Are Building-Level Characteristics Associated with Indoor Allergens in the Household?

Abstract

Building-level characteristics are structural factors largely beyond the control of those who live in them. We explored whether building-level characteristics and indoor allergens in the household are related. We examined the relationship between building-level characteristics and indoor allergens: dust mite, cat, cockroach, and mouse. Building-level characteristics measured were presence of pests (seeing cockroaches and rodents), building type (public housing, buildings zoned commercially and residentially, and building size), and building condition (building age and violations). Allergen cutpoints were used for categorical analyses and defined as follows: dust mite: >0.25 μg/g; cat: >1 μg/g; cockroach: >1 U/g; mouse: >1.6 μg/g. In fully adjusted linear analyses, neither dust mite nor cat allergen were statistically significantly associated with any building-level characteristics. Cockroach allergen was associated with the presence of cockroaches (2.07; 95% CI, 1.23, 3.49) and living in public housing (2.14; 95% CI, 1.07, 4.31). Mouse allergen was associated with the presence of rodents (1.70; 95% CI, 1.29, 2.23), and building size: living in a low-rise (<8 floors; 0.60; 95% CI, 0.42, 0.87) or high-rise (8 + floors; 0.50; 95% CI, 0.29, 0.88; compared with house/duplex). In fully adjusted logistic analyses, cat allergen was statistically significantly associated with living in a high-rise (6.29; 95% CI, 1.51, 26.21; compared with a house/duplex). Mouse allergen was associated with living in public housing (6.20; 95% CI, 1.01, 37.95) and building size: living in a low-rise (0.16; 95% CI, 0.05, 0.52) or high-rise (0.06; 95% CI, 0.01, 0.50; compared with a house/duplex). Issues concerning building size and public housing may be particularly critical factors in reducing asthma morbidity. We suggest that future research explore the possible improvement of these factors through changes to building code and violations adherence, design standards, and incentives for landlords.

Introduction

The relationships between both individual and household characteristics and indoor allergens in the household are well known.^1–3 Yet, there are gaps in our understanding of the relationship between building-level characteristics and allergens. Previous literature has demonstrated a relationship between building materials and associated chemical or biological agents (e.g., volatile organic compounds and fungi) and building-related symptoms/illness,^4–7 supporting the idea that building characteristics are related to health symptoms. In addition, housing type and building age have been examined.^8–11 We explored the relationship between a set of building-level characteristics (presence of pests, building type, and building condition) and common urban indoor allergens (dust mite [Der f 1], cat [Fel d 1], cockroach [Bla g 2], and mouse urinary protein [MUP]) in a cohort of Puerto Rican residents in New York City.

Asthma and Indoor Allergens

Asthma, affecting millions of Americans, is a critical and potentially fatal lung disease.¹² It is associated with physical, social, and environmental issues.^13–22 Over the past two decades, asthma morbidity and mortality within the USA have increased to epidemic proportions among all age, race, and gender groups in every region of the country.²³

High levels of indoor allergens are associated with asthma morbidity.^11,24–26 Asthma and sensitization to cockroach allergen are widely known to be associated.^27–29 High exposure to cockroach allergen is a risk factor for both asthma medication use and asthma-related hospitalizations.²⁶ In addition, the presence of dust mite, cat, cockroach, and mouse allergen in the home have been found to be related to airway hyperresponsivesness³⁰ and sensitization to dust mite and cat allergen are related to wheezing.³¹ Mouse allergen’s contribution to asthma has also been studied,^9,32–35 and significantly more asthmatic children have been shown to be allergic to mice (assessed by skin prick) when mouse allergen levels reach a certain cutpoint.³⁶ In all, increased exposure to allergens, particularly dust mites and cockroaches, is related to an increased risk for the development of asthma.^37–39

Building Level

While researchers have established that asthma is an ever-growing burden, more so for some USA communities than others, they have not yet firmly delineated the issues that put people at highest risk for being exposed to indoor allergens, and/or developing asthma. Most asthma research in the USA focuses on in-unit and other individual-level triggers, with a few exceptions.^40,41 Such triggers include household environmental exposures, high parental stress, poor medication adherence, child behavioral or emotional concerns, and poor medical care.^{3,16,21,22,24–26,42–47}

An emerging literature does suggest that indoor allergens associated with asthma are related to the buildings in which people live.^{10,11,48–52} Considerable literature firmly establishes that the presence of cockroaches and rodents (i.e., pests) is associated with higher levels of asthma morbidity.^{5,10,24,51,53–57} Likewise, recent literature has highlighted the relationship between asthma morbidity and building types such as public housing;^54,58 mixed-use buildings, i.e., property containing both residential and commercial space;^59–61 and building size.^9–11,62,63 Lastly, indoor allergens and asthma morbidity have also been linked to building conditions; in particular older buildings and building violations in or near the residential building have been associated.^{8,10,48,49,51,52} However, little explicit examination by building type and condition has occurred, especially in the USA.

