Indoor environmental factors associated with house-dust-mite allergen (Der p 1) levels in south-eastern Australian houses

Prevalence, Risk Factors and Impacts Related to Mould-Affected Housing: An Australian Integrative Review

In response to an Australian governmental inquiry into biotoxin-related illness, the purpose of this integrative review is to bring together the current state of evidence on the prevalence, risk factors and impacts related to mould-affected housing in an Australian context, in order to inform building, housing and health research, practice and policy. The robust integrative review methodology simultaneously sought quantitative and qualitative studies and grey literature from multiple disciplines, identifying only 45 studies directly relating to Australian housing and indoor mould. Twenty-one studies highlight negative health impacts relating to indoor residential mould, with asthma, respiratory, allergy conditions and emerging health concerns for chronic multiple-symptom presentation. The majority of studies reported risk factors for indoor mould including poor housing conditions, poor-quality rental accommodation, socioeconomic circumstance, age-related housing issues and concerns for surface/interstitial condensation and building defects in newer housing. Risks for indoor mould in both older and newer housing raise concerns for the extent of the problem of indoor mould in Australia. Understanding the national prevalence of housing risks and “root cause” associated with indoor mould is not conclusive from the limited existing evidence. Synthesis of this evidence reveals a lack of coverage on: (1) national and geographical representation, (2) climatical coverage, (3) housing typologies, (4) housing defects, (5) maintenance, (6) impact from urbanisation, and (7) occupant’s behaviour. This integrative review was key in identifying emerging housing and health concerns, highlighting gaps in data and implications to be addressed by researchers, practice and policy and acts as a comprehensive holistic review process that can be applied to other countries.

The Role of Dust Mites in Allergy

House dust mites are an unsurpassed cause of atopic sensitization and allergic illness throughout the world. The major allergenic dust mites Dermatophagoides pteronyssinus, Dermatophagoides farinae, Euroglyphus maynei, and Blomia tropicalis are eight-legged members of the Arachnid class. Their approximately 3-month lifespan comprises egg, larval, protonymph, tritonymph, and adult stages, with adults, about one fourth to one third of a millimeter in size, being at the threshold of visibility. The geographic and seasonal distributions of dust mites are determined by their need for adequate humidity, while their distribution within substrates is further determined by their avoidance of light. By contacting the epithelium of the eyes, nose, lower airways, skin, and gut, the allergen-containing particles of dust mites can induce sensitization and atopic symptoms in those organs. Various mite allergens, contained primarily in mite fecal particles but also in shed mite exoskeletons and decaying mite body fragments, have properties that include proteolytic activity, homology with the lipopolysaccharide-binding component of Toll-like receptor 4, homology with other invertebrate tropomyosins, and chitin-cleaving and chitin-binding activity. Mite proteases have direct epithelial effects including the breaching of tight junctions and the stimulation of protease-activated receptors, the latter inducing pruritus, epithelial dysfunction, and cytokine release. Other components, including chitin, unmethylated mite and bacterial DNA, and endotoxin, activate pattern recognition receptors of the innate immune system and act as adjuvants promoting sensitization to mite and other allergens. Clinical conditions resulting from mite sensitization and exposure include rhinitis, sinusitis, conjunctivitis, asthma, and atopic dermatitis. Systemic allergy symptoms can also occur from the ingestion of cross-reacting invertebrates, such as shrimp or snail, or from the accidental ingestion of mite-contaminated foods. Beyond their direct importance as a major allergen source, an understanding of dust mites leads to insights into the nature of atopy and of allergic sensitization in general.

