Dust Mite Allergen Levels Research Articles

Does a multifaceted environmental intervention alter the effect of asthma among inner-city children?

Rationale To reduce asthma symptoms in 5-12 year old children through a multifaceted environmental/educational intervention. Methods Changes in indoor allergen levels and asthma severity scores (summary score of symptoms, activity limitations, medication use, hospitalization and emergency department [ED] use) were compared over 14 months between an intervention and delayed intervention (“control”) groups in a prospective, randomized field trial. Intervention group households had dust mite covers put on the child's sleeping surfaces, received a professional house cleaning, had roach bait and trays placed appropriately along with instructions in their monitoring, and received customized information about common allergens avoidance. Results Of 981 eligible subjects presenting to the ED, 410 (42%) were enrolled; 161 (40%) completed baseline activities and were randomized: 84 to intervention and 77 to control. At study's end, control children compared to baseline had a 163% increase in dust mite levels, while the intervention group levels were stable. There was no change in the overall asthma severity scores, however, relative to baseline, the median functional severity score (FSS) component declined more in the intervention (33% versus 20%) than the control group. The median FSS for the intervention group showed a 25% improvement compared to the control group (p<.01). No significant differences were observed between groups for medication use, ED visits or hospitalization. Conclusions Dust mite allergen levels did not increase for the intervention group and the FSS indicated improvement without changing the overall asthma severity score. The interventions probably contributed to improvements in the allergenic environment and the function of the children.

Endotoxin and house dust mite allergen levels on synthetic and buckwheat pillows.

Pillows are known to contain significant levels of indoor allergens and endotoxin, that are of importance to house dust mite sensitized asthmatics. Buckwheat pillows are commonly used in Korea. We studied the levels of the house dust mite allergen, Der f 1, and endotoxin on new synthetic and buckwheat pillows and their accumulation over three months. Endotoxin levels were significantly higher on new buckwheat pillows compared to synthetic pillows; geometric mean levels (95% CI) were 60,950 EU/g (30,270-122,700) and 4,887 EU/g (2,570-9,311) respectively (p<0.001). No Der f 1 was detected on the new pillows. After three months Der f 1 levels were similar on buckwheat and synthetic pillows, geometric mean levels (95% CI) were 1.16 µg/g (0.02-8.13) and 1.08 µg/g (0.19-1.68) respectively. These results indicate that buckwheat pillows are a source of very high endotoxin levels that may be of relevance to asthma severity of atopic asthmatics.

Distribution of house dust mite allergen: comparing house dust mite allergen levels in dust samples collected from different sites on living room floors with smooth coverings.

The distribution of house dust mite allergen (Der p1) in living rooms with smooth floor coverings, as measured in the middle compared with the border of the floor was investigated. It was hypothesized that activity causes displacement of Der p1, from the middle towards the border. Dust samples from the middle and border of 50 floors with smooth coverings were collected and analysed on Der p1 content in a standardized way. The Der p1 exposure expressed as per unit area (ng/m2) showed that border samples contained significantly more Der p1 compared with middle samples (median: 2.57 vs 0.27, respectively, P = 0.023). Presence of pets and presence of more than two inhabitants increased the difference. When expressed as per unit weight of dust (ng/g), significant differences were only detected when comparing Der p1 content of samples collected in households with three or more inhabitants [median: 2 (border) vs 53 (middle), respectively; P = 0.035]. The Der p1 is unequally distributed on living room floors with smooth coverings, most likely because of displacement of dust from the middle towards the border due to activity. Expression as ng/g of dust and ng/m2 could not obviously be interchangeable.