We explored the relationship between building characteristics and indoor allergens in the Puerto Rican Asthma Project cohort.⁶⁴ Puerto Ricans are among the racial/ethnic groups most widely affected by asthma in the USA.^24,65–74 We hypothesized that specific building-level characteristics—presence of pests and building type and conditions—were associated with levels of indoor allergens.

Methods

The Puerto Rican Asthma Project (PRAP) is a prospective birth cohort of Puerto Rican children born in New York City (NYC) to mothers who had asthma and/or inhalant allergy. Full study details have been discussed previously.⁶⁴ Briefly, 274 mothers and their newborns completed the initial baseline home visit within a few weeks after the birth of the child. Participant mothers answered questions on behalf of their household and child in either Spanish or English. A team of two technicians, one of whom was bilingual (Spanish/English), collected dust samples and administered a questionnaire to the mother. During this baseline visit, the surface of the mother’s bed was vacuumed for 3 minutes and samples were analyzed for Der f 1, Bla g 2, Fel d 1, and MUP allergens as previously described.⁶⁴

Building characteristics data were collected from the New York City Open Accessible Space Information System Cooperative (OASIS) database (www.oasisnyc.net) from March to April 2007.⁷⁵ OASIS is a web-based Geographic Information Systems mapping resource for NYC. It is a partnership of more than 30 federal, state, and local agencies, private companies, academic institutions, and nonprofit organizations, creating a one-stop, interactive mapping and data analysis application via the Internet. Each participant address was entered into the OASIS mapping system a minimum of three different times to collect building characteristics data. If the address still could not be located, the participant was dropped from the analysis. All study participant addresses were geocoded by the commercial geocoding firm Mapping Analytics.⁷⁶ At baseline, 12 participants were excluded from the building-related statistical analysis because they were not available in OASIS. Eight lived outside the five NYC boroughs and four addresses could not be located in OASIS. Thus, at baseline, 261 participants remained for analysis. The Human Subjects Committees at the Harvard School of Public Health and at Columbia University Medical Center approved this study.

Measures

PRAP outcome, pest, and sociodemographic data were collected from September 2002 to August 2005.

Allergen Outcome Measures We examined four indoor allergens as independent outcomes of building-level characteristics, including Der f 1, Fel d 1, Bla g 2, and MUP. Samples were collected from mothers’ beds. Allergen levels were ln-transformed to approximate normality. Logistic regression was also used to explore previously published allergen level thresholds for allergic sensitization, when possible (cockroach, >1 U/g [1 unit = 40 ng] and mouse, >1.6 μg/g); and if this was not possible, the detection limits of the relevant immunoassay were used (dust mite, >0.25 μg/g; cat, >1 μg/g).^{9,26,28,37,77,78}

Building Exposure Measures Presence of pests (e.g., cockroaches and rodents) was reported by mothers on the baseline interview survey. Building type was assessed by research staff and characterized as duplex, house, or multistory, with a follow-up question to the resident about the total number of floors. For this analysis, building type was categorized as follows: house/duplex, low-rise apartment (<8 floors), and high-rise apartment (8+ floors).We measured building type and condition data for each participant’s baseline address from information gathered from the OASIS database. Building-level data were collected from the OASIS database (www.oasisnyc.net) from March to April 2007 using participants’ addresses.⁷⁵ We collected building-level data on public housing and commercial/residential zoning to determine building type and data on building age and building violations cited as Environmental Control Board (ECB) violations to determine building condition. Each participant’s address was characterized as public housing or not public housing, and being either a purely residential building or a building with both commercial and residential properties. Building age was calculated by subtracting the year the building was built from the year data were collected. Addresses for all study participants were geocoded by the commercial geocoding firm Mapping Analytics.⁷⁹ Building violations for each address were collected by linking to the NYC Department of Buildings (DOB) Property Profile Overview to obtain the number and type of violation for each address.⁸⁰ An ECB violation is a notice that a property does not comply with a provision of the NYC Building Code and/or NYC Zoning Resolution, and such violations are resolved at the Environmental Control Board, an administrative law court where a violator must (a) pay a civil penalty and correct the violating condition and (b) file a Certificate of Correction with the DOB.⁸¹ Violations were standardized by building age and number of units in the building, and then multiplied by 100 for ease of interpretability. The OASIS database and the NYC Department of Buildings, Property Profile Overview are publicly available data repositories.

