Effect of environmental manipulation in pregnancy and early life on respiratory symptoms and atopy during first year of life: a randomised trial

Food allergy: what can be done to prevent progression to asthma?

OBJECTIVES

The primary objective of this review is to discuss risk factors for asthma development in food allergen-sensitized children. In the paper we discuss the possible measures to prevent progression to asthma by allergen and other adjuvant factor avoidance.

DATA SOURCES

A review from literature of articles on these topics was performed.

STUDY SELECTION

Relevant publications on asthma risk factors and implementation of protective factors were critically evaluated.

RESULTS

Children with familiar history of atopy and sensitization to food proteins in early infancy are at high risk of subsequent respiratory allergic diseases and require specific prevention. Because early allergic sensitization is a significant risk factor for later development of asthma, prevention of asthma by early allergen avoidance is mandatory in high-risk children. Adjuvant factors such as tobacco smoke and mold exposure may act as nonspecific triggers for the development of atopy. The role of protective factors such as infections in early life, breast-feeding, a "healthy" diet needs to be evaluated in prospective studies. Pharmacologic intervention with antihistamines led to significant reduction in incidence of asthma in high-risk children, but confirmatory longitudinal studies in large populations are necessary.

CONCLUSIONS

There is now accumulating evidence that preventing exposure to house-dust mite may significantly reduce the prevalence of childhood asthma. However, allergen avoidance can not be recommended as the only strategy. Avoidance of adjuvant factors and implementation of potential protective factors aimed to reduce the risk to progression to asthma need to be evaluated in prospective studies.

Clostridium difficile, atopy and wheeze during the first year of life

Differences have been suggested to occur in the composition of intestinal microflora from allergic and non-allergic children. In this study we used a semi-quantitative enzyme-linked immunosorbent assay (ELISA) for the measurement of Clostridium difficile-specific immunoglobulin G (IgG) (CDIgG). CDIgG was excellent in differentiating between adults with or without Cl. difficile colitis (absorbance levels, positive vs. negative controls: geometric mean (GM) 0.301, 95% CI: 0.289-0.314 vs. GM 0.167, 95% CI: 0.155-0.181; mean difference 1.8-fold, 95% CI: 1.65-1.95; p < 0.0001). We used this technique to investigate whether there are any differences between atopic wheezy infants and non-atopic non-wheezy controls. In a prospective cohort study (n = 390) 10 patients were identified at 1 year of age (atopic, history of recurrent wheeze) and matched (gender, month of birth, exposure to Der p 1, Fel d 1 and Can f 1) with a control group of infants (non-atopic, no history of wheeze). The patients had significantly higher Cl. difficile-specific IgG absorbance levels (GM 0.298, 95% CI: 0.249-0.358) compared with controls (GM 0.235, 95% CI: 0.201-0.274; mean difference 1.27-fold, 95% CI: 1.07-1.50; p = 0.01). These results suggest that there may be differences in the composition of intestinal microflora between allergic and non-allergic infants at 1 year of age, with allergic children having higher Cl. difficile IgG antibody levels.

Daycare centers and schools as sources of exposure to mites, cockroach, and endotoxin in the city of São Paulo, Brazil

BACKGROUND

Public places, including schools, have been identified as sources of exposure to allergens derived from mites, cockroach, cat, and dog and to endotoxin.

OBJECTIVES

The purposes of this study were to assess and compare exposure to allergens and endotoxin in 4 types of public child-care facilities in Brazil and to investigate whether the presence of children and the performance of cleaning procedures could have an influence on allergen and endotoxin levels.

METHODS

We have analyzed dust from bedding, floors, chairs, and tables of daycare centers (DCs), preschools, kindergartens, and elementary schools (ESs). Major allergens from mites, cockroach, cat, and dog were quantitated by means of ELISA, and endotoxin content was determined by using the Limulus Amebocyte Lysate assay.

RESULTS

Group 1 mite allergens were greater than 2 microg/g in 67% of DC and preschool samples and in 8.9% and 2.2% of kindergarten and ES samples, respectively. The presence of bedding in DCs and preschools accounted for increased levels of mite allergens in these settings. Levels of Bla g 1 were higher in ES floors compared with those found in DC and preschool floors. Low levels (<1 microg/g) of Fel d 1 e Can f 1 were found in most samples. Levels of endotoxin in DCs and preschools were 3 times higher than in ESs.

CONCLUSIONS

DCs and schools in Brazil should be considered as important sources of exposure to dust mites and cockroach allergens and to endotoxin. Recommendations for mite allergen avoidance should include appropriate care of bedding in DCs and preschools.

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?