House dust mite allergen in US beds: Results from the first national survey of lead and allergens in housing

Background: Although exposure to house dust mite allergen is a major risk factor for allergic sensitization and asthma, nationwide estimates of dust mite allergen levels in US homes have not been reported. Objective: The purpose of this study was to estimate the prevalence of dust mite allergen in beds of US homes and to identify predictors of dust mite allergen concentration. Methods: Data were obtained from the first National Survey of Lead and Allergens in Housing, a cross-sectional survey of 831 permanently occupied noninstitutional housing units that permitted resident children. Dust mite allergen concentration (Der f 1 plus Der p 1) was determined from a dust sample collected from a bed. The percentages of homes with concentrations at or greater than detection, 2.0 μg/g bed dust, and 10.0 μg/g bed dust were estimated. Independent predictors of allergen concentration were assessed with multivariable linear regression. Results: The percentages of US homes with dust mite allergen concentrations at or greater than detection, 2.0 μg/g, and 10.0 μg/g were 84.2% (SE, 1.73), 46.2% (SE, 2.0), and 24.2% (SE, 2.1), respectively. Independent predictors of higher levels were older homes, non-West census regions, single-family homes, no resident children, lower household income, heating sources other than forced air, musty or mildew odor, and higher bedroom humidity. Conclusion: Most US homes have detectable levels of dust mite allergen in a bed. Levels previously associated with allergic sensitization and asthma are common in US bedrooms. Predictors can be used to identify conditions under which homes are more likely to have increased dust mite allergen levels. (J Allergy Clin Immunol 2003;111:408-14.)

House dust mite allergen levels in carpeted sleeping accommodation are higher in private houses than public places.

To compare mite allergen levels in carpeted sleeping accommodation in private dwellings and public places. The concentration of Dermatophagoides pteronyssinus Group 1 allergen in house dust was measured in mat-tresses and bedroom floors in 12 homes, 5 hotels, 11 child care centres and a university hall of residence. Indoor temperature and relative humidity were also measured. A questionnaire clarified details regarding the age of the building, age of the carpet, method and frequency of cleaning, frequency of room use and use of air-conditioning. Median allergen levels in mattresses and carpets in private homes (21.1 and 20.6 micro g/g dust, respectively) were significantly higher than in public places (2.5 and 3.1 micro g/g, respectively; P < 0.0001). Mean relative humidity was significantly higher in private houses (68.5%; 95% CI 67.2-69.3%) than in public places (56.4%; 95% CI 52.7-60.1%; P < 0.0001). Carpeted sleeping accommodation in public places has lower house dust mite allergen levels than private houses. Lower levels of relative humidity may be an important component of the explanation.

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Dust mite allergens: ecology and distribution.

The most important allergy-causing mites found in homes worldwide are the house dust mites Dermatophagoides farinae, D. pteronyssinus, Euroglyphus maynei, and the storage mite Blomia tropicalis. Most homes contain multiple species. The most prevalent mite species and allergen in homes differ geographically, between homes within a geographical region, and among areas within a home. Therefore, it is important to know which mite species are present in a geographical area when performing diagnostic testing and prescribing immunotherapy. The key factor that influences mite survival and prevalence is relative humidity. Mites are present in homes in humid geographical areas and are rare or absent in drier climates unless humidity is artificially raised. Generally speaking, dust mite allergen levels are low in public buildings and transportation compared to levels in homes.

Allergens and endotoxin on mothers' mattresses and total immunoglobulin E in cord blood of neonates.

The current authors examined whether mite and cat allergen and bacterial endotoxin levels in dust of the mothers' mattresses were associated with cord blood immunoglobulin (Ig)E (CB-IgE) levels in newborns. Data from 1,332 term and normal weight neonates, from an ongoing birth cohort study, influences of life-style related factors on the immune system and the development of allergies in childhood (LISA), with complete information on exposure to biocontaminants in mattress dust and CB-IgE were analysed. Two thirds of CB-IgE were undetectable (<0.35 kU x L(-1)). Thus, 0.35 and 0.45 kU x L(-1) (4th quartile) were chosen as cut-offs. Nonparametric smoothing (generalised additive models) showed statistically significant confounder-adjusted associations between elevated CB-IgE levels (> or = 0.45 kU x L(-1)) and log-transformed exposures to cat (linear), mite (inverse u-shaped), and endotoxin (u-shaped). After adjustment for covariables, elevated CB-IgE levels (logistic regression using the 1st-4th quartiles of exposure) were positively associated with high cat-allergen exposure and medium exposure to mite allergen, but were inversely associated with exposure to endotoxin. The associations were similar, but somewhat weaker, when 0.35 kU x L(-1) was used as cut-off. These results, showing an association between prenatal allergen and endotoxin exposures and immunoglobulin E production, suggest that the development of foetal immune responses may be affected.