How clean is your house? A study of house dust mites, allergens and other contents of dust samples collected from households

Household dust contains an array of constituents, including house dust mites (HDM) and the HDM allergen, Der p 1, which can cause sensitivities such as asthma and eczema. Vacuuming can help alleviate symptoms, yet little is understood about cleaning behaviour in different households. This pilot study investigated the contents of dust from four household types (students; over 65 s; and families with and without pets). This was then related to cleaning behaviours and perceptions of cleanliness. Our investigation found that HDMs and Der p 1 were present in all households and sampling locations, including participants' cars. The median Der p 1 was greatest in the living room, though results varied. Demographic group was a determinant for the number of human and pet hairs present in dust. Surprisingly, vacuuming was the most disliked task overall. This information requires consideration when developing cleaning products and advising individuals with dust-related health issues.

Relationship between, Lifestyle, Mold and Sick Building Syndromes in Newly Built Dwellings in Japan

To investigate the relationships among Sick Building Syndrome (SBS) symptoms, we conducted a questionnaire and an indoor environment mold survey in a sample of newly built dwellings in Japan. The questionnaire included questions on SBS symptoms and lifestyle and a mold survey conducted in the living room of each dwelling. The odds ratios (OR) for insufficient sleep were 3.58 in males and 2.57 (weighted for SBS symptoms; W) in females, 0.38 (W) for alcohol consumption in males, and 0.10 (W) for working hours in females. The ORs for total molds were 2.90 and 2.90 (W): 2.25 (W) for Cladosporium cladosporioides, 3.60 and 7.69 (W) for Penicillium sp. in females, and 4.08 and 8.82 (W) for Alternaria alternata in males. These results suggest that the presence of Penicillium sp. in females and Alternaria alternata in males increases the risk of SBS, whereas sufficient sleep, moderate alcohol consumption for males, and fewer working hours for females might alleviate SBS symptoms.

Concentration and determinants of molds and allergens in indoor air and house dust of French dwellings

Molds and allergens are common indoor biocontaminants. The aims of this study were to assess the concentrations of common molds in indoor air and floor dust and the concentrations of house dust mite, cat and dog allergens in mattress dust in French dwellings, and to assess predictors of these concentrations. A sample of 150 houses in Brittany (western France) was investigated. Airborne Cladosporium and Penicillium were detected in more than 90% of the dwellings, Aspergillus in 46% and Alternaria in only 6% of the housings. Regarding floor dust samples, Cladosporium and Penicillium were detected in 92 and 80% of the housings respectively, Aspergillus in 49% and Alternaria in 14%. House dust mite allergens Der p1 and Der f1 were detected in 90% and 77% of the mattress dust samples respectively and Can f1 and Fel d1 in 37% and 89% of the homes. Airborne and dustborne mold concentrations, although not statistically correlated (except for Aspergillus) shared most of their predictors. Multivariate linear models for mold levels, explaining up to 62% of the variability, showed an influence of the season, of the age of the dwelling, of aeration habits, presence of pets, smoking, signals of dampness, temperature and relative humidity. Allergens in the dust of the mattress were strongly related to the presence of pets and cleaning practices of bedsheets, these factors accounting for 60% of the variability. This study highlights ubiquitous contamination by molds and underlines complex interaction between outdoor and indoor sources and factors.

Respiratory allergy caused by house dust mites: What do we really know?

The house dust mite (HDM) is a major perennial allergen source and a significant cause of allergic rhinitis and allergic asthma. However, awareness of the condition remains generally low. This review assesses the links between exposure to HDM, development of the allergic response, and pathologic consequences in patients with respiratory allergic diseases. We investigate the epidemiology of HDM allergy to explore the interaction between mites and human subjects at the population, individual, and molecular levels. Core and recent publications were identified by using "house dust mite" as a key search term to evaluate the current knowledge of HDM epidemiology and pathophysiology. Prevalence data for HDM allergen sensitization vary from 65 to 130 million persons in the general population worldwide to as many as 50% among asthmatic patients. Heterogeneity of populations, terminology, and end points in the literature confound estimates, indicating the need for greater standardization in epidemiologic research. Exposure to allergens depends on multiple ecological strata, including climate and mite microhabitats within the domestic environment, with the latter providing opportunity for intervention measures to reduce allergen load. Inhaled mite aeroallergens are unusually virulent: they are able to activate both the adaptive and innate immune responses, potentially offering new avenues for intervention. The role of HDM allergens is crucial in the development of allergic rhinitis and asthma, but the translation of silent sensitization into symptomatic disease is still incompletely understood. Improved understanding of HDMs, their allergens, and their microhabitats will enable development of more effective outcomes for patients with HDM allergy.

