The 8-year follow-up of the PIAMA intervention study assessing the effect of mite-impermeable mattress covers

BACKGROUND

Exposure to high levels of house dust mite (HDM) allergens is associated with the development of allergic sensitization to HDM, a risk factor for the development of asthma, rhinitis, and allergic dermatitis. We studied the effect of an early intervention with mite-impermeable mattress covers on HDM allergen levels and the development of asthma and mite allergy throughout the first 8 years of life.

METHODS

High-risk children (allergic mother) were prenatally recruited and randomly allocated to two groups receiving mite allergen-impermeable (n = 416) and placebo mattress covers (n = 394) or no intervention (n = 472). Asthma and allergies were assessed yearly by questionnaire. Specific immunoglobulin E and bronchial hyper-responsiveness were measured at the age of 8 years. Mattress dust samples collected at different time points were analyzed for HDM allergens.

RESULTS

At the age of 8 years, levels of HDM allergen Der f1 but not Der p1 were lower in the active than the placebo mattress cover group. In repeated measures analyses, we found a temporary decreased risk of asthma symptoms at the age of 2 years in the intervention group compared to the placebo group and a temporary association between higher HDM allergen exposure at the age of 3 months and more asthma symptoms.

CONCLUSION

Early intervention with mite-impermeable mattress covers is successful in reducing exposure to Der f1; it only temporarily reduces the risk of asthma symptoms and does not reduce the risk of hay fever, eczema, and allergic sensitization.

Characterisation of asthma among adults with and without childhood farm contact

Childhood farm contact is associated with a lower prevalence of sensitisation and allergic rhinitis. Findings have been contradictory for asthma. The aim of the present study was to investigate the differences between farm and nonfarm subjects using objective measurements. A cross-sectional questionnaire study was performed among rural adults aged 18-44 yrs, of which 37% lived on a farm during the first 3 yrs of life and were thus referred to as "farm subjects". Lung function, bronchial hyperresponsiveness (BHR) to methacholine and sensitisation were measured in a random sample. A total of 1,595 subjects were included in the analyses. Among farm subjects, sensitisation against inhalant allergens (odds ratio (OR) 0.7; 95% confidence interval 0.6-0.9), allergic rhinitis (0.5 (0.4-0.8)) and asthma diagnosis (0.7(0.4-1.1)) were less common than among nonfarm subjects. For BHR and lung function, no statistically significant differences were found between the two groups. Stratifying for sensitisation, farm subjects had a lower OR of asthma diagnosis (0.5 (0.3-1.0)) and a nonsignificantly reduced OR of BHR with sensitisation (0.8 (0.5-1.1)). The present study confirmed, using objective measurements, that farm subjects have a lower prevalence of symptoms and asthma diagnosis, while the prevalence of bronchial hyperresponsiveness does not differ.

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.

Do central vacuum cleaners produce less indoor airborne dust or airborne cat allergen, during and after vacuuming, compared with regular vacuum cleaners?

Vacuum cleaners with a central exhaust may lead to lower airborne dust and allergen concentrations compared with regular vacuum cleaners. In 12 houses, equipped with a central vacuum cleaning system, a standardized vacuum cleaning protocol was performed comparing airborne dust and allergen concentrations between the central system and a regular cleaner. Airborne dust concentrations during (104 vs. 95 microg/m(3)) and after vacuum cleaning (38 vs. 36 microg/m(3)) were not significantly different. In houses with a cat, Fel d 1 concentrations were also not significantly different either during (6.12 vs.5.91 ng/m(3)) and after (0.64 vs. 0.91 ng/m(3)) use of the vacuum cleaners. Airborne dust and Fel d 1 concentrations increased considerably during use of both vacuum cleaners. Compared with central vacuum cleaning systems, conventional modern vacuum cleaners do not cause higher airborne dust or cat allergen concentrations during and after use.

PRACTICAL IMPLICATIONS

This study shows that the amount of dust or cat allergen in the air during and after vacuum cleaning is similar when comparing a central vacuum cleaner with a regular vacuum cleaner. Therefore, allergen avoidance advice given to reduce exposure of allergic asthmatic patients to allergens, does not necessarily have to include switching to a central vacuum cleaner.

Risk factors for atopic dermatitis in infants at high risk of allergy: the PIAMA study

BACKGROUND

It has been suggested that the period immediately after birth is a sensitive period for the development of atopic disease.

OBJECTIVE

We investigated whether birth characteristics and environmental factors are associated with the development of atopic dermatitis in the first year of life.

METHODS

Seventy-six children with and 228 without atopic dermatitis, all children of mothers with respiratory allergy or asthma (PIAMA birth cohort study) were included in the study. Atopic dermatitis was defined as a positive history of an itchy skin condition with at least two of the following characteristics: visible dermatitis, history of outer arms/leg involvement, or general dry skin. Multiple logistic regression analysis was performed to study the independent effects of various risk factors.