Covariates Mother’s education and household income were measured in the baseline interview survey and were dichotomized: education (≤high school graduate (referent) or ≥some college); household income (≤$39,999 (referent) or ≥$40,000+).

Sociodemographic Variables During the baseline interview survey, information was collected about marital status (married, divorced, separated, widowed, never been married), birth place (Mainland USA, Puerto Rico, Dominican Republic, Mexico, Other), and how long they had lived in the USA (number of years).

Analysis

We evaluated the association (p < 0.05) between building exposures and household indoor allergen levels, using bivariate and multivariable linear regression as well as logistic regression for allergen cutpoint levels, as specified earlier. Possible confounders (income and education) were included in all subsequent analyses.

We first examined the distributions of sociodemographic variables, potential confounders (income and education), building exposures, and the outcomes of interest (indoor allergens). The natural log was used for modeling allergens, as well as reporting the geometric mean.^33,82 We then evaluated the association between building exposures and indoor allergens, using bivariate and multivariable linear and logistic regression (p < 0.05). Possible confounders (income and education) determined to be related to building exposures and outcomes a priori were maintained in all subsequent multivariable analyses. Bivariate models examined the relationship of one building exposure at a time to each outcome. The first set of multivariable models examined the same relationships, while also adjusting for income and education. The next set of multivariable analyses examined fully adjusted linear models, where each parameter estimate is adjusted for all other exposures in the model, including income and education. The next set of multivariable analyses examined fully adjusted logistic models, where each parameter estimate is adjusted for all other exposures in the model, including income and education. For multivariable linear analyses, all ratios and 95% confidence intervals were back-transformed to represent the original allergen scales instead of log scales. All analyses were performed in SAS 9.1 and JMP 7.0.^83,84

Results

Sample Most mothers in the sample have never been married (64.8%) and were born on the Mainland USA (73.6%). One fifth (20.7%) were born in Puerto Rico. In addition, 56.3% of mothers had a high school education or less, and 80.8% lived in households where the combined family income was less than $39,999/year.About 15% of the participants lived in public housing, and 16.9% lived in a building zoned both commercially and residentially. About 59% lived in low-rise apartment buildings, and 17.8% lived in high-rise apartment buildings (referent = duplex/house). The average age of buildings where participants lived was 68.9 years. The average number of standardized ECB violations per unit was 0.2. (Table 1) Mothers reported seeing cockroaches (74.3%) and rodents (42.9%) in their homes in the past 4 months (household-reported sightings). Baseline median and geometric mean allergen levels in participants’ homes (bedroom dust sample) are listed in Table 2.

Table 1.

Demographic and building-level characteristics at baseline (n = 261)

Building exposures	Number	Mean	Percentage (%)	SD	Missing
Presence of pests
Cockroaches					–
No	67		25.67
Yes	194		74.33
Rodents					–
No	149		57.09
Yes	112		42.91
Building type
Public housing					–
No	221		84.67
Yes	40		15.33
Commercial/Residential housing					–
No (residential housing only)	217		83.14
Yes	44		16.86
Building size					47
House/Duplex	50		23.36
Low-rise (<8 floors)	126		58.88
High-rise (8+ floors)	38		17.76
Building condition
Building age		68.86		21.97	1
Environmental control board violations		0.19		0.95	1
Mother’s demographic characteristics
Mother has health insurance	250		95.79		–
Mother ever had asthma	168		64.37		–
Mother ever had hay fever	91		34.87		–
Mother ever had other allergies	202		77.39		–
Marital status					–
Married	75		28.74
Divorced	7		2.68
Separated	9		3.45
Widowed	1		0.38
Never been married	169		64.75
Mother’s birth place					–
Mainland USA	192		73.56
Puerto Rico	54		20.69
Dominican Republic	10		3.83
Mexico	2		0.77
Other	3		1.15
Education					–
High school grad or equivalent, or less	147		56.32
Some college or more	114		43.68
Income					–
≤$39,999	211		80.84
$40,000+	50		19.16
Mother years in the USA		23.44		7.12	–

Table 2.