Early life environmental predictors of asthma age-of-onset

Prevention strategies that delay the onset of asthma may improve clinical outcomes. To identify early life environmental exposures associated with asthma age-of-onset and potential genetic modifiers of these exposures, we studied 1085 subjects with physician-diagnosed asthma and disease onset at or after age two. Subjects reported retrospectively on their exposure to 17 environmental factors before the age of two. The presence of individual or combinations of these early life exposures was then tested for association with variation in asthma age-of-onset. For exposures significantly associated with age-of-onset, we tested if 26 single nucleotide polymorphisms (SNP) with an established association with allergic disease significantly modified the effect of the exposure. Five environmental exposures were significantly associated with variation in asthma age-of-onset after correction for multiple testing: carpet at home (P = 6 × 10⁻⁵), a serious chest illness (P = 10⁻⁴), father a cigarette smoker (P = 6 × 10⁻⁴) and direct exposure to father's smoking (P = 3 × 10⁻⁴). Individuals with early childhood asthma onset, between the ages of two and six, were 1.4-fold (CI 1.1–1.9) more likely to report having lived in a house with carpet and 2.1-fold (CI 1.3–3.5) more likely to report suffering a serious chest illness before the age of two, than asthmatics with later disease onset. We further found these individual risks to increase to 3.2-fold (CI 1.7–6.0) if carpet exposure and suffering a serious chest illness co-occurred before age two. Paternal smoking exposures were less likely to be reported by asthmatics with early when compared to later disease onset (OR 0.5, CI 0.3–0.7). There were no significant SNP interactions with these environmental exposures after correction for multiple testing. Our results suggest that disease onset in individuals at a high-risk of developing asthma can potentially be delayed by avoiding exposure to carpet at home and preventing serious chest illnesses during the first 2 years of life.

Relationships between mite allergen levels, mold concentrations, and sick building syndrome symptoms in newly built dwellings in Japan

This study investigated the possible relationships between exposures to mite allergen and airborne fungi with sick building syndrome (SBS) symptoms for residents living in newly built dwellings. We randomly sampled 5709 newly built dwellings in six prefectures from northern to southern Japan. A total of 1479 residents in 425 households participated in the study by completing questionnaire surveys and agreeing to environmental monitoring for mite allergen (Der 1), airborne fungi, aldehydes, and volatile organic compounds. Stepwise logistic regression analyses adjusted for confounders were used to obtain odds ratios (OR) of mite allergen and fungi for SBS symptoms. Der 1 had a significantly high OR for nose symptoms. Rhodotorula had a significantly high OR for any symptoms, and Aspergillus had significantly high OR for eye symptoms. However, the total colony-forming units had a significantly low OR for throat and respiratory symptoms. Eurotium had a significantly low OR for skin symptoms. In conclusion, dust-mite allergen levels and indoor airborne Rhodotorula and Aspergillus concentrations may result in SBS symptoms in newly built dwellings.

PRACTICAL IMPLICATIONS

Various factors can cause sick building syndrome symptoms. This study focused on biologic factors such as dust-mite allergen and airborne fungi in newly built dwellings in Japan. Dust-mite allergen levels were significantly associated with higher rates of nose symptoms, airborne Rhodotorula concentrations were significantly associated with higher rates of any symptoms, and Aspergillus concentrations were significantly associated with higher rates of eye symptoms. Measures should be taken to reduce mite allergen levels and fungal concentrations in these dwellings.

