Asthma severity and morbidity in a population sample of Sydney schoolchildren: Part II--Importance of house dust mite allergens

Asthma Control and Its Predictive Factors in Adult Asthma Patients

BACKGROUND

Asthma is a highly prevalent condition that remains difficult to control, as its associated factors remain poorly understood. Thus, the primary aim of the present investigation was to determine the prevalence of uncontrolled asthma in hospital units in south Jordan and to evaluate the risk factors that may contribute to uncontrolled asthma.

METHODS

This was a cross-sectional study involving 93 patients aged 40.5 ± 13.6 years that met the criteria of the Global Initiative for Asthma (GINA). Relevant patient data were collected via a questionnaire and through a review of medical records. The questionnaire comprised of sections pertaining to sociodemographic and clinical characteristics, as well as pharmacological asthma treatment, asthma severity and asthma control. Asthma severity was determined in line with the GINA guidelines, whereby the patients were classified into four groups (intermittent, mild persistent, moderate persistent or severe persistent). Moreover, based on the findings yielded by the asthma control questionnaire (ACQ), patients were divided into three levels, whereby those diagnosed with partly controlled and uncontrolled asthma were combined into one group, denoted as "poorly controlled asthma", with "uncontrolled asthma" and "controlled asthma" as the remaining two groups. Atopy was defined as one or more positive reactions (A/H ratio > 1) on a skin prick test.

RESULTS

Asthma control was achieved in 45.2% of the sample. Moreover, older age, severe asthma according to the GINA guidelines, longer duration of asthma, atopy, being on treatment for asthma and history of allergic rhinitis were identified as the main risk factors contributing to poorly controlled asthma. Multivariate analyses, however, revealed that only atopy to two or more allergens and having severe asthmatic attacks were statistically significantly associated with poorly controlled asthma, for which the odds ratio Mantel-Haenszel (ORMH) of 17.2 and 2.2 was obtained, respectively.

CONCLUSION

Our findings indicate that severe asthma and atopy to two or more allergens are the main risk factors for uncontrolled asthma. However, further studies with larger sample sizes are needed to confirm these results.

Skin test reactivity of allergic subjects to basidiomycetes' crude extracts in a tropical environment

Fungal allergies can be detected by the skin prick test with extracts of the organisms, but not all fungi, including the basidiomycetes, are being examined. We determined the level of sensitization to basidiomycetes in allergic subjects and compared their reactivity to commercial extracts commonly used to detect allergies. Crude spore extracts of the basidiomycetes Ganoderma applanatum, Chlorophyllum molybdites, and Pleurotus ostreatus, which are known to release numerous spores, were examined along with commercial extracts on 33 subjects with asthma, allergic or non-allergic rhinitis. Overall, affected subjects showed the highest reactivity to mites (36%), followed by Ganoderma applanatum (30%), grass (27%) Chlorophyllum molybdites (12%) and Pleurotus ostreatus (12%). Allergic rhinitis patients were most reactive to mites (58%), grass (42%), Ganoderma applanatum (25%), Penicillium spp. (25%), and cat (17%). Those with asthma primarily responded to mites (44%), Ganoderma applanatum (44%), grass (33%), and Pleurotus ostreatus (22%). IgE levels correlated with positive basidiomycetes extracts. This finding, coupled with higher reactivity to basidiospores as compared to mitospores, and the similar sensitivities of patients to G. applanatum and mites, suggest that basidiomycetes are important allergen sources in the tropics.

Utility of hypertonic histamine challenge in distinguishing difficult-to-diagnose asthma

INTRODUCTION

Although classical asthma is associated with airway hyperresponsiveness (AHR), this condition is also present in many cardiopulmonary disorders undermining the rational basis of its measurement in the differential diagnosis of asthma. We have recently introduced a new method to investigate AHR, the hypertonic histamine challenge (HHC).

OBJECTIVE

The aim of this study was to evaluate the differential diagnostic power of HHC in a clinically representative sample of 138 patients.

METHODS

Fifty-seven patients from the outpatient clinic of the authors' hospital with symptoms indicative of asthma were consecutively recruited. Asthma was confirmed in 31 subjects. The remaining 26 subjects formed the control group, in conjunction with seven patients with COPD, 15 patients with interstitial lung disease, 21 patients with rhinitis, 13 patients with heart failure and 25 healthy controls. Hypertonic histamine solution was administered with an ultrasonic nebuliser.

RESULTS

Only the PC(20) values of asthmatic subjects differed statistically significantly from those of the healthy group (P < 0.0001). The receiver operator characteristic curve indicated that a PC(20) value of 0.83 mg/mL would be the optimal cut-off point of HHC to separate the asthmatics from the symptomatic controls with a sensitivity of 81% and specificity of 70%. With the PC(20) values of 0.1 and 4.0 mg/mL, the sensitivities were 42% and 100%, and the specificities were 96% and 40%, respectively. In these limits, HHC either confirmed or excluded asthma in 64 out of 138 patients (46%).

CONCLUSION

The authors' attempt to improve the accuracy of the airway challenge test by combining direct and indirect challenges did not overcome the diagnostic limitations of previously utilised airway challenges.

IL-5 T-cell responses to house dust mite are associated with the development of allergen-specific IgE responses and asthma in the first 5 years of life

BACKGROUND

Allergen-specific T(H)2-like cytokine responses are considered to be important in sensitization and allergic diseases.

OBJECTIVE

To examine the profile of house dust mite (HDM) stimulated T-cell cytokines and their relationship to allergic disease in children over the period of the first 5 years of life.

METHODS

Subjects with a family history of asthma who were enrolled antenatally in the Childhood Asthma Prevention Study and had skin prick tests, clinical evaluation for asthma and eczema, and in vitro assessment of lymphocyte cytokine responses to HDM extract performed at ages 18 months (n = 281), 3 years (n = 349), and 5 years (n = 370). IL-13 at 3 and 5 years and IL-5, IL-10, and IFN- gamma at 18 months, 3 years, and 5 years were measured by ELISA.

RESULTS

House dust mite-specific cytokine responses increased with age for all cytokines except IFN-gamma. HDM-specific IL-5 responses at 3 years and 5 years were significantly positively related to skin prick test positivity at 5 years. IL-5 responses at 5 years were also significantly related to asthma at 5 years. Other HDM-specific cytokine responses were not related to asthma or eczema at 5 years. Responses were not altered by a HDM avoidance intervention.

CONCLUSION

IL-5 responses to HDM, the dominant local inhalant allergen, are related to the expression of clinical illness at age 5 years.

CLINICAL IMPLICATIONS

The T-cell response to HDM, as reflected in IL-5 production, is acquired over the first years of life and may play a role in the expression of allergic airways disease.