Indoor allergens at baseline

	Number	Median	Missing	Geometric mean	Geometric SD
Der f 1 mg/g (dust mites)	245	0.13	16	0.20	2.98
Fel d 1 mg/g(cat)	253	0.48	8	0.64	7.66
Bla g 2 U/g (40 ng/g) (cockroach)	221	0.50	40	1.46	4.10
MUP mg/g (mouse)	241	0.38	20	0.63	2.81

Bivariate and Multivariable Analysis

We examined the association of household indoor allergens and building-level characteristics in a cohort of Puerto Ricans in the Bronx.

Dust Mite Allergen Table 3 shows a bivariate, statistically significant association between the household-reported presence of rodents and the presence of dust allergen (1.34; 95% CI, 1.02, 1.77). In fully adjusted linear models, this relationship became borderline statistically significant (1.37; 95% CI, 0.99, 1.90). In fully adjusted logistic models, there was a (borderline) statistically significant association between the household-reported presence of rodents and the existence of dust allergen (>1.6 μg/g) (OR, 2.18; 95% CI, 1.01, 4.68).

Table 3.

Bivariate and multivariable associations of building characteristics and indoor allergens: Puerto Rican Asthma Project (n = 261)

	Dust mite allergen (Der f 1)			Cat allergen (Fel d 1)			Cockroach allergen (Bla g 2)			Mouse allergen (MUP)
	Bivariatea	Multivariableab	Logisticb	Bivariatea	Multivariableab	Logisticb	Bivariatea	Multivariableab	Logisticb	Bivariatea	Multivariableab	Logisticb
Presence of pests
No cockroaches (reference)
Cockroaches	1.08 (0.79, 1.49)	1.02 (0.67, 1.56)	1.05 (0.39, 2.80)	0.99 (0.55, 1.78)	0.52 (0.25, 1.10)	0.44 (0.19, 1.02)	2.72 (1.80, 4.12)	2.07 (1.23, 3.49)	2.82 (1.10, 7.19)	1.24 (0.92, 1.67)	1.33 (0.94, 1.89)	2.64 (0.68, 10.27)
No rodents (reference)
Rodents	1.34 (1.02, 1.77)	1.37 (0.99, 1.90)	2.18 (1.01, 4.68)	0.68 (0.41, 1.12)	0.62 (0.35, 1.09)	0.82 (0.43, 1.55)	1.11 (0.77, 1.62)	0.88 (0.59, 1.31)	1.01 (0.51, 1.97)	1.72 (1.33, 2.22)	1.70 (1.29, 2.23)	4.79 (1.69, 13.61)
Building type
Not public housing (reference)
Public housing	0.91 (0.63,1.32)	1.00 (0.57, 1.76)	0.86 (0.21, 3.53)	1.00 (0.50, 1.99)	0.69 (0.25, 1.91)	0.38 (0.10, 1.38)	3.28 (2.02, 5.32)	2.14 (1.07, 4.31)	2.78 (0.83, 9.30)	0.83 (0.58, 1.19)	1.31 (0.79, 2.15)	6.20 (1.01, 37.95)
Residential housing (reference)
Commercial/Residential housing	0.82 (0.57, 1.19)	0.79 (0.52, 1.20)	0.65 (0.23, 1.87)	1.20 (0.62, 2.35)	1.28 (0.61, 2.69)	1.82 (0.82, 4.03)	0.81 (0.50, 1.31)	0.67 (0.41, 1.10)	0.74 (0.33, 1.70)	1.32 (0.94, 1.86)	1.01 (0.71, 1.44)	1.42 (0.47, 4.29)
Building size
House/Duplex (reference)
Low-rise	0.91 (0.62, 1.34)	0.81 (0.52, 1.25)	0.51 (0.19, 1.34)	1.17 (0.59, 2.30)	1.40 (0.65, 3.03)	1.29 (0.54, 3.08)	1.44 (0.88, 2.36)	0.92 (0.55, 1.56)	1.04 (0.42, 2.56)	0.86 (0.61, 1.22)	0.60 (0.42, 0.87)	0.16 (0.05, 0.52)
High-rise	0.75 (0.46, 1.22)	0.76 (0.40, 1.44)	0.44 (0.09, 2.13)	1.13 (0.48, 2.70)	2.34 (0.73, 7.54)	6.29 (1.51, 26.21)	3.42 (1.82, 6.44)	1.48 (0.67, 3.27)	2.36 (0.59, 9.39)	0.82 (0.52, 1.29)	0.50 (0.29, 0.88)	0.06 (0.01, 0.50)
Building condition
Age of building	1.00 (1.00, 1.01)	1.00 (1.00, 1.01)	1.00 (0.98, 1.02)	1.00 (1.00, 1.01)	1.01 (1.00, 1.03)	1.03 (1.01, 1.05)	1.00 (0.99, 1.01)	1.01 (1.00, 1.02)	1.02 (1.00, 1.04)	1.01 (1.00, 1.01)	1.00 (1.00, 1.01)	1.02 (1.00, 1.05)
Environmental control board violations	1.01 (0.87, 1.16)	1.02 (0.88, 1.19)	1.00 (0.67, 1.48)	0.91 (0.70, 1.19)	0.96 (0.73, 1.26)	0.56 (0.21, 1.50)	0.91 (0.75, 1.09)	1.02 (0.86, 1.21)	1.00 (0.55, 1.82)	0.96 (0.84, 1.09)	0.99 (0.87, 1.12)	0.63 (0.14, 2.81)