Exposure to dogs and cats in the first year of life and risk of allergic sensitization at 6 to 7 years of age.

Childhood asthma is strongly associated with allergic sensitization. Studies have suggested that animal exposure during infancy reduces subsequent allergic sensitization. To evaluate the relationship between dog and cat exposure in the first year of life and allergic sensitization at 6 to 7 years of age. Prospective birth cohort study of healthy, full-term infants enrolled in a health maintenance organization in suburban Detroit, Mich, who were born between April 15, 1987, and August 31, 1989, and followed up yearly to a mean age of 6.7 years. Of 835 children initially in the study at birth, 474 (57%) completed follow-up evaluations at age 6 to 7 years. Atopy, defined as any skin prick test positivity to 6 common aeroallergens (dust mites [Dermatophagoides farinae, D pteronyssinus], dog, cat, short ragweed [Ambrosia artemisiifolia], and blue grass [Poa pratensis]); seroatopy, defined as any positive allergen-specific IgE test result for the same 6 allergens or for Alternaria species. The prevalence of any skin prick test positivity (atopy) at age 6 to 7 years was 33.6% with no dog or cat exposure in the first year of life, 34.3% with exposure to 1 dog or cat, and 15.4% with exposure to 2 or more dogs or cats (P =.005). The prevalence of any positive allergen-specific IgE test result (seroatopy) was 38.5% with no dog or cat exposure, 41.2% with exposure to 1 dog or cat, and 17.9% with exposure to 2 or more dogs or cats (P =.003). After adjustment for cord serum IgE concentration, sex, older siblings, parental smoking, parental asthma, bedroom dust mite allergen levels at 2 years, and current dog and cat ownership, exposure to 2 or more dogs or cats in the first year of life was associated with a significantly lower risk of atopy (adjusted odds ratio, 0.23; 95% confidence interval, 0.09-0.60) and seroatopy (adjusted odds ratio, 0.33; 95% confidence interval, 0.13-0.83). Exposure to 2 or more dogs or cats in the first year of life may reduce subsequent risk of allergic sensitization to multiple allergens during childhood.

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.