Maternal influence in the transmission of asthma susceptibility

Asthma is one of the most common chronic diseases in children, with increasing morbidity and mortality. A genetic predisposition and exposure to allergens have been implicated as major risk factors for the development of asthma. However, increasing evidence indicates that the mother plays a crucial role in mediating the development of fetal-infant immune responses to inhaled allergens. The exact nature and mechanism of this maternal influence and how it might be associated with the development of allergic sensitization and asthma are not clear. Under normal conditions, the maternal environment during pregnancy promotes an initial Th2 skewed immune response in the offspring which transitions to a nonallergic Th1 type response after birth. However, the allergic mother's influence may delay the normal transition to a nonallergic immune response to inhaled allergens in her children, thus increasing the risk for the development of allergic sensitization and/or asthma. Understanding the underlying mechanisms by which the maternal immune environment can influence the development of the fetal-infant immune response to inhaled allergens may lead to identifying new targets for the prevention of allergic sensitization and asthma.

Air pollution, weather, and associated risk factors related to asthma prevalence and attack rate

Asthma is an important public health challenge. The objective of this research was to investigate the relationship of air pollution and weather to adolescent asthma prevalence and attack rate. A 6-month mass screening asthma study was conducted from October 1995 to March 1996 in Taiwan. The study population included junior high school students from throughout the country (1,139,452 students). Eighty-nine percent of students completed questionnaires (International Study of Asthma and Allergies in Childhood-ISAAC and New England Core Questionnaires) and passed a logical screening error program. Lung function data was collected to assist in the diagnosis of asthma status. From the students screened during this mass survey, a stratified random sample of 64,660 students was analyzed for asthma prevalence and attack rate. Using a regression model to compare the USEPA National Ambient Air Quality Standards 2000 (NAAQS, 2000) to asthma prevalence, this investigation found that the standards may not provide enough protection for adolescents after controlling for age, rhinitis, eczema, urban birth location, parental education level, exercise, cigarette smoking, environmental tobacco smoking, alcohol beverage consumption and weather factors. The general estimating equations (GEE) model, a repeated measurement regression model, was used to examine the relationship between the monthly asthma attack rate among asthma patients and air pollution (nitrogen oxides; nitrogen dioxide; nitric oxide; Ozone; PM10) while controlling for household smoking. The GEE model demonstrated that air pollution is related to asthma attack rate. Air pollution factors also interacted with weather parameters when related to asthma attack rate.

Asthma severity and atopy: how clear is the relationship?

BACKGROUND

The relationship between asthma severity and atopy is complex. Many studies have failed to show significant relationships between clinical severity or lung function and markers of atopic sensitisation.

AIM

To determine whether increasing asthma severity is related to atopic sensitisation in a population of children with asthma.

METHODS

A total of 400 children (7-18 years) with asthma were recruited as part of a multicentre study of the genetics of asthma. Detailed phenotypic data were collected on all participants. Associations between measures of asthma severity and atopic sensitisation were sought using multilevel models allowing variation at the individual and family level.

RESULTS

Children recruited to the study had a range of asthma severities, with just over a third having mild persistent asthma. The logarithm of total serum IgE was associated with increased asthma severity score, decreased FEV1, increased airways obstruction, risk of hospital admission, and inhaled steroid use. Increasing skin prick test reactivity to a panel of seven aeroallergens was associated with increased risk of hospital admission, use of an inhaled steroid, and airways obstruction. The results remained highly significant after corrections for age, gender, and birth order.

CONCLUSIONS

In children with asthma, increasing atopy is associated with increasing asthma severity. However, the relationships between asthma severity and skin prick tests, and asthma severity and total serum IgE values, appear subtly different.

Efficacy and safety of allergen immunotherapy in children

OBJECTIVE

To determine the efficacy and safety of immunotherapy in children with allergic rhinitis and allergic asthma.

DATA SOURCES

Current Contents database for 1967 to 2005.

STUDY SELECTION

The expert opinion of the author was used to select studies for inclusion in this review.

RESULTS

Meta-analyses have confirmed the clinical effectiveness of allergen immunotherapy in patients with allergic rhinitis and asthma; however, most studies involved immunotherapy with a single allergen. Special considerations of safety regarding immunotherapy in children are also necessary, since fatalities have been reported. Fatal reactions occur primarily in patients with asthma and particularly those whose asthma is not well controlled. There is probably increased risk during the build-up phase and with the first injection from a new vial. Injections at home or in clinics without adequate supervision also constitute an increased risk of a fatal outcome.

CONCLUSIONS

Specific immunotherapy has been demonstrated to have some protective effect against the development of additional sensitivities in the monosensitized child and to reduce the risk of developing asthma in children with allergic rhinitis. Because of the modification of the underlying immune process, the beneficial effects of immunotherapy persist for a long but not yet fully determined period after the cessation of treatment. This persisting effect makes immunotherapy an attractive supplement to symptomatic treatment of children with allergic asthma and allergic rhinitis. The treatment is not without risk, however, especially in the child with asthma, so it should be administered with caution.

Infant sleeping environment and asthma at 7 years: a prospective cohort study

OBJECTIVES

We investigated the role of infant bedding items, as part of a composite bedding environment, in the development of childhood wheezing.

METHODS

This prospective cohort investigation involved 863 children who participated in an infant survey in 1988 and an asthma study in Tasmania, Australia, in 1995. The derived 3 composite infant bedding categories corresponded to increasing numbers of house dust mite (HDM)-rich bedding items used. Outcomes measured included recent and frequent wheezing.

RESULTS

Composite infant bedding used was associated with recent wheezing. Effects increased at increasing levels of HDM-rich bedding items used. Effects were further enhanced by home environmental factors of bedroom heating, recent bedroom painting, and absence of bedroom carpeting. When any 2 or more of these environmental factors were present, a strong dose-response relationship was evident.

CONCLUSIONS

Our results show that bedding exposures in infancy are prospectively associated with childhood wheezing and that home environmental conditions may modify this association.

Atopy and house dust mite sensitization as risk factors for asthma in children

Asthma is commonly described as an atopic disease in childhood, but some cases of this disorder do not fit this description. The aim of this study was to evaluate the frequency of atopy, asthma, and sensitization to house dust mites in children with allergic symptoms. This study was performed at the Severance Hospital of Yonsei University with patients who visited the allergy clinic for evaluation of nonspecific upper respiratory symptoms, typical symptoms of asthma, or a general health workup. The patients were divided into three age groups: 0-3 years (group 1), 4-7 years (group 2), and 8-12 years (group 3). Of the 1,244 children examined, 844 (67.8%) were atopic and 400 (32.2%) were non-atopic. The frequency of atopy and asthma increased with age. Asthma was diagnosed in the same proportion (64%) of atopic and non-atopic children. As risk factors for asthma symptoms, the positive values of house dust mite (HDM) sensitivity were significantly increased in groups 1, 2, and 3 to 53.5%, 68.9%, and 80.2%, respectively. A significant difference between the percentage of asthmatics sensitized to HDM and that of asthmatics not sensitized to HDM was found only in group 3. In conclusion, asthma is related to atopy with increasing age, and house dust mite sensitization seems to be an important determinant of asthma in older children in Korea.