Mean roadway length: (1) 396.4, (2) 556.2, and (3) 713.3. Housing code violations/1,000 rental units: (a) 39.0 (n = 70), (b) 78.8 (n = 91), and (c) 179.3 (n = 99)

^aRatios and the 95% confidence intervals were back-transformed to original scale instead of log scale

^bMultivariable and logistic results: each parameter estimate is adjusted for all other variables in the model, including income and education

Cat Allergen Table 3 displays there were no statistically significant associations in any bivariate or multivariable linear models between building-level characteristics and cat allergen. In fully adjusted logistic models, there was a statistically significant relationship between living in a high-rise apartment vs. a house/duplex and the existence of cat allergen (>1 μg/g; OR, 6.29; 95% CI, 1.51, 26.21). There was also a borderline statistically significant relationship between building age and the existence of cat allergen (>1 μg/g; OR, 1.03; 95% CI, 1.01, 1.05). This relationship remained borderline statistically significant when we stratified for owning a cat (OR, 1.04; 95% CI, 1.01, 1.06).

Cockroach Allergen Table 3 displays the household-reported presence of cockroaches (2.72; 95% CI, 1.80, 4.12), living in public housing (3.28; 95% CI, 2.02, 5.32), and living in a high-rise apartment building (3.42; 95% CI, 1.82, 6.44) were statistically significantly associated with the existence of cockroach allergen in bivariate linear models. In fully adjusted linear models, the household-reported presence of cockroaches (2.07; 95% CI, 1.23, 3.49) and living in public housing (2.14; 95% CI, 1.07, 4.31) remained statistically significantly associated with the existence of cockroach allergen. In fully adjusted logistic models, there was a statistically significant relationship between the household-reported presence of cockroaches and the existence of cockroach allergen (>1 U/g; OR, 2.82; 95% CI, 1.10, 7.19).

Mouse Allergen Table 3 shows the household-reported presence of rodents (1.72; 95% CI, 1.33, 2.22) was statistically significantly associated with the existence of mouse allergen in bivariate linear models. In fully adjusted linear models, the household-reported presence of rodents was positively statistically significantly associated with the existence of mouse allergen (1.70; 95% CI, 1.29, 2.23); however, living in a low-rise apartment building (0.60; 95% CI, 0.42, 0.87) and living in a high-rise apartment building (0.50; 95% CI, 0.29, 0.88), compared with the referent group (duplex/house), was negatively associated with the existence of mouse allergen. In fully adjusted logistic models, there was also a statistically significant relationship between the household-reported presence of rodents and the existence of mouse allergen (>1.6 μg/g). (OR, 4.79; 95% CI, 1.69,13.61). Likewise, there was a statistically significant association between the existence of mouse allergen (>1.6 μg/g) and living in public housing (6.20; 95% CI, 1.01, 37.95), and between the existence of mouse allergen (>1.6 μg/g) and building size: living in a low-rise apartment (0.16; 95% CI, 0.05, 0.52) or high-rise apartment (0.06; 95% CI, 0.01, 0.50) vs. a duplex/house.

Discussion

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 respectively.

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

Limitations

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).

Implications

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 Research

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.