National Survey of Lead and Allergens in Housing (NSLAH)
Environmental Cardiopulmonary Disease Group
The National Survey of Lead and Allergens in Housing (NSLAH) was the first population-based study to provide information about how levels of indoor allergens and endotoxin vary in U.S. homes. The NSLAH surveyed a nationally representative sample of 831 housing units, inhabited by 2,456 individuals, in 75 different locations throughout the U.S. ( Vojta et al., Env. Health Perspect., 2002; Jacobs et al., Env. Health Perspect., 2002). Information on demographics, household characteristics, and occupant health status was collected by a questionnaire. Environmental data were acquired by sample collection and inspection of the housing units.
Characteristics of indoor allergen and endotoxin exposures in U.S. homes
Allergen measurements were available from at least one room for 99 percent of the homes. For endotoxin, the corresponding percentage was 95 percent (Salo et al. J Allergy Clin Immunol., 2008). Alternaria, cat (Fel d 1) and dog (Can f 1) allergens were the most commonly detected allergens; virtually all homes (>99 percent) had detectable levels in at least 1 sampling location. Detectable levels of dust mite allergens (Der f 1 and Der p 1) were found in at least 85 percent of the surveyed homes, and mouse (MUP) and cockroach (Bla g 1) allergens were detected in 82 percent and 63 percent of the households, respectively. Of the dust mite allergens, Der f 1 had highest levels in bedrooms; Alternaria, cat, and dog allergens were found to be highest in living rooms; and mouse and cockroach allergen levels tended to be highest in kitchens. The NSLAH data have demonstrated that individual allergen levels are strongly associated with regional, racial/ethnic, and socioeconomic factors, although each allergen appears to have a distinct set of predictors (Arbes et al., J. Allergy Clin. Immunol., 2003), (Arbes et al., J. Allergy Clin. Immunol., 2004), (Cohn et al., J. Allergy Clin. Immunol., 2004), (Salo et al., J. Allergy Clinical Immunol., 2005), (Cohn et al., Env. Health Perspect., 2006).
Exposure to multiple allergens was common in U.S. homes. Of the surveyed homes, 52 percent had at least 6 detectable 5 allergens and 46 percent had at least 3 allergens exceeding elevated levels. The following cut points were used to define elevated allergen levels: 10 μg/g for Der p 1, Der f 1 and Can f 1; 8 μg/g for Fel d 1; 8 U/g Bla g 1; 1.6 μg/g for mouse urinary protein; and 7 μg/g for Alternaria. Several factors contributed to increased concentrations of allergens. Types and levels of allergens were influenced by sociodemographic factors, including race/ethnicity, income, and type of home, and sources of allergens, such as presence of pets and pests. Allergen burden was also strongly associated with endotoxin levels in the home. The levels of endotoxin depended on location sampled within the home and region of the country (Thorne et al., Environ Health Perspect, 2009). Endotoxin concentrations increased with the number of occupants, particularly children, presence of dogs, lower educational level, living in poverty, observed food debris, and evidence of cockroach infestation and smoking.
Indoor allergen and endotoxin exposures in relation to asthma
In the NSLAH, lifetime prevalence of doctor-diagnosed asthma was 11.2 percent, and 6.9 percent of the study subjects reported asthma symptoms in the past 12 months. The majority of the current asthmatics reported doctor-diagnosed allergies (77 percent) and used asthma medication (71 percent). The NSLAH data showed that homes of asthmatic subjects were more likely to have a greater number of allergens exceeding increased levels than homes in which no asthmatics resided (Salo et al. J Allergy Clin Immunol., 2008). The results highlighted the important role of indoor allergen exposures in asthma exacerbations. Among allergic individuals, high burden of allergens in the home significantly increased the likelihood of having asthma symptoms. However, the relationship between allergen exposure and asthma is complex and varies by allergen type. For example, exposure to elevated mouse allergen levels significantly increased the likelihood of asthma symptoms only in allergic individuals (Salo et al., Environ Health Perspect., 2009), whereas elevated Alternaria levels in the home increased the likelihood of having asthma symptoms irrespective of subject's allergic status (Salo et al., J Allergy Clin Immunol., 2006). The NSLAH results also suggested that asthma-related symptoms are influenced by endotoxin levels and total dust exposure in the home ( Thorne et al., Am. J. Resp. Crit. Care Med., 2005; Elliott et al., Environ Health Perspect., 2007).
This nationally representative survey has:
- Provided estimates of indoor allergen and endotoxin exposure in the U.S. population
- Provided a baseline that can be used as a reference point for future allergen surveys
- Facilitated evaluation of regional, ethnic, socioeconomic, and housing characteristic differences in the allergen burden
- Demonstrated that exposure to allergens and endotoxin in the home environment is important in asthma pathogenesis