The bedding environment, sleep position, and frequent wheeze in childhood

OBJECTIVE

Synthetic quilt use has been associated with increased childhood wheeze in previous studies. Our aim was to examine whether the adverse effect of synthetic quilt use on frequent wheeze differed by usual sleep position.

DESIGN, SETTING, AND PARTICIPANTS

A population-based cross-sectional study of 6378 (92% of those eligible) 7-year-olds in Tasmania, Australia, was conducted in 1995. Exercise-challenge lung function was obtained on a subset of 414 children from randomly selected schools.

EXPOSURE MEASURES

Child bedding including pillow and overbedding composition and usual sleep position by parental questionnaire.

OUTCOME MEASURES

Frequent wheeze (>12 wheeze episodes over the past year), using the International Study of Asthma and Allergies in Childhood parental questionnaire, and baseline and postexercise forced expiratory volume in 1 second lung-function measures.

RESULTS

Frequent wheeze (n = 117) was positively associated with synthetic quilts, synthetic pillows, electric blankets, and sleeping in a bottom bunk bed but did not vary by sleep position. In a nested case-control analysis, the association between synthetic quilt use and frequent wheeze differed by sleep position. Among children who slept supine, synthetic (versus feather) quilt use was associated with frequent wheeze (adjusted odds ratio: 2.37 [1.08, 5.23]). However, among nonsupine sleepers, overlying synthetic quilt use was not associated with frequent wheeze (adjusted odds ratio: 1.06 [0.60, 1.88]). This difference in quilt effect by sleep position was highly significant. Similarly, synthetic quilt use was associated with lower postexercise forced expiratory volume in 1 second measures among supine but not nonsupine sleeping children.

CONCLUSION

An increasing focus on the bedding environment immediately adjacent to the nose and mouth is required for respiratory disorders provoked by bedding, such as child asthma characterized by frequent wheeze.

Association of recurrent wheezing with sensitivity to cockroach allergen in inner-city children

BACKGROUND

There are numerous data that show a strong relationship between early exposure and sensitization to indoor allergens and the development of asthma and persistent wheezing in children. Most studies, however, have only examined the prevalence of allergy in children who have been identified as having asthma.

OBJECTIVE

To assess the prevalence of positive skin test results to common inhaled allergens and possible association with wheezing in inner-city children being seen in a general pediatric clinic.

METHODS

Skin testing to common aeroallergens was performed by the prick-puncture method. Demographic and clinical data were collected.

RESULTS

Seventy-five children aged 2 months to 10 years were evaluated. A total of 37% of the children had a positive skin test result to at least one allergen; 29% of the children were sensitive to dust mite, 15% to cockroach, 9% to cat, 7% to mold, 4% to grass, 3% to ragweed, and 1% to dog. Seven (64%) of 11 children with positive skin test results to cockroach had a history of wheezing compared with 21 (33%) of 64 with negative skin test results to cockroach (P = .05).

CONCLUSIONS

Our results indicate that in a population of inner-city children not previously identified as atopic, more than a third showed sensitivity to at least one allergen. Although dust mite was the most common allergen to which the children were sensitized, cockroach sensitivity was the only allergen that correlated significantly with previous episodes of wheezing.

Parental allergic status influences the risk of developing allergic sensitization and an asthmatic-like phenotype in canine offspring

Increasing evidence suggests that parental allergic status, especially that of the mother, may play a unique and important role in influencing the development of fetal infant immune responses to inhaled allergens, independently of genetic predisposition. We have developed an experimental model in dogs where the offspring from allergic parents, when exposed to inhaled allergen, develop allergic sensitization and an asthmatic phenotype, whereas the offspring from non-allergic parents do not. Offspring from ragweed-sensitized (two litters, n = 10) or non-sensitized (two litters, n = 11) Beagle dogs were exposed repeatedly, by inhalation, to ragweed or filtered air (negative control) beginning within 1 week after birth. Serum levels of total immunoglobulin (Ig)E, and ragweed-specific IgE and IgG, were measured at specific time-points up to 40 weeks after birth. Cell differentials in the bronchoalveolar lavage were determined on days 1 and 4 following ragweed instillation into the offspring's lungs at 26 weeks of age. Changes in pulmonary resistance following challenge with histamine and ragweed (five breaths) were measured at 40 weeks after birth. Offspring from sensitized parents exposed to ragweed developed elevated serum total IgE and ragweed-specific IgE and IgG, and showed an increased pulmonary resistance to histamine and ragweed, and increased numbers of eosinophils in bronchoalveolar lavage. In contrast, offspring from non-sensitized parents did not exhibit this immune response. These results suggest that parental allergic sensitivity is important in the development of allergic sensitization and an asthmatic phenotype in the offspring.

Relationships of allergic sensitization, total immunoglobulin E and blood eosinophils to asthma severity in children of the EGEA Study

BACKGROUND

Although allergy is highly associated with childhood asthma, it is not well known if there is a relationship between the intensity of allergic sensitization and asthma severity.

OBJECTIVE

The objectives of the study were to examine the relationships between several markers of allergy and asthma severity in asthmatic children included in the Epidemiological study on the Genetics and Environment of Asthma, bronchial hyper-responsiveness and atopy (EGEA).

METHODS

The population comprised 216 asthmatic children below 16 years of age. Total IgE and blood eosinophil counts were measured and skin prick tests to 11 aeroallergens were performed. The intensity of the allergic sensitization was assessed by the number of positive skin prick tests and by skin weal sizes. Asthma severity was measured with four criteria: a clinical severity score, history of hospitalization for asthma, FEV1% predicted and inhaled steroid use in the last 12 months.

RESULTS

Most of the children were sensitized to at least one aeroallergen (88.2%). Atopy was not related to the severity of asthma, except for a tendency for a more severe clinical score in non-atopic children. The type and intensity of the allergic sensitization were not associated with any criteria of asthma severity. Total IgE was significantly increased in children treated with inhaled corticosteroids and in children ever hospitalized for asthma (P-values 0.009 and 0.04, respectively). Eosinophil counts were not related to asthma severity.