Reduction of allergen by occlusive covering

. IN THE LAST decade, there has been increasing evidence of an association between levels of house dust mite (HDM) allergen, Der p 1, and asthma severity in sensitized asthmatics (1). Current advice is to cover all bedding items with HDMimpermeable covers, given that we spend approximately one-third of our lives in the bedroom (2). These measures are known to reduce bedding Der p 1 levels (3). However, little is known of the effect of these measures on airborne allergen. Sakaguchi and colleagues have developed a highly sensitive immunoassay for the quantification of HDM allergens in air samples, and demonstrated a five-fold reduction in airborne Der p 1 when used bedding (Japanese futons) was replaced by new bedding (4). Our aim was to study the effects of occlusive covering of bedding on airborne Der p 1 levels. Twelve adult subjects participated in the study, which was approved by the Wellington Central Ethics Committee. Before intervention, reservoirdust samples were individually obtained from mattresses, duvets and pillows as previously described (5) and air samples were collected in the bedrooms over seven consecutive nights (8 h/night at 1 l/min) with a personal air sampler (Shibata Scientific, Tokyo). Airborne particles were collected on fiberglass filters (25 mm diameter, Millipore, USA). Mattresses, duvets and pillows were then covered with occlusive covers (Alprotec, UK) for one week. During this time, air was sampled as describedaboveandreservoirdust samples collected directly from the bedding cover surfaces at the end of the study. The fiberglass filters were eluted overnight and Der p 1 was measured with a highly sensitive fluorometric immunoassay (detection limit 10 pg/ml) as previously described (4). Der p 1 in reservoir dust samples was measured by double-monoclonal antibody ELISA (6). Der p 1 values were log-transformed and results expressed as geometric means with 95% confidence intervals. Statistical analysis was by paired t-test (P,0.05 significant). Reductions in Der p 1 levels of approximately five-fold, 16-fold and 76fold, respectively, were found in pillows, duvets and mattresses after the one week intervention period, and airborne Der p 1 decreased by about six-fold .(Table 1). As airborne Der p 1 levels are in the picogram range, the ELISA technique (6) is not sensitive enough for aeroallergen quantification. Recently, Sakaguchi et al. developed a highly sensitive fluorometric ELISA method, able to quantify Der p 1 levels in the picogram range (7). With this method we have demonstrated an approximately six-fold reduction in airborne Der p 1 after one week of occlusive covering of the bedding. Sakaguchi and colleagues also showed about five-fold reductions in airborne Der p levels when used bedding was replacedwithnewbedding forfivedays (4). Interestingly, preand post-intervention HDM allergen levels were virtually identical in both studies (102 vs 102.1 pg/ m pre-intervention; 19.9 vs 17.5 pg/m post-intervention). Further studies are required to assess the role of individual bedding items to the contributionof aeroallergens, andwhether the modest reduction in airborne Der p 1 is accompanied by significant clinical improvement in house dust mite sensitized subjects. The study was supported by the Health Research Council of New Zealand.

アレルギー性鼻炎と住環境ダニ抗原量

Several reports indicate that the severity of perennial allergic rhinitis is related to levels of dust-mite allergens. In this study, the levels of dust-mite allergens measured in the homes of 13 people with allergic rhinitis and 10 healthy volunteers. Dust specimens were collected with a vacuum cleaner and analyzed for the presence of major mite allergens (Der 1=Der p1+Der f1, Der 2=Der p2+Der f2) by using ELISA. Levels of Der 1 were higher in bedclothes, in bedrooms, and on family room floors. There were no differences between the homes of the 13 people with allergic rhinitis and the 10 healthy volunteers. No association was found between levels of dust-mite allergens and the severity of nasal symptoms. Although the levels of mite allergens increased in most of homes 2 months after cleaning, there was an insignificant tendency for improvement in nasal symptoms in homes with decreased levels 2 months after cleaning.

Environmental Allergens and Irritants in Schools: A Focus on Asthma

As part of the Partners in School Asthma Management Program, environmental data were collected from 385 rooms in 60 elementary schools in southeast Texas, using an Environmental Observation Checklist and a Q-TRAK Indoor Air Quality Monitor. Dust samples for allergen analysis were collected from floors, carpets, and area rugs in 80 classrooms in a subset of 20 schools. CO2 levels > 1,000 ppm were found in 86% of rooms; 69% had indoor humidity above recommended levels. Der p I dust mite allergen levels > 2,000 ng/g were present in 20% of rooms, but only 2.5% of rooms had Der f I mite allergen levels exceeding recommended tolerances. Detectable levels of cockroach allergen (Bla g II) were found in all schools (median 5.5 ng/g), with 10% of rooms over the recommended threshold. Almost two-thirds of classrooms had mold spore counts > 10,000 col/g (median, 14,400 col/g; range, 2,000-52,000 col/g).

