.

METHODS

At infant's age 3 months, cat allergen levels were measured in the mattress dust of 1840 families without cats. At age 2 years, serum IgE specific to Fel d 1 was analyzed. Incidence of wheezing apart from respiratory infection was assessed by questionnaire. Logistic regression models were used to calculate adjusted odds ratios (OR) for the association between second-hand cat allergen exposure and health outcomes.

RESULTS

Until age 2 years, 13 of 1301 infants (1%) were sensitized to cat allergen and 56 of 1492 infants (4%) had ever-wheezing without infection. Early exposure to second-hand cat allergen levels >or= 1 microg/g dust increased substantially the risk for specific sensitization to Fel d 1 (OR 10.9, 95% CI 3.4-35.0) and ever-wheeze without infection (OR 2.0, 95% CI 1.1-3.9) at age 2 years.

CONCLUSIONS

Second-hand exposure to cat allergen in homes without cats is detrimental in terms of allergy development in infants.

House dust mite allergen in US beds: results from the First National Survey of Lead and Allergens in Housing

BACKGROUND

Although exposure to house dust mite allergen is a major risk factor for allergic sensitization and asthma, nationwide estimates of dust mite allergen levels in US homes have not been reported.

OBJECTIVE

The purpose of this study was to estimate the prevalence of dust mite allergen in beds of US homes and to identify predictors of dust mite allergen concentration.

METHODS

Data were obtained from the first National Survey of Lead and Allergens in Housing, a cross-sectional survey of 831 permanently occupied noninstitutional housing units that permitted resident children. Dust mite allergen concentration (Der f 1 plus Der p 1) was determined from a dust sample collected from a bed. The percentages of homes with concentrations at or greater than detection, 2.0 microg/g bed dust, and 10.0 microg/g bed dust were estimated. Independent predictors of allergen concentration were assessed with multivariable linear regression.

RESULTS

The percentages of US homes with dust mite allergen concentrations at or greater than detection, 2.0 microg/g, and 10.0 microg/g were 84.2% (SE, 1.73), 46.2% (SE, 2.0), and 24.2% (SE, 2.1), respectively. Independent predictors of higher levels were older homes, non-West census regions, single-family homes, no resident children, lower household income, heating sources other than forced air, musty or mildew odor, and higher bedroom humidity.

CONCLUSION

Most US homes have detectable levels of dust mite allergen in a bed. Levels previously associated with allergic sensitization and asthma are common in US bedrooms. Predictors can be used to identify conditions under which homes are more likely to have increased dust mite allergen levels.

Synthetic bedding and wheeze in childhood

BACKGROUND

The reasons for the increase in childhood asthma over time are unclear. The indoor environment is of particular concern. An adverse role for synthetic bedding on asthma development in childhood has been suggested by cross-sectional studies that have found an association between synthetic pillow use and childhood wheeze. Prospective data on infant bedding have not been available.

METHODS

Bedding data at 1 month of age were available from an infant survey for children who were participating in a 1995 follow-up study (N = 863; 78% traced). The 1995 follow-up was embedded in a larger cross-sectional survey involving 6,378 seven year olds in Tasmania (N = 92% of eligible). Outcome measures included respiratory symptoms as defined in the International Study of Asthma and Allergies in Childhood protocol. Frequent wheeze was defined as more than 12 wheeze episodes over the past year compared with no wheeze.

RESULTS

Synthetic pillow use at 1 month of age was associated with frequent wheeze at age 7 (adjusted relative risk [aRR] = 2.5; 95% confidence interval [CI] = 1.2-5.5) independent of childhood exposure. Current synthetic pillow and quilt use was strongly associated with frequent wheeze (aRR = 5.2; CI = 1.3-20.6). Substantial trends were evident for an association of increasing number of synthetic bedding items with frequent wheeze and with increasing wheeze frequency. Among children with asthma, the age of onset of asthma occurred earlier if synthetic bedding was used in infancy.

CONCLUSIONS

In this cohort, synthetic bedding was strongly and consistently associated with frequent childhood wheeze. The association did not appear to be attributable to bedding choice as part of an asthma management strategy.

The impact of climate change on child health

Human activity has contributed to climate change. The relationship between climate and child health has not been well investigated. This review discusses the role of climate change on child health and suggests 3 ways in which this relationship may manifest. First, environmental changes associated with anthropogenic greenhouse gases can lead to respiratory diseases, sunburn, melanoma, and immunosuppression. Second, climate change may directly cause heat stroke, drowning, gastrointestinal diseases, and psychosocial maldevelopment. Third, ecologic alterations triggered by climate change can increase rates of malnutrition, allergies and exposure to mycotoxins, vector-borne diseases (malaria, dengue, encephalitides, Lyme disease), and emerging infectious diseases. Further climate change is likely, given global industrial and political realities. Proactive and preventive physician action, research focused on the differential effects of climate change on subpopulations including children, and policy advocacy on the individual and federal levels could contain climate change and inform appropriate prevention and response.