RESULTS

A birth weight >/=4000 g compared to 3000-4000 g was a significant risk factor for atopic dermatitis (odds ratio (OR)=2.4; 95% CI: 1.1-5.1) as was day care attendance (OR=2.9; 95% CI: 1.5-5.9). Exclusive breastfeeding in the first 3 months was negatively associated with atopic dermatitis (OR=0.6; 95% CI: 0.3-1.2), especially with visible dermatitis (OR=0.4; 95% CI: 0.2-1.0). Gender, gestational age, the presence of siblings or pets, and parental smoking were not significantly associated with atopic dermatitis.

CONCLUSION

This study shows that a high birth weight and day care attendance increase the risk of atopic dermatitis in the first year of life, while exclusive breastfeeding is a protective factor when dermatitis is found on inspection.

Short and long term variability of the interrupter technique under field and standardised conditions in 3-6 year old children

BACKGROUND

The short and long term variability of the interrupter technique was assessed to determine whether interrupter resistance is a stable individual characteristic over time. The effect of field and standardised measurement conditions on the within-subject variability of the interrupter technique was also examined.

METHODS

The interrupter technique was studied under field and standardised conditions in children aged 3-6 years. Under field conditions, five investigators performed the measurements using two different measurement devices in random sequence. Both short term (20-30 minutes) and long term variability (median 38 days) were assessed in 32 children. Under standardised conditions, a single investigator conducted all measurements using a single device; the repeated measurements were conducted at the same time of day in a familiar quiet classroom. Long term variability (median 11 days) was estimated in 15 children. Within-subject standard deviations were estimated by analysis of variance with adjustment for the effects of different investigators and measurement devices on within-subject variability under field conditions.

RESULTS

Under field conditions within-subject standard deviations for short and long term variability were 0.10 kPa/l/s (adjusted 0.10 kPa/l/s) and 0.13 kPa/l/s (adjusted 0.14 kPa/l/s), respectively. Under standardised conditions the within-subject standard deviation for long term variability was 0.10 kPa/l/s.

CONCLUSIONS

Measurement of interrupter resistance under field conditions only slightly increased the within-subject variability compared with standardised conditions. The results indicate that interrupter resistance is a stable individual characteristic over a period of some weeks.

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.

Respiratory infections in infants: interaction of parental allergy, child care, and siblings-- The PIAMA study

OBJECTIVE

To investigate the association between contacts with other children and the development of respiratory infections in the first year of life in children with or without genetic predisposition for allergy.

METHODS

Children (n = 4146) who participate in a prospective birth cohort study (Prevention and Incidence of Asthma and Mite Allergy study) were investigated. Questionnaires were used to obtain information on doctor-diagnosed upper respiratory tract infection (URTI) and lower respiratory tract infection (LRTI), child care attendance, having siblings, family history of allergic disease, and various potential confounders.

RESULTS

Child care attendance in the first year of life was associated with doctor-diagnosed URTI (adjusted odds ratio [AOR]: 2.7; 95% confidence interval [CI]: 2.1-3.4 for large child care facility vs no child care) and doctor-diagnosed LRTI (AOR: 5.6; 95% CI: 3.9-7.9). Having siblings was associated with doctor-diagnosed LRTI (AOR: 2.6; 95% CI: 2.0-3.4). In addition, children who have allergic parents and attend child care or have older siblings have a higher risk of developing doctor-diagnosed LRTI than do children who have nonallergic parents.

CONCLUSIONS

Child care attendance or having siblings increases the risk of developing doctor-diagnosed LRTI in the first year of life to a greater extent in allergy-prone children than in children who are not allergy prone.

Infant respiratory symptoms in relation to mite allergen exposure

The relationship between the Dermatophagoides pteronyssinus (Der p) I content of house dust and the respiratory symptoms reported for young infants was studied. One hundred and four infants, aged 3-15 months, were selected during July-September 1993 through the Dutch postnatal health care service, using a short screening questionnaire to identify mothers with respiratory allergy to house dust and/or pets. Forty-eight were selected from this group of mothers ("high risk" infants) and 56 infants were selected when neither of the parents reported allergy or chronic respiratory symptoms ("low risk" infants). All homes were visited in October 1993. Dust samples were collected from the infant's mattress and from other places in the home, and the Der p I content was measured in dust extracts. The results indicate that on more than half of the mattresses, the Der p I level was over 2,000 ng.g-1, the level suggested to be associated with an increased risk of sensitization. Information on respiratory symptoms ("wheeze" and "prolonged cough") experienced since birth was obtained by questionnaire from one of the parents on the dust sampling day. The occurrence of respiratory symptoms in the infants appeared to be positively related to the Der p I concentration of the dust. Although no objective measurements of respiratory symptoms were available, the results of this study suggest that exposure to mite allergen in early life may lead to respiratory symptoms that are suggestive of airway obstruction in the first year of life.

Der p I concentrations in mattress surface and floor dust collected from infants' bedrooms

BACKGROUND

Allergen exposure in early childhood is thought to be important for sensitization and subsequent development of asthma. Not much is known, however, about exposure of young children to allergens in the home.