House dust mite allergen levels in German day-care centers

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

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Effects of Physical Interventions on House Dust Mite Allergen Levels in Carpet, Bed, and Upholstery Dust in Low-Income, Urban Homes

House dust mite allergen exposure is a postulated risk factor for allergic sensitization, asthma development, and asthma morbidity; however, practical and effective methods to mitigate these allergens from low-income, urban home environments remain elusive. The purpose of this study was to assess the feasibility and effectiveness of physical interventions to mitigate house dust mite allergens in this setting. Homes with high levels of house dust mite allergen (Der f 1 + Der p 1 &gt; or = 10 microg/g dust by enzyme-linked immunosorbent assay) in the bed, bedroom carpet, and/or upholstered furniture were enrolled in the study. Carpets and upholstered furniture were subjected to a single treatment of either dry steam cleaning plus vacuuming (carpet only) or intensive vacuuming alone. Bed interventions consisted of complete encasement of the mattress, box spring, and pillows plus either weekly professional or in-home laundering of nonencased bedding. Dust samples were collected at baseline and again at 3 days (carpet and upholstery only) and 2, 4, and 8 weeks posttreatment. We compared pretreatment mean allergen concentrations and loads to posttreatment values and performed between-group analyses after adjusting for differences in the pretreatment means. Both dry steam cleaning plus vacuuming and vacuuming alone resulted in a significant reduction in carpet house dust mite allergen concentration and load (p &lt; 0.05). Levels approached pretreatment values by 4 weeks posttreatment in the intensive vacuuming group, whereas steam cleaning plus vacuuming effected a decrease that persisted for up to 8 weeks. Significant decreases in bed house dust mite allergen concentration and load were obtained in response to encasement and either professional or in-home laundering (p &lt; 0.001). Between-group analysis revealed significantly less postintervention house dust mite allergen load in professionally laundered compared to home-laundered beds (p &lt; 0.05). Intensive vacuuming and dry steam cleaning both caused a significant reduction in allergen concentration and load in upholstered furniture samples (p &lt; 0.005). Based on these data, we conclude that physical interventions offer practical, effective means of reducing house dust mite allergen levels in low-income, urban home environments.

Allergenic materials in the house dust of allergy clinic patients.

Environmental agents including animal, fungal, tree, and weed antigens are known to cause allergic rhinitis and asthma. The following study was performed to measure the antigen concentration of several of these in house dust of children seen in an allergy clinic. Comparisons are made between household allergen levels of children seen for asthma and children seen for other reasons. Dust samples were solicited from patients in a pediatric allergy specialty clinic and other individuals associated with the clinic. Persons submitting dust were asked to complete a questionnaire describing their house. Samples were extracted, centrifuged, and filtered for sterility. Samples were stored in 50% glycerol at -20 degrees C. Specific antigens for Alternaria, Cladosporium, Aspergillus, Candida, Dermatophagoides farinae, cat, dog, oak, fescue, ragweed, plantain, and cockroach were measured using inhibition assays developed with whole antigen extract. Allergens Der p1, Der f 1, Alt a 1, and Alt a 70 kD were measured using double monoclonal antibody assays. Significant concentrations of whole antigen from cat, dog, oak, Alternaria, and Cladosporium were detected. Between 0.1 and 18 microg of Der f1 and Der p1 per gram of dust were also measured. Alt a 1 and Alt a 70 kD levels varied between 3.0 and 1000 U/g of dust. Significant positive correlations were observed in levels of dust mite and Alternaria allergen for patients with an evaluation of asthma. We found measurable levels of fungal antigens (Alternaria, Cladosporium), mite antigens, and animal antigens (dog and cat) in the majority of dust samples in this self-selected set of allergy clinic patients. Specific allergens Alt a 1, Alt a 70kD, and Der p 1 were significantly higher in the homes of asthmatic patients when compared with patients seen for reasons other than asthma. These studies support the hypothesis that fungal allergen exposure is an important component in the pathogenesis of the clinical condition known as asthma.