Is prevention of childhood asthma possible? Allergens, infections and animals

What we know: Epidemiological studies have identified a number of factors associated with increased incidence of asthma. These include allergen sensitisation and exposure, reduced exposure to infections and to farm animals in early childhood, and maternal smoking. These factors may represent "true" risk factors for asthma or may be merely associated factors that do not in themselves cause asthma. The "hygiene hypothesis" has been proposed as one mechanism by which infections may protect against asthma. Current recommendations for the primary prevention of asthma include exclusive breastfeeding for the first six months of life, avoidance of maternal smoking during pregnancy and infancy, and reducing the levels of house-dust mite in some environments. What we need to know: What are the mechanisms by which specific risk factors and prevention strategies lead to or protect from asthma? How do genetic and environmental factors interact to increase the risk of asthma?

Preventive measures and their effects. Results from cohort studies

The prevalence of asthma and atopic diseases continues to rise. Genetic factors alone cannot explain this rapid rise and the immunological mechanisms involved are insufficiently explained to allow direct intervention on a population-wide scale. Long-term observational birth cohort studies have provided data on which primary prevention studies are based. This review discusses the "who", "how", "when" and "what" of primary prevention and the experiences to date in prospective intervention cohort studies.

Environmental controls in the management of allergic asthma

Environmental allergen control is one of the four primary goals of good asthma management. The American Academy of Allergy, Asthma, and Immunology has published a position statement [78] that endorses the National Asthma Education and Prevention Program management guidelines [23] and recommends that every patient with persistent asthma be evaluated for environmental allergen sensitivity. Patients who have sensitivities should receive practical advice on allergen avoidance. An accumulating body of knowledge indicates that such measures, when strictly applied for a sufficient period of time, can indeed reduce asthma symptoms, need for medication, and airway hyperresponsiveness. Ongoing prospective trials in large numbers of patients are being conducted and should enhance the ability to make proper recommendations to patients.

The effect of allergen exposure in early childhood on the development of atopy

While there is good evidence for the association between allergen exposure and disease severity in sensitized individuals, and allergen exposure and development of sensitization, the relationship between allergen exposure and development of allergic disease is as yet unresolved. A protective effect of cat ownership on sensitization and allergic disease has been reported. The dose-response relationship between allergen exposure and sensitization may be different for different allergens (eg, linear for mite, bell-shaped for cat). Exposure to a high level of cat allergen may result in a modified Th2 response characterized by the presence of IgG4 antibody to cat proteins without IgE response, which could be regarded as a form of tolerance. The long-term prospective follow-up of well-defined cohorts with objective exposure and outcome measures will elucidate the complex relationship between environmental allergen exposures, sensitization, and 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.

Early predictors of asthma

A number of recent cohort and cross-sectional studies have contributed substantial knowledge to factors that influence the early development of asthma. Here, we summarize the recent evidence for the role of early life events such as prenatal factors, infections, diet and allergen exposure, and discuss the implications for future preventative strategies.

Specific airway resistance in 3-year-old children: a prospective cohort study

BACKGROUND

The development of a method to assess lung function in young children may provide new insight into asthma development. Plethysmographic measurement of specific airway resistance (sR(aw)) is feasible in this age group. We aimed to identify risk factors associated with low lung function in early childhood in a prospective birth cohort.

METHODS

Children were prenatally assigned to risk group according to parental atopic status (high risk, both parents atopic; medium risk, one parent atopic; low risk, neither parent atopic) and followed prospectively until age 3 years. We measured sR(aw) in 503 symptom-free children using whole-body plethysmography during tidal breathing.

FINDINGS

803 of 868 children attended the clinic, of whom 503 obtained satisfactory sR(aw) readings. 200 who wheezed at least once during first 3 years of life had significantly higher sR(aw) than the 303 who had never wheezed (mean difference 5.8%, 95% CI 2.2-9.3, p=0.002). For children who had never wheezed there were significant differences in sR(aw) between risk groups (p<0.001). Children at high risk (n=87) had a higher sR(aw) (geometric mean 1.17 kPa/s, 1.12-1.22) than children at medium risk (n=162; 1.02 kPa/s, 1.00-1.05) and at low risk (54; 1.04 kPa/s, 0.99-1.11). Atopic children (n=62) had significantly higher sR(aw) (1.15 kPa/s, 1.09-1.21) than those who were not atopic (232; 1.05 kPa/s, 1.02-1.07, p=0.002). For non-atopic children, those at high risk (58) had higher sR(aw) (1.13kPa/s, 1.07-1.18) than those at medium risk (125, 1.01kPa/s, 0.98-1.05) or at low risk (49, 1.04 kPa/s, 0.97-1.10, p=0.003). We showed a significant interaction between history of maternal asthma and child's atopic status (p=0.006).

INTERPRETATION

Even in the absence of respiratory symptoms, children of atopic parents and those with personal atopy have impaired lung function in early life.

Controlling indoor allergens

OBJECTIVES

Reading of this article reinforces the reader's knowledge of the role of allergen exposure in relation to asthma and its severity, as well as the relevance of allergen avoidance in the treatment of asthma.