Relationship between selected indoor volatile organic compounds, so-called microbial VOC, and the prevalence of mucous membrane symptoms in single family homes

Microorganisms are known to produce a range of volatile organic compounds, so-called microbial VOC (MVOC). Chamber studies where humans were exposed to MVOC addressed the acute effects of objective and/or subjective signs of mucosal irritation. However, the effect of MVOC on inhabitants due to household exposure is still unclear. The purpose of this epidemiological study was to measure indoor MVOC levels in single family homes and to evaluate the relationship between exposure to them and sick building syndrome (SBS). All inhabitants of the dwellings were given a self-administered questionnaire with standardized questions to assess their symptoms. Air samples were collected and the concentrations of eight selected compounds in indoor air were analyzed by gas chromatography/mass spectrometry - selective ion monitoring mode (GC/MS-SIM). The most frequently detected MVOC was 1-pentanol at a detection rate of 78.6% and geometric mean of 0.60 microg/m(3). Among 620 participants, 120 (19.4%) reported one or more mucous symptoms; irritation of the eyes, nose, airway, or coughing every week (weekly symptoms), and 30 (4.8%) reported that the symptoms were home-related (home-related symptoms). Weekly symptoms were not associated with any of MVOC, whereas significant associations between home-related mucous symptoms and 1-octen-3-ol (per log(10)-unit: odds ratio (OR) 5.6, 95% confidence interval (CI): 2.1 to 14.8) and 2-pentanol (per log(10)-unit: OR 2.3, 95% CI: 1.0 to 4.9) were obtained after adjustment for gender, age, and smoking. Associations between home-related symptoms and 1-octen-3-ol remained after mutual adjustment. However, concentrations of the selected compounds in indoors were lower than the estimated safety level in animal studies. Thus, the statistically significant association between 1-octen-3-ol may be due to a direct effect of the compounds or the associations may be being associated with other offending compounds. Additional studies are needed to evaluate these possibilities.

Housing and allergens: a pooled analysis of nine US studies

BACKGROUND

Housing conditions can contribute to allergen exposures that are linked to asthma, but little is known about which of those conditions are most likely to predict high levels of allergens in settled house dust.

METHODS

We pooled allergen, housing condition, occupant behavior, demographic, and other data from nine asthma studies (n=950 homes in 6 US cities). Dust mite (Der f 1 or Der p 1), cockroach (Bla g 1 or Bla g 2), mouse (Mus m 1), cat (Fel d 1) and dog (Can f 1) allergens were measured in settled dust from kitchens or bedrooms, and concentrations were categorized according to previously published asthma symptom thresholds. We calculated odds ratios (OR) using logistic regression to identify those housing conditions and occupant behaviors that were associated with clinically significant allergen levels, after adjusting for numerous confounding variables.

RESULTS

The adjusted results show that high cockroach allergen was associated with cracks or holes in walls (OR=2.1), high dust mite allergen was associated with mold odor (OR=2.5), housing built before 1951 (OR=2.1), and single-family home with slab on grade (OR=1.9); and mouse allergen was associated with rodent control or signs of rodents (OR=3.62) and inversely associated with presence of a cat (OR=0.20). Water leaks and below average housekeeping had unadjusted high odds ratios for high cockroach allergen.

CONCLUSION

We have identified a number of housing conditions that are consistently associated with increased allergen dust concentrations. This study indicates that screening for housing-based asthma triggers should include presence of cats, dogs, cockroaches, or rodents; water leaks; mold or mold odor; holes or cracks in walls; and below average housekeeping. Single family houses that have basements or crawl spaces or are built before 1951 are also important predictors for increased allergens in housing.

Relationship between sick building syndrome and indoor environmental factors in newly built Japanese dwellings

OBJECTIVES

Indoor air contaminants and dampness in dwellings have become important environmental health issues. The aim of this study is to clarify which factors are related to sick building syndrome (SBS) in newly built dwellings at Hokkaido, Japan, through a comprehensive evaluation of the indoor environment and validated sick building symptom questionnaires.