Exposure to cockroach allergen in the home is associated with incident doctor-diagnosed asthma and recurrent wheezing

Background: Indoor inhaled allergens have been repeatedly demonstrated to worsen asthma in sensitized individuals, but their role in incident asthma is more controversial. Objective: We investigated the relationship between exposure to allergens (dust mite, cat, and cockroach) measured in the home and incident doctor-diagnosed asthma and recurrent wheezing in children born to parents with asthma, allergies, or both. Methods: From an ongoing longitudinal family and birth cohort study, we identified 222 siblings (median age, 2.87 years) of the index children. Allergen levels in the home were measured from dust samples obtained at the beginning of the study. Incident doctor-diagnosed asthma and recurrent wheezing were determined from questionnaires administered at 14 months and 22 months after the initial questionnaire. Results: Thirteen (5.9%) children were reported to have incident asthma, twenty (9.0%) children had recurrent asthmatic wheezing, and 18 (8.1%) had recurrent wheezing without asthma. Compared with children living in homes with Bla g 1 or 2 levels of less than 0.05 U/g, children exposed to Bla g 1 or 2 levels of 0.05 to less than 2 U/g had a relative risk for incident asthma of 8.27 (95% confidence interval, 1.04-66.04), whereas children exposed to Bla g 1 or 2 levels of 2 U/g or greater had a relative risk for incident asthma of 35.87 (95% confidence interval, 4.49-286.62). Cockroach allergen exposure was likewise a significant predictor for recurrent asthmatic wheezing. Neither dust mite nor cat allergen levels were significantly associated with either outcome. These findings remained after control for several covariates. Conclusion: Exposure to cockroach allergen early in life may contribute to the development of asthma in susceptible children. (J Allergy Clin Immunol 2001;107:41-7.)

(1-->3)-beta-D-glucan and endotoxin in house dust and peak flow variability in children.

House dust-associated bacterial endotoxins have been shown to be associated with asthma severity, and a similar role has been suggested for fungal (1-->3)-beta-D-glucans. In this study the relation between these agents and peak expiratory flow (PEF) variability was investigated in 148 children 7 to 11 yr of age of whom 50% had self- or parent-reported chronic respiratory symptoms. All children self-monitored twice daily their PEF for a period of 16 wk. Dust samples were collected from mattresses and from living room and bedroom floors, and endotoxin and (1-->3)-beta-D-glucan were measured in dust extracts. The relations with mean daily PEF variability (Ampl%mean) were investigated by linear regression analysis, adjusting for dust mite allergen levels, presence of pets, and type of floor cover. In unadjusted analyses the levels of both endotoxin and (1--> 3)-beta-D-glucan per square meter of living room floor were significantly associated with PEF-variability (but not when expressed per gram of sampled dust), particularly in atopic children with asthma symptoms. Adjusted analyses showed the same association for (1--> 3)-beta-D-glucan but not for endotoxin. Although no associations were found with microbial agent levels in bedroom floor or mattress dust, high levels of (1-->3)-beta-D-glucan in living room floor dust apparently increase PEF variability in asthmatic children.

Association of asthma symptoms and severity with indoor bioaerosols.

In this study, repeated measurements were made of levels of mold spores, bacteria, and dust-mite allergens over a 7-month period in the homes of asthmatics, and relationships with measures of asthma severity were evaluated. A sample of 57 asthmatic individuals, living in 44 homes in East Moline, Illinois, and nearby communities, participated in a panel study. The homes were visited up to nine times during the study to collect air and dust samples. Asthma severity indicators were derived from questionnaire data and from the daily health records from the panel study. Associations between indoor levels of mold spores, bacteria, and dust-mite allergens were tested with several asthma severity indicators. There was evidence of associations between all asthma severity measures and levels of total and gram-negative bacteria, but mold-spore abundance was associated only with emergency room (ER) visits for asthma. No significant associations were found with house-dust-mite allergen and any of the asthma severity indicators, but the levels of dust-mite allergen were low, with median concentrations of 0.18 microg/g dust Der f 1 and 0.19 microg/g dust Der p 1. Some evidence was found for associations of increased concentrations of gram-negative bacteria and mold spores with asthma severity, particularly with ER visits. No association was found between house-dust-mite allergen and asthma severity indicators; however, the mite-allergen levels in the study homes were generally well below the proposed threshold level of 2 microg/g dust.