CONCLUSION

Our results suggest that severe childhood asthma may be related to a high level of total IgE but not to blood eosinophil counts. The lack of positive relationships between both atopy and the intensity of allergic sensitization with asthma severity supports the hypothesis of different risk factors being associated with asthma and with the severity of asthma.

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.

Environmental factors relevant to difficult asthma

Symptom persistence in difficult asthmatics may be related to their home environment. If sensitised asthmatics are to benefit from indoor allergen avoidance measures, these must be rigorous and drug adherence satisfactory. This is difficult for many families. The relationship between traffic pollution, asthma diagnosis and symptom severity is persuasive but requires objective validation. Overall, it seems that house dust mite control and tobacco smoke avoidance are important for asthmatics and advice about how to avoid these adverse factors must be given. Whether these measures are effective in difficult asthmatics and whether moving house makes any difference is unknown.

Effect of cat and dog ownership on sensitization and development of asthma among preteenage children

An inverse relationship has been proposed between exposure to high quantities of cat allergen at home and both asthma and cat allergy. First- and second-grade children from Luleå, Kiruna, and Piteå, Sweden participated in an asthma questionnaire study (n = 3,431) and incidence was evaluated over the next 3 years. Skin testing was performed on the children in Luleå and Kiruna (n = 2,149). The strongest risk factor for incident cases of asthma was Type 1 allergy (relative risk [RR], 4.9 [2.9-8.4]), followed by a family history of asthma (RR, 2.83 [1.8-4.5]). Living with a cat was inversely related both to having a positive skin test to cat (RR, 0.62 [0.47-0.83]) and incidence of physician-diagnosed asthma (RR, 0.49 [0.28-0.83]). This effect on incident asthma was most pronounced among the children with a family history of asthma (RR, 0.25 [0.08-0.80]). The evidence also suggests that many of the children exposed to cats at home can develop an immune response that does not include immunoglobulin E. Weaker protective trends were seen with dog ownership. The traditional thinking that not owning cats can provide protection against developing allergy and asthma among those with a family history of allergy needs to be re-evaluated. In a community where cat sensitization was strongly associated with asthma, owning a cat was protective against both prevalent and incident asthma.

Placebo-controlled trial of house dust mite-impermeable mattress covers: effect on symptoms in early childhood

We investigated the effect of house dust mite (HDM)-allergen avoidance on the development of respiratory symptoms, atopic dermatitis, and atopic sensitization by performing a double blind, placebo-controlled trial. In total, 1,282 allergic pregnant women were selected (416 received HDM allergen-impermeable mattress covers for the parents' and child's mattress in the third trimester of pregnancy [active], 394 received placebo covers, 472 received no intervention). Data on allergen exposure, clinical symptoms, and immunoglobulin E were collected prospectively. The prevalence of night cough without a cold in the second year of life was lower in the group with active covers compared with the group with placebo covers (adjusted odds ratio 0.65; 95% confidence interval 0.4-1.0). No effect of the intervention was seen on other respiratory symptoms, atopic dermatitis, and total and specific immunoglobulin E. It can be concluded that application of HDM-impermeable mattress covers on the child's and parents' beds reduced night cough, but not other respiratory symptoms, atopic dermatitis, and atopic sensitization in the first 2 years of life. Follow-up will determine the long-term effect of the intervention on the development of atopic disease.

Feather bedding and house dust mite sensitization and airway disease in childhood

Feather bedding has been inversely associated with child wheeze and also with house dust mite (HDM) allergen levels. We conducted a cross-sectional analysis of the childhood component of a birth cohort study. Our aim was to examine the relation between feather bedding and HDM sensitization and airway disease. A total of 498 children (84% of eligible) residing in Northern Tasmania in 1997 who were eligible for the Tasmanian Infant Health Survey at birth in 1988 or 1989 participated. Outcome measures included atopic sensitization to Dermatophagoides farinae or Dermatophagoides pteronyssinus allergens, spirometric lung function, and child respiratory symptoms using questions from the ISAAC study. HDM sensitization was strongly associated with frequent wheeze (more than 12 episodes of wheeze compared with no wheeze in the past year) (rate ratio [RR], 19.61; confidence interval [CI], 6.94-55.56) but only weakly associated with asthma ever (RR, 1.65; CI, 1.30-2.09). Feather quilt use was associated with reduced HDM sensitization (adjusted RR [ARR], 0.60; CI, 0.45-0.80) and also reduced frequent wheeze episodes over the past year (ARR, 0.24; CI, 0.07-0.86). The reduction in wheeze was more evident among HDM-sensitized children. These findings are consistent with the possible mechanisms for feather bedding of a reduction in initial HDM sensitization and an improvement in respiratory symptoms among HDM-sensitized children. However, prospective studies are required to fully exclude selection bias.

Which clinical subgroups within the spectrum of child asthma are attributable to atopy?

STUDY OBJECTIVES

The contribution of atopy to childhood asthma has been debated. We aimed to examine the relationship between atopy and asthma, taking into account differences in respiratory symptoms and disease severity.

DESIGN

A cross-sectional asthma survey involving the following: (1) a population sample of 758 (81% of eligible) school children aged 8 to 10 years from randomly selected schools in the Australian Capital Territory in 1999, and (2) a hospital-based sample of 78 (70% of eligible) children attending the hospital for asthma. Skin-prick test results to 10 common aeroallergens were available on 722 children and 77 children, respectively. Baseline spirometry was obtained on a subset of school children (n = 515, 78% of eligible).

RESULTS

The association between atopy and wheeze by wheeze frequency over the past year was as follows: no episodes (odds ratio [OR], 1.00 [reference]), 1 to 3 episodes (OR, 3.27; 95% confidence interval [CI], 2.15 to 4.97), 4 to 12 episodes (OR, 3.44; 95% CI, 1.75 to 6.75), and > 12 episodes (OR, 8.70; 95% CI, 3.07 to 24.55), with a higher population attributable fraction (PAF) for > 12 episodes (75%) than 1 to 3 episodes (49%). Atopy was moderately related to asthma ever (OR, 2.09; 95% CI, 1.52 to 2.85; PAF, 33%) but strongly related to 1999 hospital attendance for asthma (OR, 16.95; 95% CI, 6.76 to 42.48; PAF, 89%). Adjustment for child age, gas heater use, and maternal smoking near the child did not materially alter these findings.

CONCLUSIONS

The clinical features of frequent wheeze or hospital asthma attendance are largely attributable to atopy, but infrequent wheeze or a history of asthma ever are not. Atopic children are overrepresented in the severe range of the asthma spectrum.

Indoor pollution and its impact on respiratory health

LEARNING OBJECTIVES

This overview discusses the respiratory complications of indoor air pollution, emphasizing the most common pollutants that individuals are likely to encounter outside the workplace.