METHODS

The symptoms of 343 residents in 104 detached houses were surveyed by standardized questionnaires, and the concentrations of formaldehyde, acetaldehyde, volatile organic compounds (VOCs), airborne fungi, and dust mite allergen in their living rooms were measured. By summing the presence or absence of the five dampness indicators (condensations, mold growth, moldy odor, high air humidity of the bathroom, water leakage), a dampness index was calculated.

RESULTS

SBS symptoms were found in 21.6% of surveyed individuals. In a fully adjusted multivariate logistic regression analysis, the dampness index [odds ratio (OR) = 1.50; 95% confidence interval (CI): 1.06-1.11], log formaldehyde (OR = 23.79, 95% CI: 2.49-277.65), and log alpha-pinene (OR = 2.87, 95% CI: 1.36-6.03) had significantly higher ORs for SBS symptoms. However, other VOCs, airborne fungi, and dust mite allergen did not have significantly higher ORs.

CONCLUSION

Dampness, formaldehyde, and alpha-pinene were significantly related to SBS symptoms in newly built dwellings. We should, therefore, take measures to reduce the chemicals and dampness in dwellings.

Seasonal trends in house dust mite allergen in children's beds over a 7-year period

BACKGROUND

House dust mite (HDM) allergy is closely linked to the expression of asthma and other allergic diseases. Understanding factors influencing variation in allergen may help in controlling allergic disease. The objective of this study was to investigate the effects of seasonal changes in climate, type of bed used in very early childhood and anti-mite interventions on HDM allergen concentration.

METHODS

Participants were enrolled in a randomized-controlled trial of HDM avoidance. Der p 1 was measured in dust samples from children's beds on 13 occasions, from birth to age 5 years, between 1997 and 2004. Bed types were categorized as bassinette, cot or bed. The effects of study month, type of bed and intervention group on HDM allergen concentration were estimated by multiple linear regression. The relation between climatic variables and HDM allergen concentration was investigated using a polynomial distributed lag model.

RESULTS

House dust mite allergen concentrations were initially low in cots and bassinettes in 1997/1998, peaked in bassinettes and beds between 1999 and 2001 and then slowly declined during the period 2002/2004. Seasonal fluctuations occurred with minima in summer and two- to threefold higher maxima during late autumn. Allergen peaks were correlated with relative humidity peaks 2 months previously. Seasonal changes in allergen were not affected by the HDM avoidance intervention.

CONCLUSIONS

House dust mite allergen concentrations in Sydney beds fluctuate approximately two- to threefold on an annual cycle, partly determined by relative humidity, with peaks in late autumn and minima in summer. Fluctuations of this magnitude might be sufficient to influence asthma symptoms.

Dust weight and asthma prevalence in the National Survey of Lead and Allergens in Housing (NSLAH)

BACKGROUND

Settled dust has been used in studies to assess exposures to allergens and other biologically active components, but it has not been considered in the aggregate in relation to respiratory health outcomes in the general population.

OBJECTIVE

We addressed whether total house dust weight, an index of total dust exposure, was associated with respiratory health outcomes in the National Survey of Lead and Allergens in Housing (1998-1999) (NSLAH).

METHODS

NSLAH was a cross-sectional survey designed to represent permanently occupied housing units in the United States. In each household, a questionnaire was administered and settled dust was vacuumed from five locations. Linear regression models were used to identify predictors of dust weight; logistic regression models were used to examine the relationship between dust weight and asthma and wheeze.