Pets in the home and the development of pet allergy in adulthood. The Copenhagen Allergy Study

BACKGROUND

The aim of the study was to investigate the association between exposure to cat and dog in the home and the development (incidence) of IgE sensitization to cat and dog.

METHODS

Participants in a population-based study of 15-69-year-olds in 1990 were invited to a follow-up in 1998. Serum IgE antibodies against common inhalant allergens was assessed in 734 subjects (participation rate 69.0%) on two occasions 8 years apart. Information about current or previous keeping of cats and dogs in the home was obtained in a questionnaire at baseline.

RESULTS

A cat in the home currently was significantly associated with the development of IgE sentisization to cat (adjusted odds ratio 8.4, 95% confidence interval (CI) 1.7-42.7). Moreover, an atopic predisposition in terms of IgE sensitization to allergens other than cat at baseline was an independent risk factor for the development of IgE sensitization to cat. A dog in the home was not significantly associated with the development of IgE sensitization to dog.

CONCLUSIONS

In this adult population, exposure to a cat in the home increased the risk of developing IgE sensitization to cat. More prospective data are needed on this issue.

Allergen sensitization and allergen exposure in Greenlander Inuit residing in Denmark and Greenland

The aim of this study was to estimate the prevalence of allergic sensitization and possible risk factors in a genetically homogenous Inuit population living under widely differing climatic and cultural conditions. A written questionnaire and skin prick test for 10 aeroallergens were obtained from 1119 adult Greenlanders residing in Denmark, Nuuk (main city in Southern Greenland) and Uummannaq (rural settlement in Northern Greenland). Allergen exposure was assessed by pollen counts, questions on pet keeping and counts of house dust mites in dust samples. The overall prevalence of at least one positive skin prick test was 22.8% in Denmark, 10.6% in Nuuk, and 6.4% in Uummannaq. In Denmark, the total birch pollen counts were 40-1000 times higher compared to Nuuk, whereas the grass pollen count was 13-30 times higher in Denmark compared to Nuuk. Dogs were held indoor with a similar frequency in Denmark and Nuuk, but much less frequently in Uummannaq. In Denmark, house dust mites were found in 72% of house holds (>10/0.1 g dust). Less than 15% of households in Greenland had measurable levels of house dust mites. The prevalence of sensitization to aeroallergens in Inuit Greenlanders differed significantly between Denmark, Nuuk and Uummannaq. These findings correlated with the observed differences in population allergen exposure in the three regions. Furthermore, differences in lifestyle factors such as educational level, stress and ethnic self-identification seemed to be associated with the risk of allergic sensitization in Greenland.

Exposure to pets and atopic dermatitis during the first two years of life. A cohort study

The aim of this study was to assess the association between keeping pets in early childhood and the occurrence of atopic dermatitis in an ongoing birth cohort followed up to the age of 2 years. We analyzed data of 4578 children in the intervention and observation part of an ongoing cohort study. The children were recruited at birth in the two study regions Wesel and Munich between January 1996 and June 1998. Information on atopic diseases and pet ownership was obtained by questionnaire at the child's first and second birthday. The logistic regression model showed a negative association between 'keeping any pet' and in particular 'keeping dogs' in the 1st year of life and the development of atopic dermatitis in the 1st and the 2nd years of life. The protective effects remained statistically significant after adjusting for several possible confounding variables (1st year(any) pet OR 0.71, 95% CI [0.55;0.92], 1st year(dog) OR 0.62, 95% CI [0.39;0.98], 2nd year(any) pet OR 0.74, 95% CI [0.57;0.97], 2nd year(dog) OR 0.63, 95% CI [0.40;0.98]). Ownership of small furred pets (hamster, rabbit and guinea pig) also showed a borderline protective effect for the 1st year. We assume an association between keeping pets and undefined environmental factor(s) that contribute protectively to the development of atopic dermatitis in early life, presumably by effects on the maturation of the immune system.

Domestic aeroallergen levels in Barcelona and Menorca (Spain)

Exposure to common indoor allergens is known to be associated with sensitization and triggers of asthma. Levels of allergens have been barely described in Mediterranean countries. This study reports domestic allergen levels among the general population of two regions of Spain. Dust samples were collected from living rooms and mattresses in homes of infants in Barcelona (n = 366) and Menorca (n = 475) and assayed for house dust mite (Der p 1) and cat allergen (Fel d 1) concentrations by enzyme-linked immunoabsorbent assay (ELISA). Geometric mean values (95% CI) of Der p 1 were 0.77 micro g/g (0.65, 0.92) in living rooms and 0.68 (0.56, 0.82) in children's mattresses in Barcelona, and 9.06 (7.93-10.34) and 3.12 (2.71-3.59) in Menorca, respectively. Fel d 1 levels were 0.37 micro g/g (0.31, 0.45) and 0.14 (0.12, 0.18) in Barcelona, and 0.42 (0.35, 0.50) and 0.20 (0.18, 0.24) in Menorca. Home characteristics were not consistently related to levels of aeroallergens in either location. Differences in Der p 1 levels in the two locations indicate that levels cannot be extrapolated from one part of a country to another with any certainty. Additionally, allergen reduction measures related to indoor sources must be specific to each location.

