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

Abstract

To characterize seasonal variation of three allergens (dust mite, cat, and cockroach) and total culturable fungi and to explore whether residential characteristics were associated with the concentrations of these agents, floor dust was collected from 47 inner-city homes in Minneapolis, Minnesota, over a 1-year period. A longitudinal analysis of allergen and fungal concentrations was carried out using mixed-effect models. Overall, relative humidity was a better predictor of allergen concentrations over time than indoor temperature. Seasonal variation of cat and cockroach allergens was negligible compared with the variability associated with residential characteristics such as race/ethnicity, family income, and the presence of cats. Fungal concentrations showed significant seasonal variation that outweighed the variability associated with residential characteristics. Less than 30% of the dust mite allergen and cockroach allergens concentrations were above limits of detection. Observed cockroach allergen concentrations were higher in Spanish- and Somali-speaking households than in English-speaking households, while English-speaking households had significantly higher cat allergen concentrations compared with the other language groups. The ratios of within-home to between-home variance for total culturable fungi, dust mite, cockroach, and cat allergen concentrations were 2.54, 1.91, 0.55, and 0.24, respectively. This ratio is used to predict the number of repeated measurements of each allergen required to robustly estimate long-term exposure estimates such that exposure misclassification bias is kept within acceptable limits. It is not clear whether repeated measurements of dust mite and cockroach allergens are required for long-term average exposure because of the large fraction of nondetects. It is concluded that a single measurement of cat allergen is a reasonable surrogate for long-term average exposure, since repeated measurements over time were highly correlated. Total culturable fungi will require greater than nine repeated measurements for robust assessment of long-term exposures because of low correlations in fungal measures over time.

Seasonal Variability of Culturable Fungal Genera in the House Dust of Inner-City Residences

“…(24,46) In our previous work, we evaluated the effects of seasonal variability and household characteristics on total fungal concentrations in house dust. (43) We found significant seasonal variability in total culturable fungal concentrations, and that within-home variability was much larger than between-home variability. The aim of this analysis was to characterize seasonal variability of individual fungal genera, explore this observed variability in light of the current evidence linking health effects to individual genera, and discuss the implications of these findings for fungal exposure assessment in health studies.…”

“…HARS was conducted in a diverse population of low income households over a 1-year period in south Minneapolis, Minnesota, and the study design and population are described elsewhere and key features briefly summarized here. (43,47) During the study period, a total of six home visits were completed approximately every 2 months.…”

“…(9,10,33,41) Studies exploring this issue indicate that the variation of culturable total fungal concentrations over time is larger within homes than between homes. (42,43) There are relatively few studies exploring longitudinal variability of culturable fungi at the genus or species level. (44,45) Studies conducted in the Netherlands indicate that fungal species isolated from house dust samples varied substantially in two repeated measurements over a 6-week period, (44) and that the frequency of occurrence of fungal genera appeared to vary by sampling season (though a statistical analysis was not performed).…”

Allergen levels in inner city homes: baseline concentrations and evaluation of intervention effectiveness

“…This result may be partially attributed to considerably higher baseline levels in single family homes compared to apartments, although this observed difference does not appear to be an artifact and likely reflects reality in these environments. Nevertheless, 55% of study samples had fungal levels above the health-based threshold, with clear seasonal variability (Cho et al, 2007). Analysis of pre-versus post-intervention samples indicated that the cleaning intervention modestly reduced the percentage of samples above the threshold, from 44% to 35%.…”

“…This was a longitudinal study designed to (1) evaluate the variability in allergen levels over time (Cho et al, 2007), and (2) quantify the individual and joint effects of the education-only and cleaning-only interventions on household allergen levels. As shown in Figure 1, each residence in the study was visited up to six times over a year, and all homes eventually received both the education and cleaning interventions on a randomized basis.…”