RESULTS

Dust weight samples were available for 829 households, and survey information was available for 2,456 participants (children and adults). Lower income, older homes, household pets, having a smoker in the house, and less frequent cleaning predicted higher dust weight levels in U.S. households. Higher levels of dust weight were associated with greater odds of current asthma and wheeze. The strongest associations were seen for wheeze [adjusted odds ratio (OR) = 1.99; 95% confidence interval (CI), 1.21-3.28 for bedroom bed dust; OR = 2.81; 95% CI, 1.52-5.21 for upholstery dust). These associations persisted when adjusting for allergen and endotoxin exposures.

CONCLUSIONS

Dust weight, an index of total dust exposure in the home, may contribute to respiratory outcomes independently of the exposure to specific components.

Influence of mattress characteristics on house dust mite allergen concentration

BACKGROUND

Exposure to a high level of house dust mite allergens (HDMAs) is considered as a risk factor for HDM sensitization and development of asthma in genetically disposed people. Mattresses are one of the most important sources of HDMA in people's living environment.

OBJECTIVE

The aim of this study was to evaluate the association between mattress characteristics and HDMA concentrations on mattresses.

METHODS

Dust samples of mattress surfaces were taken to evaluate the level of Der p 1 allergen. All participants filled in a questionnaire about the type of mattress, the type of covering (upper layer) of the mattress, dwelling characteristics and cleaning habits. Humidity and temperature of the bedroom were measured at the time of dust sampling.

RESULTS

One hundred and sixty-eight questionnaires were filled in. Synthetic upper layer of the mattress was associated with a higher level of Der p 1 compared with cotton upper layer (2.6 vs. 0.8 microg/g Der p 1). Moreover, higher relative humidity (RH) was associated with significant higher concentrations and density of Der p 1.

CONCLUSIONS

Two factors were associated with lower levels of Der p 1 found on mattresses, namely: a cotton upper layer of the mattress compared with a layer of synthetic material and lower RH at the time of sampling. As far as we know, the association between type of upper layer and concentration of Der p 1 has not been described before and could lead to the formulation of practical advices in order to reduce HDMA concentrations on mattresses.

Symptoms in relation to chemicals and dampness in newly built dwellings

OBJECTIVES

As the airtightness of dwellings has recently increased, problems associated with indoor air pollution and dampness have become important environmental health issues. The aim of this study was to clarify whether symptoms in residents living in newly built dwellings were related to chemicals and dampness.

METHODS

Symptoms of 317 residents were surveyed by standardized questionnaires, and the concentrations of formaldehyde, acetaldehyde, and 17 volatile organic compounds (VOCs) in their homes were measured. Dampness (condensation on window panes and/or walls, and mold growth) was identified by questionnaires given to the householders or their partners.

RESULTS

Some VOCs (toluene, butyl acetate, ethylbenzene, alpha-pinene, p-dichlorobenzene, nonanal, and xylene) were significantly related to the symptoms, and the sum of all VOCs (all identified VOCs) was significantly related to throat and respiratory symptoms [odds ratio (OR) for eye symptoms =2.4; 95% confidence interval (CI) 1.0-5.5], although the concentrations of VOCs were relatively low. As for the dampness index, condensation on window panes and/or walls was related to all symptoms, and mold growth was related to all symptoms except skin, throat and respiratory and general symptoms. As the number of dampness signs increased, the ORs increased for the symptoms except general symptoms (OR for nose symptoms = 4.4, 95% CI 1.6-11.9).

CONCLUSION

Both VOCs and dampness were significantly related to symptoms. We should take measures to reduce the concentrations of VOCs, dampness and microbial growth in dwellings.

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.

Childhood asthma management and control. Analysis of the Student Lung Health Survey (SLHS) database, Canada 1996

The objective of this study was to estimate the severity of childhood asthma in Canada, identify the effects of asthma interventions in different target groups, and to profile asthma management and control practices by geographic area, sex, age, and severity groups.