DATA SOURCES

Data were obtained from a review of the recent literature.

STUDY SELECTION

The expert opinion of the author was used to select and synthesize relevant data on this multifaceted subject.

RESULTS

There have been a number of studies documenting an association between exposure to indoor allergens and development of both sensitization and asthma in children. In addition to classic allergens, chemical indoor air pollution may also exert an adverse effect on both the upper and lower respiratory tract by a variety of nonimmunologic, irritative mechanisms.

CONCLUSIONS

Our understanding of the adverse effects of indoor air pollution on health and comfort has broadened in recent years. It has supplied a credible framework for developing and implementing a variety of control strategies.

Asthma in preschool children: prevalence and risk factors

BACKGROUND

The prevalence of asthma in children has increased in many countries over recent years. To plan effective interventions to reverse this trend we need a better understanding of the risk factors for asthma in early life. This study was undertaken to measure the prevalence of, and risk factors for, asthma in preschool children.

METHODS

Parents of children aged 3-5 years living in two cities (Lismore, n=383; Wagga Wagga, n=591) in New South Wales, Australia were surveyed by questionnaire to ascertain the presence of asthma and various proposed risk factors for asthma in their children. Recent asthma was defined as ever having been diagnosed with asthma and having cough or wheeze in the last 12 months and having used an asthma medication in the last 12 months. Atopy was measured by skin prick tests to six common allergens.

RESULTS

The prevalence of recent asthma was 22% in Lismore and 18% in Wagga Wagga. Factors which increased the risk of recent asthma were: atopy (odds ratio (OR) 2.35, 95% CI 1.49 to 3.72), having a parent with a history of asthma (OR 2.05, 95% CI 1.34 to 3.16), having had a serious respiratory infection in the first 2 years of life (OR 1.93, 95% CI 1.25 to 2.99), and a high dietary intake of polyunsaturated fats (OR 2.03, 95% CI 1.15 to 3.60). Breast feeding (OR 0.41, 95% CI 0.22 to 0.74) and having three or more older siblings (OR 0.16, 95% CI 0.04 to 0.71) decreased the risk of recent asthma.

CONCLUSIONS

Of the factors tested, those that have the greatest potential to be modified to reduce the risk of asthma are breast feeding and consumption of polyunsaturated fats.

Asthma in preschool children: prevalence and risk factors

BACKGROUND

The prevalence of asthma in children has increased in many countries over recent years. To plan effective interventions to reverse this trend we need a better understanding of the risk factors for asthma in early life. This study was undertaken to measure the prevalence of, and risk factors for, asthma in preschool children.

METHODS

Parents of children aged 3–5 years living in two cities (Lismore, n=383; Wagga Wagga, n=591) in New South Wales, Australia were surveyed by questionnaire to ascertain the presence of asthma and various proposed risk factors for asthma in their children. Recent asthma was defined as ever having been diagnosed with asthma andhaving cough or wheeze in the last 12 monthsand having used an asthma medication in the last 12 months. Atopy was measured by skin prick tests to six common allergens.

RESULTS

The prevalence of recent asthma was 22% in Lismore and 18% in Wagga Wagga. Factors which increased the risk of recent asthma were: atopy (odds ratio (OR) 2.35, 95% CI 1.49 to 3.72), having a parent with a history of asthma (OR 2.05, 95% CI 1.34 to 3.16), having had a serious respiratory infection in the first 2 years of life (OR 1.93, 95% CI 1.25 to 2.99), and a high dietary intake of polyunsaturated fats (OR 2.03, 95% CI 1.15 to 3.60). Breast feeding (OR 0.41, 95% CI 0.22 to 0.74) and having three or more older siblings (OR 0.16, 95% CI 0.04 to 0.71) decreased the risk of recent asthma.

CONCLUSIONS

Of the factors tested, those that have the greatest potential to be modified to reduce the risk of asthma are breast feeding and consumption of polyunsaturated fats.

The childhood asthma prevention study (CAPS): design and research protocol of a randomized trial for the primary prevention of asthma

The Childhood Asthma Prevention Study is a randomized controlled trial to measure whether the incidence of atopy and asthma can be reduced by house dust mite allergen reduction, a diet supplemented with omega-3 fatty acids, or a combination of both interventions. Six hundred and sixteen pregnant women whose unborn children were at high risk of developing asthma because of a family history were randomized prenatally. Study groups are as follows: Group A (placebo diet intervention, no house dust mite reduction), Group B (placebo diet intervention, active house dust mite reduction), Group C (active diet intervention, no house dust mite reduction), and Group D (active diet intervention, active house dust mite reduction). The house dust mite reduction intervention comprises use of physical and chemical methods to reduce allergen contact. The dietary intervention comprises use of a daily oil supplement from 6 months or at onset of bottle-feeding, and use of margarine and cooking oils based on sunflower or canola oils to increase omega-3 dietary intake. Data is collected quarterly until the infant is 1 year old and then half yearly until age 5 years. Questionnaires are used to collect respiratory illness history and information about diet and home environment. Dust is collected from the child's bed and bedroom and playroom floors. Blinded assessments are conducted at 18 months, 3 years, and 5 years. Skin prick tests to common allergens, blood tests, and detailed illness, medication use, and vaccination histories are collected. Primary outcomes will be the development of allergic sensitization and the presence and severity of asthma. This study is designed to measure the effectiveness of allergen reduction and dietary supplementation, both separately and in combination, for the primary prevention of atopy and asthma. The results of this study may have important implications for public health policies to reduce the incidence of childhood asthma. Control Clin Trials 2001;22:333-354

The importance of allergens in the development of asthma and the persistence of symptoms

The importance of allergies and allergens in the development and persistence of asthma is suggested by 3 lines of evidence. First, a number of epidemiologic studies demonstrate that sensitization to indoor allergens and the spores of the outdoor seasonal fungus Alternaria is a risk factor for the development of asthma in both children and adults. Sensitivity to pollens, on the other hand, rarely constitutes a risk for asthma but does constitute a risk for seasonal allergic rhinitis. Second, several studies, again in both children and adults, have demonstrated that, in persons sensitive to indoor allergens, the severity of asthma symptoms will vary with the level of exposure. Third, the elimination of exposure to house-dust mites has produced a remarkable reversal of asthma in sensitive children and adults. Not only have symptoms and pulmonary function improved, but there has also been evidence of a reduction in airway inflammation and hyperresponsiveness. Taken together, these studies make a strong argument for the importance of allergy and allergen exposure as aggravating factors in asthma in both children and adults and reinforce the importance of the identification and treatment of these allergen sensitivities. (J Allergy Clin Immunol 2000;105:S628-32.)

