Variability of house dust mite allergen exposure in dwellings.

Abstract

Tlhe variability of repeated house dust mite (HDM) allergen determinations at the same site within 3-24 months was evaluated on previously collected samples. Between two and four repeated measurements of Der p 1, a major allergen of Dermatophagoidespteronyssinus and Der f 1, a major allergen of D. farinae, on 46 carpets and 31 mattresses were analyzed. In 90% of carpets and mattresses, HDM allergen concentrations were cinically relevant (at least one measurement >0.1 pg Der p 1 + Der f l/g dust). The coefficients ofvariation (CVs) for allergen concentrations in repeated samples over time (55.3-82.0% for the two allergens in beds and carpets) were clearly greater than the CVs for multiple samples collected at the same time (4.0-32.6%). Determination ofallergen mass per square meter of surface instead of concentration per gram of dust resulted in an even greater There are some other considerations of practical relevance that have not been addressed so far. First, the Australian study measured variability in 2-week intervals. This design might fail to detect long-term variations of exposure. Second, the allergen concentration in sampled dust might be massively "diluted" with allergen-free dirt from outside. Is the total sampled mass of allergen a measure of less variability? Finally, can the reliability be improved if sampling is always done by the same trained field worker rather than by residents following written instructions?Answers to these questions should help improve methods of future field studies of HDM allergen exposure. For this purpose it is also useful to estimate how many samples are needed to compensate for the variability caused by influences that cannot easily be controlled by study design. Methods Study DesignVariability ofsampling and dust extraction procedures. To describe the real variability of HDM exposure, it is necessary to assess the impact of laboratory procedures on total variability. Besides the variability of the assay itself (interassay and intra-assay variability; see "Laboratory Analysis") the influence of our sampling and dust extraction procedures on the variability of results was examined in a methodical study.Sample pairs from six mattresses (both longitudinal halves) and six carpets (two squares of 1 m2) were collected at the same time. To evaluate the variability of the extraction procedure, each of these two samples and two additional single samples from two mattresses (n = 26) were divided into two to nine dust portions. These portions were analyzed separately, and the mean and the coefficient of variation (CV) were calculated for each set of portions. The mean was interpreted as the value of the whole original sample. The values of the two original samples collected at one site were then used to calculate CVs for sampling at the same site at the same time.Long-term variability ofallergen concentration at the same site. We retrospectively analyzed dust samples from two field studies in which HDM allergen exposure was determined repeatedly (within 3-24 months).

Determination of mite Allergens in House Dust Using the Enzyme Immunoassay

“…These results show that Der p 1 and Der f 1 levels in carpet dust samples were generally low and are in accordance with our earlier study on urban Zagreb homes (Der p 1 and Der f 1 median <1 µg g -1 ) which used the Dustscreen TM test (8). The ranges of Der p 1 and Der f 1 were (0.1-12.5) µg g -1 and (0.1-31.2) µg g -1 , respectively, confirming similarly large ranges from earlier studies (8,(11)(12)(13)20) for both allergens. In this study, dust mass fraction of Der p 1 and Der f 1 varied by an order of 10 2 between homes (Table 1).…”

“…Currently, this method provides the best index of allergen exposure in the settled dust (20). So far, ELISA has not taken root in Croatian laboratories for measuring mite allergen.…”

Feasibility of Using Subject-Collected Dust Samples in Epidemiologic and Clinical Studies of Indoor Allergens

“…Pearson’s correlation coefficients for concentrations of Fel d 1 and Der p 1, respectively, were 0.76 and 0.67 for the bed and 0.82 and 0.58 for the floor (Wickens et al 2004). Other studies have indicated that allergen concentrations vary between pairs of side-by-side bed and floor samples (Hirsch et al 1998; Marks et al 1995). This variation is due to random error, variation in laboratory assays, and the heterogeneity of allergen concentrations across surfaces.…”

Longitudinal Evaluation of Allergen and Culturable Fungal Concentrations in Inner-City Households

“…While dust mite allergens may vary by geographic location and season, (17,19,22−27,46−49) the large fraction of nondetects may explain why the authors did not observe high, season-adjusted within-home correlations for Der f 1 and Der p 1 observed in other studies. (23,30,32) The authors imputed missing values with half the MQL, thereby reducing between-and withinhome variability. They performed a sensitivity analysis using 100% MQL, 10% MQL, 1% MQL and a combination of 100% MQL and 1% MQL for longitudinal analyses.…”

“…In contrast, Hirsch et al (30) concluded that repeated measurements were recommended for Der p 1 and Der f 1 even though within-home variance of these agents was much smaller than between-home variance. Giovannangelo et al (31) reported that within-home variance of Der p 1 and Fel d 1 was smaller than between-home variance, but for Der f 1, larger within-home variance was observed.…”