METHODS

The SLHS was conducted as a stratified and multi-staged cluster survey across Canada in 1996. It included a total of 136 public, private and separate schools in nine health units (Prince Edward Island, Halifax, Sherbrooke, Kingston, Guelph, Winnipeg, Saskatoon, Edmonton, and Kelowna). The target study population was schoolchildren aged 5 to 19 years. Descriptive analyses were used to calculate the severity of childhood asthma for the different groups. Logistic regression was then employed to measure the quality of asthma intervention and control. Multivariate logistic regression was also used to compare the severity and treatment of asthma with age, sex and lifestyle, living and housing conditions. Using existing Clinical Practice Guidelines as a reference, the study also evaluated the effectiveness of interventions such as treatment, and asthmatic education.

RESULTS

Based on the Canadian Consensus Recommendations of definition of asthma control, among all 5-19 years old students, 39.9% were well controlled, 33.8% were acceptably controlled and 26.3% were poor controlled. The rates of intermittent and mild asthma were 44.8% and 11.6% compared with moderate (15.3%) and severe (0.9%). Students with asthma reported receiving more advantaged information from a demonstration of inhaler users (OR = 7.51, 95% CI = 5.65-8.94), during a medical visits (OR = 6.33, 95% CI = 5.11-7.83), from the pamphlet/brochures (OR = 6.22, 95% CI = 5.05-7.76) or from a demonstration of the correct use of medicine (OR = 5.62, 95% CI = 4.62-6.82). More students visited a family doctor (40.3%, OR = 5.52, 95% CI = 4.95-6.64) and medical specialists (31.0%, OR = 3.69, 95% CI = 2.58-4.78) than other specialist when they had respiratory problems.

CONCLUSIONS

The results of the SLHS study demonstrated variations in the management and control of childhood asthma across Canada. The interventions and the practice guidelines for asthma control are useful for preventing and controlling asthma. These findings provide indications of interventions that are being used for the control of asthma in Canada.

Predictors of high house dust mite allergen concentrations in residential homes in Sydney

BACKGROUND

In parts of coastal Australia, house dust mite allergen concentrations in homes are often very high with at least 80% of homes in Sydney exceeding concentrations of 10 microg of allergen per gram of fine dust. In this study, we report the relation between characteristics of the home environment and house dust mite allergen concentrations at three sites in Sydney homes.

METHODS

A total of 616 families were recruited as part of the Childhood Asthma Prevention Study (CAPS). Information about the home environment and structural aspects of the home was collected using a questionnaire. Samples of dust were collected from the parents' bed, the bedroom floor and the living room floor and assayed for Der p 1.

RESULTS

A total of 68% of participants' beds, 65% of bedroom floors and 56% of living room floors had Der p 1 concentrations above 10 microg/g, with the highest concentrations of allergen in the bed. The most significant predictor of high Der p 1 concentrations in the bed and floors was the age of the home. We also found that beds with mattresses over two years old and with woollen or synthetic blankets or synthetic quilts had higher Der p 1 concentrations. Carpeted floors had higher Der p 1 concentrations than hard floors.

CONCLUSION

The finding that high Der p 1 allergen concentrations in homes with carpets and older mattresses indicates that control strategies directed at these sources are likely to be effective in reducing exposure. Alternatives such as the use of house dust mite impermeable mattress encasings on older mattresses may also be effective in reducing exposure.

Predictors of house-dust-mite allergen concentrations in dry regions in Australia

BACKGROUND

House-dust-mite allergen content differs between houses and is thought to be a function of the housing characteristics and furnishing choices that affect indoor microclimate and mite proliferation. The importance of these features may differ with regional climates.

METHODS

Concentrations of mite allergen were analysed as a function of housing features. Information on housing features was collected by questionnaire in 50 houses in two towns in a dry inland region of Australia. Mite allergen (Der p 1) was measured by ELISA in dust samples collected on five occasions over 2 years from beds and floors.