Polymorphisms in the IL4, IL4RA, and FCERIB genes and asthma severity

BACKGROUND

Genetic polymorphisms have been associated with asthma and asthma severity.

OBJECTIVE

We sought to determine whether 3 polymorphisms were associated with severe asthma indicated either by the occurrence of a fatal (or near-fatal) asthma attack or by severe airflow obstruction.

METHODS

We obtained DNA and clinical data from asthmatic subjects who either died or nearly died during an asthma attack and from a group of subjects with mild-to-moderate asthma who had never experienced a fatal or near-fatal asthma episode. These groups were compared with a group of nonatopic nonasthmatic control subjects. The level of airflow obstruction (FEV(1) percent predicted) in the subjects with mild-to-moderate asthma was used as an additional measure of disease severity. The subjects were genotyped for the IL4*C-589T promoter polymorphism and the IL4RA*Q576R and the FCERIB*E237G amino acid substitutions.

RESULTS

The results showed that the FCERIB*E237G and IL4RA*Q576R polymorphisms were not associated with fatal or near-fatal asthma. However, the IL4*-589T allele was significantly increased in the subjects with fatal or near-fatal asthma compared with nonasthmatic subjects (odds ratio [OR], 1.8; P =.02) and subjects with mild-to-moderate asthma (OR, 1.9; P =.02). There was no interaction between the IL4*-589T and IL4RA*576R alleles. Of the 3 polymorphisms, only the IL4RA*576R allele was associated with severe airflow obstruction (OR, 8.2; P =.01).

CONCLUSION

These data suggest that the IL4*-589T allele is a risk factor for life-threatening asthma and that the IL4RA*576R allele is a risk factor for a low level of lung function in asthmatic subjects.

Domestic control of house dust mite allergen in children's beds

BACKGROUND

House dust mite allergen levels in humid coastal regions of Australia are high, particularly in beds. Because high allergen levels in beds are associated with more severe asthma, reduction of levels may be important for asthma control.

OBJECTIVE

We tested the effectiveness of an acaricidal treatment of bedding in combination with occlusive mattress and pillow encasings in reducing allergen levels in children's beds in a community setting.

METHODS

A total of 14 beds of children were selected for the active intervention. In each home the bed of a sibling of nearest age was selected as the control. Dust was vacuumed from beds by using a standard protocol, and Der p 1 levels were measured by using ELISA. Adjacent settling dust was collected by using opened Petri dishes. The intervention consisted of encasing mattresses and pillows in occlusive covers and washing all bedding with Acaril, an acaricidal additive. The acaricidal wash was repeated twice in 7 households at 2-month intervals. Control beds were not treated.

RESULTS

The mean Der p 1 concentration at baseline was 27.9 microg/g in the active beds and 18.1 microg/g in the control beds. At 4 days after intervention, Der p 1 decreased to 3.2 microg/g and 15.7 microg/g in active and control beds, respectively. The average difference (active minus control) over the first 8-week cycle was 78.5% (P <.0001), and the difference over 3 washing cycles was 125.1% (P <.05). The mean rate of settling Der p 1 adjacent to the actively treated beds decreased from 24.4 ng.m(-2).d(-1) at baseline to 10.0 ng.m(-2).d(-1) after intervention (P <.01).

CONCLUSION

A substantial reduction in Der p 1 levels in beds and in airborne dust in a humid region with naturally high house dust mite allergen levels can be achieved and sustained in a community setting with use of occlusive covers and a rigorous washing routine.

The importance of allergens in the development of asthma and the persistence of symptoms

The importance of allergies and allergens in the development and persistence of asthma is suggested by 3 lines of evidence. First, a number of epidemiologic studies demonstrate that sensitization to indoor allergens and the spores of the outdoor seasonal fungus Alternaria is a risk factor for the development of asthma in both children and adults. Sensitivity to pollens, on the other hand, rarely constitutes a risk for asthma but does constitute a risk for seasonal allergic rhinitis. Second, several studies, again in both children and adults, have demonstrated that, in persons sensitive to indoor allergens, the severity of asthma symptoms will vary with the level of exposure. Third, the elimination of exposure to house-dust mites has produced a remarkable reversal of asthma in sensitive children and adults. Not only have symptoms and pulmonary function improved, but there has also been evidence of a reduction in airway inflammation and hyperresponsiveness. Taken together, these studies make a strong argument for the importance of allergy and allergen exposure as aggravating factors in asthma in both children and adults and reinforce the importance of the identification and treatment of these allergen sensitivities.

Increased nitric oxide production in the respiratory tract in asymptomatic pacific islanders: an association with skin prick reactivity to house dust mite

BACKGROUND

Exhaled nitric oxide (NO) is increased in asthma and may also be increased in subclinical airway inflammation. The relationship between atopy and subclinical airway inflammation in the pathogenesis of asthma remains unclear. We have evaluated the relationship between exhaled NO levels and skin prick test reactivity to 8 common allergens in 64 asymptomatic adult Pacific Islanders. Pacific Islanders were studied as a racial group with major morbidity from asthma.

OBJECTIVE

Our purpose was to determine whether asymptomatic subjects with skin prick test reactivity to common allergens have elevated NO levels.

METHODS

All subjects underwent full lung function testing and skin prick testing. Exhaled and nasal NO levels were measured by chemiluminescence (Logan LR2000 analyzer) with use of the single-breath and breath-holding techniques, respectively.

RESULTS

House dust mite (HDM) reactivity was seen in 38 of 64 (56%). Exhaled NO levels (median 8.9 ppb, range 2.9-47.3 ppb) and nasal NO levels (527.5 +/- 181.5 ppb) lay above the normal European range in 30% and 25% of subjects, respectively. HDM reactivity was associated with higher exhaled NO levels (P <. 0005) and higher nasal NO levels (P =.01). In HDM-sensitive subjects the wheal size for HDM correlated with exhaled NO levels (r = 0.35, P =.04) and nasal NO levels (r = 0.40, P =.01). On multivariate analysis, exhaled NO levels were independently and positively related to the severity of HDM reactivity (P =.01) and nasal NO levels (P <.02), equation R(2) = 0.27.

CONCLUSION

NO levels are elevated in a significant proportion of asymptomatic Pacific Islanders and are associated with HDM sensitivity. This may denote subclinical airway inflammation in this population and suggests that exposure to HDM in atopic individuals might play an important role in the early pathogenesis of asthma.

Asthma and the home environment

Recent years have seen a global increase in asthma prevalence. This has coincided with modifications to the home environment resulting in changes to the indoor air quality. This article considers the links between indoor pollution and asthma. Exposure to a range of substances is examined. Airborne allergens such as those from house dust mites may be important. Pollution from particulate materials associated with combustion and smoking is discussed, as is the role of chemical vapors and gases including nitrogen dioxide, sulfur dioxide, and volatile organic compounds. The efficacy of various environmental controls to limit the impact of these pollutants is explored.

