Our principal goal was to determine if there was any relationship between building characteristics and measured indoor allergens, since this has not been previously reported. While our study comprised lower levels of cat and dust allergens and higher levels of cockroach and mouse allergens compared to national studies, our allergen levels were comparable to other New York City studies examining indoor allergens.9,54
Our levels are likely less comparable to national data, because these data are generally less representative of the urban context; for example, they contain few high-rise buildings.10,51,77,85
From this examination, we begin to understand how building-level characteristics may be related to allergen levels. We did not find associations between building-level characteristics and Der f 1 or Fel d 1 allergen in bivariate or fully adjusted linear models. In previous studies, a relationship has been found between older homes and single family homes as independent predictors of higher levels of dust mite allergens.85
To examine this, we dichotomized building age to explore the relationship with older homes (pre-1945 and post-1945 construction), but we did not see a relationship (data not shown). This may be the result of small sample size or very low levels of dust mite allergen within our study sample. Although, when we examined a cutpoint by using the detection limits of Der f 1, we observed an association between Der f 1 and the household-reported presence of rodents. There is little literature to guide us on this finding. One possible explanation for the observed association may concern the presence of water: rodents are attracted to water, and water produces more humidity, which is related to dust mites. However, it may be in this instance that the household-reported presence of rodents is a proxy for some other factor (water or something else) not controlled for in “fully adjusted” analyses.
Concerning cat allergen, we stratified by cat ownership to further elucidate the relationship between building-level characteristics in homes that might have higher levels of cat allergen because of the presence of a cat. Yet, there were no further relationships found upon stratification among cat owners. Results of the National Survey of Lead and Allergens in Housing noted that essentially all USA homes contain Fel d 1 (whether the home actually contains a cat or not), and that the majority of these homes had levels that exceeded the proposed cutpoint for sensitization to these allergens.77
While the majority of the literature just discusses whether or not a cat is present, a 2007 abstract by Panjwani and colleagues does discuss the existence of Fel d 1 in homes where “cat non-owners” reside.86
Concerning cutpoint effects for Fel d 1 observed at the limits of detection, we found a strong association with high-rise apartment buildings and a slight association with the age of the building. Using the clinically relevant cutpoint, there seems to be an increased risk for the presence of cat allergen (>1 U/g) in a high-rise apartment building compared to a house/duplex (OR, 6.29; 95% CI, 1.51, 26.21).
For Bla g 2 and MUP allergen levels, building-level characteristics were associated in bivariate and fully adjusted linear models. In these models, cockroach allergen was statistically significantly associated with the household-reported presence of cockroaches and living in public housing. Previous research by Chew et al. supports this finding with which our results are consistent; they reported that seeing cockroaches and living in public housing in New York City are both highly associated with the existence of cockroach allergen.54
Interestingly, in our study, building size, specifically living in a high-rise apartment vs. a house/duplex, was statistically significant in the bivariate model, but not in the fully adjusted linear model. When building size alone was removed from the fully adjusted model, both the presence of cockroaches reported by household and living in public housing remained statistically significant, and the ratios were stronger. Therefore, removing building size from the model increased the effect of these predictors, suggesting that building size is important for understanding levels of cockroach allergen. This may be linked to the transport and staying power of allergens and pests in, as well as to the condition of, different size buildings, especially in urban areas. Just as in linear regression analyses, the relationship between Bla g 2 at a clinically relevant level of >1 U/g and the household-reported presence of cockroaches was statistically significantly associated in logistic regression analyses. That is, Bla g 2 seems to be related to a household report of the presence of cockroaches in/of the same unit from which the Bla g 2 sample was taken. These results are consistent with prior literature.25,58
The household-reported presence of rodents and building size were positively statistically significantly associated with MUP allergen in bivariate and fully adjusted linear models. The household-reported presence of rodents, living in public housing, and building size were statistically significantly associated with MUP allergen at a clinically relevant level of >1.6 μg/g. Whether modeled continuously or at a clinically relevant cutpoint (>1.6 μg/g), there is an evident relationship between the household-reported presence of rodents and mouse allergen. That is, the presence of MUP seems to be related to a household report of rodents in/of the same unit from which the MUP sample was taken. This finding is consistent with previous literature.9,54