House dust mite allergen levels in German day-care centers

We investigated the levels of the major house dust mite allergens, Der p 1 and Der f 1, in dust collected from various locations in 41 day-care centers from two German cities (Düsseldorf and Bonn). One hundred and thirty-seven (96%) of 143 samples yielded detectable amounts of house dust mite allergen (range, < 15-85,000 ng/g; interquartile range, 210-1,480 ng group I allergen [sum of Der p 1 and Der f 1]/g dust), and 24 (17%) of the samples (8/34 mattresses; 11/46 cushions/soft toys; 5/43 carpeted floors, 0/20 smooth floors) exceeded the proposed "threshold" level of 2,000 ng/g dust in 18 (44%) of 41 day-care centers. Der p 1 and Der f 1 could be detected in nearly an equal number of samples. The highest concentrations of house dust mite allergens were found in dust from mattresses (geometric mean, 1,103 ng/g dust) and cushions/soft toys (geometric mean, 1,004 ng/g dust). The allergen load per unit area from carpeted floors exceeded that from smooth floors by more than two orders of magnitude. In comparison with dust samples from private homes within the same geographical area, the mite allergen levels in mattress dust (RR, 0.34; CI95, 0.18-0.64) and floor dust (RR, 0.21; CI95, 0.09-0.49) from day-care centers were significantly lower (p < 0.001). We conclude that day-care centers should be included as potential places of additional exposure to house dust mite allergens if avoidance measures are taken.

Environmental exposure to endotoxin and its relation to asthma in school-age children

BACKGROUND

In early life, the innate immune system can recognize both viable and nonviable parts of microorganisms. Immune activation may direct the immune response, thus conferring tolerance to allergens such as animal dander or tree and grass pollen.

METHODS

Parents of children who were 6 to 13 years of age and were living in rural areas of Germany, Austria, or Switzerland where there were both farming and nonfarming households completed a standardized questionnaire on asthma and hay fever. Blood samples were obtained from the children and tested for atopic sensitization; peripheral-blood leukocytes were also harvested from the samples for testing. The levels of endotoxin in the bedding used by these children were examined in relation to clinical findings and to the cytokine-production profiles of peripheral-blood leukocytes that had been stimulated with lipopolysaccharide and staphylococcal enterotoxin B. Complete data were available for 812 children.

RESULTS

Endotoxin levels in samples of dust from the child's mattress were inversely related to the occurrence of hay fever, atopic asthma, and atopic sensitization. Nonatopic wheeze was not significantly associated with the endotoxin level. Cytokine production by leukocytes (production of tumor necrosis factor alpha, interferon-gamma, interleukin-10, and interleukin-12) was inversely related to the endotoxin level in the bedding, indicating a marked down-regulation of immune responses in exposed children.

CONCLUSIONS

A subject's environmental exposure to endotoxin may have a crucial role in the development of tolerance to ubiquitous allergens found in natural environments.

Do allergens play a role in early childhood asthma?

What we know: Sensitisation to indoor allergens (house-dust mite, cat) is related to the level of exposure to these allergens in early childhood. The prevalence of asthma in childhood is independent of allergen exposure in early life. Asthma occurs in a substantial number of young children in the absence of allergen sensitisation. Asthma and allergic sensitisation have increased in recent decades, but there is no conclusive evidence that this is due to changes in environmental allergens. What we need to know: Have changes in environmental allergens contributed to the increasing incidence of asthma in recent decades? Is early childhood asthma (or certain subtypes of asthma) an allergen-induced disease? Is it possible to modify asthma by environmental allergen manipulation in early childhood? Is it possible to modulate the immune response to allergens in a favourable direction in early childhood?

Dust mite allergens: mitigation and control

In recent years, greater attention has been given to the role of indoor allergens as a cause of sensitization and allergic respiratory diseases. Although indoor allergen control measures to reduce symptoms in individuals allergic to mites have produced controversial results, environmental allergen avoidance is today one of the four primary goals of asthma management recommended in several guidelines of asthma treatment. Exposure to high indoor aeroallergen levels, especially to house dust mite allergens, is an important environmental risk factor for allergic sensitization and the subsequent development and exacerbation of asthma. Therefore, effective aeroallergen avoidance is of use to prevent and treat allergic diseases. Although endotoxin exposure may be protective in early life, it has been demonstrated that the inhalation of endotoxin may exacerbate asthma in house dust mite sensitized patients. Mite-allergic asthmatic patients should be aware of the dangerous combination of mite allergen exposure associated with high endotoxin levels in house dust. These two immunologically active substances have been associated with severe asthma and seasonal exacerbation of symptoms. Effective house dust mite allergen avoidance will never be achieved using a single control measure; various methods are required to affect the multiple factors that facilitate high indoor allergen levels. Education of the patients and their families is also an important component of environmental control strategies.