The relevance of allergen exposure to the development of asthma in childhood

Sensitization to 1 or more of the common indoor allergens has been consistently associated with asthma among children and young adults (odds ratios for asthma, 3-18). For dust mite and cockroach allergens, there is a dose response relationship between domestic exposure and sensitization. Given that allergen provocation can induce many of the features of asthma, the findings strongly suggest that there is a causal relationship between allergen exposure in the home and asthma. However, it remains unclear at what time the critical exposure occurs (ie, in infancy or later) and what role allergen exposure has played in the increasing prevalence and severity of asthma. Objective evidence of an immune response to allergens is generally not present until after 2 years of age. Viral infections play several different roles in asthma in childhood. In infancy, respiratory syncytial virus infection can induce bronchiolitis and set up recurrent wheezing over the next few years. However, the risk factors for this are maternal smoking and small lungs at birth, rather than allergy. By contrast, the role of rhinovirus in precipitating attacks in children and young adults is strongly associated with allergy. Thus the likely scenario is that allergen exposure over the first few years of life induces sensitization (ie, T(H2) cells and IgE antibodies). Continuing exposure can maintain inflammation in the nose and lungs. However, many other factors contribute to wheezing such that there is no simple relationship between allergen exposure and asthma. Nonetheless, it is clear that the changes that have increased asthma have acted on allergic children.

Exhaled nitric oxide, sensitization, and exposure to allergens in patients with asthma who are not taking inhaled steroids

The level of exhaled nitric oxide (eNO) is elevated in patients with asthma and eNO may be involved in airway inflammation. Exposure to allergen in sensitized individuals may contribute to airway inflammation. Our aim was to investigate the relationship between eNO, sensitization, and exposure to indoor allergen in nonsmoking adults with asthma who are not taking inhaled steroids. In subjects with a positive methacholine challenge (PD20 < 4 mg) we measured eNO (LR 2000 chemiluminesence analyzer); serum total and specific IgE; skin test to mite, cat, and dog; and allergen levels in domestic dust (Der p 1, Fel d 1, and Can f 1). Subjects were classified as exposed or not exposed to allergen according to previously proposed significant levels (> 2 micrograms/g Der p 1, > 8 micrograms/g Fel d 1, and > 10 micrograms/g Can f 1). Of the 43 subjects (> 95% atopic) complete data were available for 38, of whom 26 were both sensitized and exposed to one or more allergen and 12 were sensitized but not exposed to any allergens. eNO was significantly higher in those subjects who were both sensitized and exposed to indoor allergen than in those who were sensitized but not exposed (GM and 95% CI: 17. 69 [14.1- 22.15] versus 9.09 [6.5-12.7], p = 0.001). Levels of eNO are significantly higher in patients with asthma who are both sensitized and exposed to relevant allergen than in those who were sensitized but not exposed. eNO may be a marker of the airway inflammation induced by domestic exposure to allergen in sensitized patients with asthma.

Importance of indoor allergens in the induction of allergy and elicitation of allergic disease

During the last few decades, many countries have experienced an increase in the prevalence and severity of asthma. Over the same period, the population in the developed world has retreated indoors, and homes have become better insulated and more energy efficient, resulting in a warm and humid environment with low ventilation rates, ideally suited to house-dust-mite population growth throughout the year. Increasing exposure and increasing sensitivity to indoor allergens represent a progressively higher risk factor for the development of asthma. The development of sensitivity to indoor allergens and the symptoms and severity of asthma in later childhood are directly related to the exposure to allergens in infancy. It was relatively straightforward to demonstrate a quantitative linear dose-response relationship between exposure to house-dust-mite allergens and subsequent sensitization. However, showing the same for exposure and asthma severity has been more difficult, as the relationship between exposure and asthma symptoms in already sensitized individuals is much more complex than in the case of exposure and sensitization. Nevertheless, sensitized individuals are likely to have more severe asthma if exposed to high allergen levels than if their level of exposure is low. Sensitization to house-dust mites is a major independent risk factor for asthma in all areas where climate is conducive to mite population growth. The relevance of allergens other that mite is not consistent between different areas, and depends on the climate, habits, and socio-economic features of the local community. It would appear that presence of mite allergens in homes "overshadows" other allergens (e.g., cat, dog, or cockroach) as a risk factor for sensitization and subsequent development of allergic disease. It is possible that this is the consequence of the difference in inherent potency between allergen sources, and the question of why mite allergens are so potent in inducing sensitization and atopic disease remains to be answered.

Methods and effectiveness of environmental control

In recent years the role of allergen exposure and atopy, and the interaction between them in the clinical expression of allergic disease, has been examined in a quantitative manner in epidemiologic studies. Such analyses suggest that avoidance of exposure to domestic allergens is a critical element in integrated strategies for both the prevention and the management of asthma. The promise of primary intervention in high-risk infants, as shown in the Isle of White study, has been confirmed in a recent study in Japan, and at least 4 similar trials are in progress. Applying these principles to the management of symptoms in patients with chronic asthma has proved more difficult, and it is likely that many earlier studies were poorly designed to test the hypothesis that allergen avoidance was clinically useful. Recent studies with patients moved to high altitudes during seasonal reductions in mite exposure and randomized controlled interventions in houses have all shown improvements in clinical manifestations of asthma. These recent trials have also demonstrated something that was less certain-that massive reductions in domestic allergen exposure can be achieved and that people will adopt the significant changes to their domestic environment and lifestyles if the risks and benefits are known. In the future, it seems likely that better study designs, as well as improvements in methods to monitor exposure and clinical outcomes, will provide further support for the role of allergen avoidance in the prevention and management of asthma.

Environmental allergens and childhood asthma

Exposure to allergens has been shown to lead to sensitization and to the subsequent development of airway hyperresponsiveness in genetically predisposed individuals. Increasing interest is being devoted to mechanisms for the prevention of allergen sensitization and asthma development. Primary prevention (avoiding the sensitization to allergens) requires a large effort as the majority of atopic sensitizations occur in children with no demonstrable risk at the birth. Secondary prevention (deterrence of disease expression despite prior IgE sensitization) requires methods for detecting the population at risk by means of large population screening. Tertiary prevention (minimizing the morbidity for those who already have the disease) may be achieved by allergen avoidance, which has been demonstrated to effectively decrease inflammation in symptomatic patients.