DATA SOURCES

Initial literature search for existing evidence-based guidelines, reviews, and meta-analyses was carried out, and further literature searches were performed to review individual randomized controlled trials. Evidence level was graded according to the Scottish Intercollegiate Guidelines Network recommendations.

RESULTS

There is good evidence for the link between mite and cockroach allergen exposure and sensitization, and between sensitization and asthma. For pet allergens, some studies found that exposure to pets in early life was associated with specific immunoglobulin E sensitization and allergic disease later in childhood, whereas others reported a protective effect. The effectiveness of allergen reduction in the treatment of asthma is suggested by studies in which the patients improve substantially when moved into the low-allergen environment of hospitals or high-altitude sanatoria. Because of limitations in the design of the most clinical of studies, we do not yet have a conclusive answer on the effectiveness of domestic aeroallergen avoidance.

CONCLUSIONS

Minimizing the impact of identified environmental risk factors is an important first step to reduce the severity of asthma. Although environmental control is difficult, it should be an integral part of the overall management of sensitized patients. However, what is unclear is which patients would benefit and by how much, and whether the intervention is cost-effective. These questions will be answered satisfactorily only by large randomized trials.

Lung function at one month of age as a risk factor for infant respiratory symptoms in a high risk population

BACKGROUND

Abnormal premorbid lung function is a risk factor for subsequent wheezing in children with one or no atopic parent. This study was undertaken to establish whether early lung function in high risk infants (both parents atopic) was a risk factor for respiratory symptoms in infancy and to examine the influence of maternal asthma, smoking, and allergen exposure during pregnancy on any association.

METHODS

Infants were recruited from the NAC Manchester Asthma and Allergy Study cohort at birth. Partial forced expiratory flow volume technique under sedation was carried out to determine maximal flow at FRC (V'maxFRC). Children were followed prospectively and parents completed a standard respiratory questionnaire at one year of age.

RESULTS

Sixty nine term infants (34 boys; 88% mothers non-smokers; no household pets) underwent respiratory function testing. Size adjusted V'maxFRC was significantly lower in infants who had recurrent wheeze during the first year of life (mean 1.3 ml/s/cm, 95% CI 0.99 to 1.60) than in those who did not (mean 2.03 ml/s/cm, 95% CI 1.71 to 2.36; p=0.01). V'maxFRC was also significantly lower in infants who had recurrent cough symptoms. In multivariate regression analysis, when adjusted for age at test, sex, maternal asthma, smoking and maternal mattress Der 1 levels, a lower size adjusted V'maxFRC score remained strongly associated with wheezing (OR 0.37, 95% CI 0.18 to 0.77, p=0.007). Maternal smoking also remained an independent risk factor (OR 29.85, 95% CI 2.46 to 362.5, p=0.008).

CONCLUSION

Significantly diminished lung function was present in high risk infants who subsequently wheezed and coughed. This was independent of maternal exposure to mite allergen, asthma, and smoking during pregnancy.

The National Asthma Campaign Manchester Asthma and Allergy Study

The NACManchester Asthma and Allergy Study is a prospective study of the development of asthma and allergies in childhood. The subjects (995 children at age 3 years) were recruited in utero by screening parents in the antenatal clinic using skin prick testing and a questionnaire regarding allergic diseases. Children were assigned to risk groups according to parental atopic status (high risk, both parents atopic; medium risk, one parent atopic; low risk, neither parent atopic). A subgroup of those at high risk (with no pets in the home) was randomized to stringent environmental control (allergen impermeable covers for the parental and infant bed, hot washing of bedding weekly, HEPA vacuum cleaner, hard floor for the nursery), and the remainder followed a normal regime. The children have been followed prospectively. The environmental influences are very clearly defined. Measurements of environmental exposures include levels of house dust mite; cat and dog allergens during pregnancy and early life; pet ownership and exposure; childcare arrangements; number of siblings; vaccination uptake; thorough dietary questionnaire; and endotoxin exposure. Further unique objective outcome in the cohort is the assessment of lung function in preschool children using specific airways resistance, which at age 3 years clearly reflects both genetic and environmental influences.

What's new in respiratory allergy?

The past 10 years have seen important advances in our understanding of allergic respiratory disease and the targets for potential therapies. Sensitisation and triggering of allergic reactions now appear to be better understood at a clinical and molecular level. Environmental intervention studies are underway attempting to reduce the sensitisation and the triggering of symptoms. Therapeutic intervention studies targeting key pathways in the allergic cascade are also taking place. This paper will assess both of these aspects of respiratory allergy, updating readers on the new evidence in our quest to understand how and when sensitisation occurs and also how we might be able to control triggered reactions using targeted therapeutics against specific elements of the allergic cascade.