There is also a relationship between mouse allergen and building size, which becomes stronger when a clinically relevant cutpoint is employed (>1.6 μg/g). However, the relationship between building size and mouse allergen turns out to be a complex association. While our results indicated that living in a multistory building is associated with a decrease in the existence of mouse allergen, Chew et al. and Cohn et al. suggested that higher levels of mouse allergen were associated with living in multistory buildings, low-rise buildings (<8 floors)9
and high-rise apartments (≥5 floors),10
However, previous work by Bradman et al. and Berg et al. reported results similar to ours: an association between higher levels of mouse allergen and detached housing.62,63
When we dichotomized building size as the relationship between living in a house/duplex (vs. living in a multistory), this suggested a 69% (1.69; 95% CI, 1.18, 2.41) increase in the existence of mouse allergen (data not shown). Bradman et al. hypothesized that detached homes provided more points of easy entry on the ground floors.62
In addition, we might hypothesize that other neighborhood-level factors, such as proximity to restaurants or grocery stores, or large-scale urban planning projects, could influence the amount of infestation. Area-level predictors may be an especially interesting characteristic to explore in terms of mouse allergen; such that an issue like housing dilapidation at the neighborhood-level could play an important role in explaining this phenomenon. The question is, why do some types of housing have different or higher rates of allergens than others? Here, houses/duplexes seem to have more mouse allergen among a sample of mainly Puerto Ricans in the Bronx. Lastly, we found that those living in public housing are at an increased risk of being exposed to clinically relevant levels of mouse allergen (>1.6 μg/g; OR, 6.20; 95% CI, 1.01, 37.95). However, studies in NYC and Boston have found low levels of mouse allergen in public housing.54,58
This study has limitations. Firstly, the sample size of this prospective birth cohort at baseline was small (N
261). Concerning cutpoint examinations (logistic regression analyses), some wide confidence intervals are present, although the findings are statistically significant. Secondly, this sample was limited to a cohort of Puerto Rican participants, all with a history of mother-reported inhalant allergy or asthma. While such a cohort might help elucidate the relationships under study within this population, we cannot generalize beyond this small, relatively homogeneous group. Next, the season in which allergen samples were taken is not available. Lastly, many building-level exposures were also proxy variables (e.g., household-reported pest presence) while still other relevant variables were unavailable (e.g. number of building violations related to pests).
This work helped to more clearly examine allergens in relation to building characteristics; a level not yet fully explored. In particular, we focused on ways to measure physical places at the building level since it is evident that structural issues need to be considered in order to reduce health disparities. Building issues in urban spaces are often controlled by landlords, city codes, and urban developers, and therefore understanding the influences of the structural building on allergen levels may help locate responsibility in spheres still considered unrelated to the prevention of asthma.87
Future studies should incorporate a city-wide, or nationally, representative sample of USA participants to further clarify the relationship between building characteristics and indoor allergens. While a focus on Puerto Ricans is warranted due to the high asthma burden in this population, a representative sample will provide us with a better idea of the relationship between building-level factors and asthma morbidity in the general population. Likewise, a longitudinal study would be important to capture exposures across the life span, beginning during the prenatal period and following the cohort forward. This would help us to determine at what period building exposures may be important for allergic sensitization and asthma development/morbidity.
In addition, future studies concerning the building level might aim to collect data on building characteristic variables that might more precisely capture issues of interest. The data as we might ideally like to have it is not currently available. In the future, we might want to ask participants, for example, about pest presence in other areas in and around the building; allergen measurements could be taken in these spaces outside of the household unit. In addition, odor, heating, and ventilation systems could be assessed, as suggested by previous studies.4,48,49,52
Furthermore, a well-powered future study might statistically account for the fundamental multilevel nature of this work, examining participants, buildings, neighborhoods, and regional issues.49,88
Altogether, substantial further research remains to be done, but this study, and the work that precedes it, demonstrated that the association between building characteristics and asthma morbidity merits attention. The continuing asthma epidemic suggests that household physical triggers alone do not paint a complete picture. We will have to seek a broader understanding of what influences asthma morbidity and mortality—and shape policies on multiple levels of influence and across the life span.