The role of IgE in asthma

Asthma is a multifactorial and complex disease in which allergic factors and non-allergic triggers interact and result in bronchial obstruction and inflammation. Allergenic sensitization is important in the development of asthma and, although links between inhalant allergy and asthma have been known for many years, they have recently been re-emphasized. Indoor allergens are associated with asthma prevalence, severity and exacerbations whereas outdoor allergens such as pollens are associated with exacerbations. Moreover, there is a link between total IgE and asthma which appears to be independent of allergen sensitization. One of the typical aspects of airway inflammation of asthma is the infiltration of the airway wall by T helper type 2 (Th2) cells. These cells are attracted to inflammatory sites by adhesion molecules and chemokines among which CCR3 and CXCR4 receptors appear to be of importance. Differentiation of B cells into IgE-secreting plasma cells is a complex cascade of events in which cytokines play a crucial role. Both IL-4 and IL-13 are inducing IgE synthesis whereas IFN-gamma and IL-12 are blocking IgE synthesis. IgE production by B cells not only requires the presence of IL-4 or IL-13, but also a physical interaction between T and B cells, involving a number of surface and adhesion molecules such as CD40-CD40L and CD28/CD80. Production of TH2-cytokines is not restricted to T cells as basophils and mast cells can produce them indicating that these cells may be of importance in the synthesis of IgE.

Association between Der p 1 concentration and peak expiratory flow rate in children with wheeze: a longitudinal analysis

BACKGROUND

House dust mite (HDM) allergen exposure has been well documented as an environmental cause of airway hyperresponsiveness (AHR) and asthma symptoms. The relationship between asthma morbidity and exposure to low concentrations of HDM allergen suggests that there may be no safe exposure threshold to HDM allergen.

OBJECTIVE

We aimed to investigate the associations between Der p 1 in bedding and lung function in 30 children with a history of wheezing in a longitudinal study.

METHODS

After a cross-sectional study of school children, which included histamine challenge for AHR and skin testing for dust mite atopy, we made repeated measurements of HDM allergens in children with a history of wheeze over a 12-month period. These children also kept a daily asthma diary in which they recorded their peak expiratory flow rates (PEFRs). We used a repeated measures model to determine the association between PEFR and HDM allergen concentration.

RESULTS

There was a significant association between PEFRs and HDM allergen concentration (beta-coefficient = -14.17, P = .0024) in children with HDM atopy. An association was not found in children without HDM atopy.

CONCLUSIONS

These findings support the hypothesis that HDM allergens have an adverse effect on the lung function of children with wheeze and highlight the importance of maintaining low dust mite allergen levels throughout the year in the home environment of children sensitized to HDMs.

Asthma and domestic air quality

In recent years, there has been a global increase in the prevalence of asthma. This has coincided with many modifications to the home environment, resulting in changes to the quality of indoor air. This article considers the links between indoor air pollution and asthma. Exposure to a range of pollutants is examined. Airborne allergens such as those from house dust mites and cockroaches, domestic pets and moulds and fungal spores may be important. Pollution from particulate materials associated with bio-fuel combustion and smoking is discussed, as is the role of chemical vapours and gases including nitrogen dioxide, formaldehyde and volatile organic compounds. The efficacy of various environmental controls to limit the impact of these pollutants is explored. It is concluded that indoor air pollution may be an important risk for asthma and the health impacts of building design and management require greater recognition and further research.

Role of the indoor environment in determining the severity of asthma

Allergen exposure can confound the management of asthma. To understand the potential mechanisms by which allergens increase the steroid requirements in atopic asthmatics, we examined the effects of allergens on glucocorticoid receptor (GCR) binding affinity and glucocorticoid (GC) responsiveness of peripheral blood mononuclear cells (PBMC) from atopic asthmatics. A significant reduction (p < 0.001) in the GCR binding affinity (Kd) was observed in ragweed-allergic asthmatics during ragweed pollen season compared with PBMC obtained before and after ragweed season. In vitro effects of allergen on PBMC GCR Kd were also examined by incubating PBMC from atopic asthmatics with allergen (ragweed and cat) versus Candida albicans. GCR binding affinity was significantly reduced after incubation with ragweed (p < 0.001) or cat allergen (p < 0.001) compared with baseline or C. albicans stimulation. This effect was limited to atopic asthmatics in that in vitro cat allergen incubation for 48 h failed to significantly alter GCR binding affinity in nonasthmatic, atopic individuals. These allergen-induced reductions in GCR binding affinity also rendered the PBMC less sensitive to the inhibitory effects of hydrocortisone and dexamethasone on allergen-induced proliferation (p < 0.01). To test the hypothesis that allergen-induced alterations in GCR binding affinity were cytokine-induced, we examined the effects of interleukin-2 (IL-2) and IL-4 neutralization using anticytokine antibodies. Addition of both anti-IL-2 and anti-IL-4 antibodies resulted in a significant (p < 0.001) inhibition of allergen-induced alterations in GCR binding affinity. Furthermore incubation with cat allergen induced significantly higher concentrations of IL-2 (p = 0.03) and IL-4 (p = 0.02) by PBMC from atopic as compared with nonatopic subjects. Our current observations suggest that allergen exposure may contribute to poor asthma control by reducing GCR binding affinity in mononuclear cells. This appears to be mediated through IL-2 and IL-4. These findings may have important implications for novel approaches to the treatment of poorly controlled asthma.

Individual allergens as risk factors for bronchial responsiveness in young adults

BACKGROUND

Bronchial responsiveness is known to be related to atopy, but the relative contribution of sensitisation to individual allergens in the UK, or whether serum total IgE is an independent risk factor, is unknown.

METHODS

A random sample of 1864 men and women aged 20-44 years, drawn from family health service registers in Cambridge, Ipswich and Norwich, was invited to answer a detailed questionnaire, undergo skin prick tests and methacholine bronchial challenge, and provide a serum sample for measurement of total and specific IgE. The relation of bronchial responsiveness to risk factors was studied in 749 subjects (40.2%) with complete data.

RESULTS

Bronchial responsiveness was increased in those sensitised to cat, D pteronyssinus, Timothy grass and Cladosporium, but decreased in subjects also positive to birch allergen. Additional skin prick tests added little information. Serum total IgE was not significantly related after adjustment for specific IgE to the five allergens. Increasing titres of specific IgE to D pteronyssinus were associated with increasing bronchial responsiveness. Specific IgE to Cladosporium had a prevalence of around 3%, but was associated with greatly increased responsiveness. Decreased baseline lung function was related (p < 0.001) to increased responsiveness. There was an interaction between age and smoking status, with lower responsiveness in older non-smokers.

CONCLUSION

Atopy is the most important risk factor for bronchial responsiveness in this age group, but effects are not additive across all allergens. Research in reducing exposure to house dust mite should also address the role of Cladosporium sensitisation and exposure to indoor moulds.