OBJECTIVES

This study was designed to document dust mite allergen exposure in young children, and to determine whether infants from atopic mothers (= 'high-risk' infants) are exposed to lower concentrations of house dust mite allergen than infants from non-atopic parents (= 'low-risk' infants).

METHODS

Dust samples were taken in the homes of 104 infants (48 'high-risk' and 56 'low-risk' infants, selected by questionnaire) aged 3-15 months, from floors in different rooms and from the child's mattress surface.

RESULTS

The majority of the infants were found to be exposed to Der p I concentrations of more than 2000 ng/g in dust collected from the surface of their mattresses. Lower Der p I concentrations were found in mattress surface dust from the beds of infants from atopic mothers than of infants from non-atopic parents. Also, lower Der p I concentrations were found in floor dust from the homes of infants from atopic mothers. Infant beds equipped with new mattresses, new blankets and top plastic sheeting had significantly lower Der p I concentrations than beds equipped with used mattresses and blankets, without top plastic sheeting.

CONCLUSIONS

Young children in the Netherlands are exposed to significant concentrations of Der p I in mattress surface dust. Allergic parents appear to provide their children with environments somewhat less rich in mite allergen than non-allergic parents.

Damp housing and childhood respiratory symptoms: the role of sensitization to dust mites and molds

In 1990, a case-control study was conducted in the Netherlands into the association between damp housing, childhood respiratory symptoms, and sensitization to house dust mites and mold allergens. In this study, 259 children with chronic respiratory symptoms and 257 control children were involved. Total serum immunoglobulin E (IgE) and specific IgE against house dust mites and a mixture of molds were determined. A visual inspection for signs of home dampness was performed in all homes. A questionnaire was given to the parents of the children to elicit information about the presence of signs of dampness in the previous 2 years and about risk factors for childhood respiratory disease. In the case group, 94 children had elevated serum IgE levels to house dust mites and 24 children to the mixture of molds. In the control group, house dust mite allergy was found in 31 children and mold allergy in two children. In a crude analysis, cases were slightly more likely to have been living in homes where damp or mold was reported or observed than were the controls. In cases as well as controls, home dampness was associated with increased sensitization to dust mites and molds. There was no relation between home dampness and case-control status after stratification for sensitization, however. Restriction of the analysis to cases with elevated serum IgE levels against dust mites and/or molds, and to controls without elevated serum IgE, increased the odds ratios, and several became significant at p < 0.05. This supports a connection between damp housing and sensitization to dust mites and/or molds and childhood respiratory symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Fungal propagules in house dust. II. Relation with residential characteristics and respiratory symptoms

As part of a case-control study on the relation between home dampness and respiratory symptoms of children, house-dust samples were collected from bedroom floors and mattresses in 60 homes in The Netherlands. The house-dust samples were analyzed for the presence of fungal propagules by plating 30 mg of dust directly onto DG18 agar. A checklist and questionnaire were used to obtain information on the home characteristics and occupant behavior that may have an effect on the presence of fungal propagules in house dust. The geometric mean (GM) numbers of colony-forming units (CFU)/g dust collected from the floors was 8990. The number of CFU/g dust was significantly higher in dust from carpeted floors than in dust from smooth floors (GM, respectively, 12,880 CFU/g dust and 3530 CFU/g dust). The GM number of CFU/g dust collected from mattresses was 6760. Overall, the mean numbers of CFU/g dust collected from floors and mattresses were higher in bedrooms where damp spots mold growth, or both were observed. However, these differences were not statistically significant. The relation between home characteristics and the number of CFU/g dust of the most frequently isolated mold species (n = 17), including Alternaria alternata, Cladosporium cladosporioides, Penicillium brevicompactum, and Scopulariopsis brevicaulis, was also investigated. Only the type of flooring had a significant and consistent effect on the number of CFU/g floor dust of the different mold species.(ABSTRACT TRUNCATED AT 250 WORDS)

[House dust mite allergens and COPD in children; a case-control study]

OBJECTIVE

To determine the relationship between mite allergen (Der p I) concentrations in house dust and presence of chronic respiratory symptoms in children.

DESIGN

Case control study.

SETTING

The provinces of Gelderland and North-Holland in the Netherlands.

METHOD

Questionnaires were handed to pupils of 38 schools to take home; about 6000 were returned (80% response). A home visit was paid to 259 children with chronic respiratory symptoms ('cases') and to 257 symptom-free 'control' children. Using an enzyme immunoassay the Der p I concentrations of living room floor dust, bedroom floor dust and mattress dust were determined. Specific IgE was determined in serum.

RESULTS

Der p I concentrations higher than 2000 ng/g were found in 86% of the dwellings and concentrations higher than 10,000 ng/g in 55%. Cases were exposed to lower Der p I concentrations than controls. However, cases sensitised to dust mites were exposed to higher Der p I concentrations than non-sensitised cases, both living in homes where no allergen avoidance measures had been taken in the past.

CONCLUSION

Exposure to Der p I in the home was associated with sensitisation to dust mites in children with chronic respiratory symptoms living in homes where no allergen avoidance measures had been taken.