RESULTS

Der p 1 was detected in all houses. Many housing features did not influence mite allergen concentrations. However, the presence of evaporative cooling increased mite allergen by 3.34-fold in beds (P=0.007) and 3.94-fold in floors (P=0.003). Mite allergen was threefold higher in mattresses >5 years old, and synthetic and feather duvets tended to have higher and lower levels of mite allergen, respectively.

CONCLUSIONS

In houses in dry, inland regions of Australia, evaporative cooling and older mattresses are associated with higher concentrations of mite allergen. Alternative forms of air conditioning to evaporative cooling may be useful for control of mite allergen in dry regions.

The importance of housing characteristics in determining Der p 1 levels in carpets in New Zealand homes

BACKGROUND

A previous study of homes in Wellington, New Zealand showed that having carpets on floors was the most important determinant of floor Der p 1 levels, but there was much unexplained variability between houses in carpet levels.

OBJECTIVE

To determine to what extent housing characteristics might explain this variability in Der p 1 levels between houses.

METHODS

We returned to a selection of houses with carpets and sampled living room dust from 1 square metre for 1 min and from the whole floor at 5 m(2) per min. Der p 1 levels were estimated by double monoclonal antibody ELISA and are expressed as geometric mean microg/g and microg/m(2) (95% confidence intervals). Questionnaires were used to collect information on housing characteristics.

RESULTS

Der p 1 levels were significantly higher in the 1 square metre sample (40.0, 31.9-50.2 microg/g; 53.4, 41.4-68.9 microg/m(2)) than in the whole room (25.8, 21.3-31.1 microg/g; 5.3, 3.8-7.4 microg/m(2)). However, results from the different sampling methods were correlated (r = 0.51, P = 0.001 for microg/g and r = 0.58, P = 0.001 for microg/m(2)). After controlling for possible confounders, houses with insulation or a room or garage below the living room had approximately half the Der p 1 concentration (P = 0.05 for both samples) and the amount of Der p 1 per m(2) (P = 0.004 for the 1 square meter sample, P = 0.06 for the whole room sample) than houses without these features. Having more than two children was associated with higher levels of Der p 1 in 1 square meter, significant (P = 0.05) for microg/m(2). Carpet underlay less than 8 mm thick was associated with an almost 3-fold increase in microg/m(2) Der p 1 (P = 0.03) and a 1.6-fold increase in microg/g Der p 1 (P = 0.08) in the whole room sample, when compared with thicker carpet underlays.

CONCLUSION

The presence of insulation is the single most important housing characteristic explaining the between-house variability in Der p 1 levels on carpeted living room floors.

Increased risk of allergy in children due to formaldehyde exposure in homes

BACKGROUND

Formaldehyde levels were measured in 80 houses in the Latrobe Valley, Victoria, Australia. An association between exposure to formaldehyde and sensitization to common aeroallergens has been suggested from animal trials, but no epidemiologic studies have tested this hypothesis.

METHODS

A total of 148 children 7-14 years of age were included in the study, 53 of whom were asthmatic. Formaldehyde measurements were performed on four occasions between March 1994 and February 1995 with passive samplers. A respiratory questionnaire was completed, and skin prick tests were performed.

RESULTS

The median indoor formaldehyde level was 15.8 microg/ m3(12.6ppb), with a maximum of 139 microg/m3 (111 ppb). There was an association between formaldehyde exposure and atopy, and the adjusted odds ratio was 1.40 (0.98-2.00, 95% CI) with an increase in bedroom formaldehyde levels of 10 microg/m3. Furthermore, more severe allergic sensitization was demonstrated with increasing formaldehyde exposure. On the other hand, there was no significant increase in the adjusted risk of asthma or respiratory symptoms with formaldehyde exposure. However, among children suffering from respiratory symptoms, more frequent symptoms were noted in those exposed to higher formaldehyde levels.

CONCLUSIONS

Low-level exposure to indoor formaldehyde may increase the risk of allergic sensitization to common aeroallergens in children.