Pest counts Allergen assays

Public Health Significance of Urban Pests Allergic asthma 17 16 Rauh et al., 2002; Stelmach et al., 2002a, 2002b; Chew et al., 2003; Cohn et al., 2004; Matsui et al., 2005. For example, the United States National Survey of Lead and Allergens in Housing, which included information from buildings in 75 locations, found that the level of mouse allergens was higher in high-rise buildings five storeys or more than in low- rise apartments one to four storeys Cohn et al., 2004. This finding is not directly appli- cable to some cities, such as New York City, where the majority of the housing in low- income neighbourhoods is greater than five storeys. In fact, shorter apartment buildings fewer than eight storeys in New York City were more likely to have high levels of mouse allergen in the kitchen and bed dust than taller high-rise buildings OR = 10 and 6.25, for kitchen and bed dust, respectively Chew et al., 2003. This highlights the impor- tance of considering the geographic factors that influence allergen levels within the home. However, some predictors, such as resident reports of mice or cockroaches, are consis- tently associated with high levels of their respective allergens Chew et al., 1998; Phipatanakul et al., 2000a; Rauh et al., 2002; Cohn et al., 2004; Matsui et al., 2004a. The use of a standardized questionnaire, such as that employed by the large analysis and review of European housing and health status LARES project, can enable the survey of larger populations and comparisons across study sites when allergen measurements are not feasible, but care must be taken in the interpretation, for the reasons noted in this sec- tion WHO Regional Office for Europe, 2006.

1.2.2. Pest counts

Before immunoassays were developed, exposure to dust mites was assessed by trained acarologists who identified and counted dust mites in house dust. Subsequently, mite counts were shown to correlate with allergen concentrations in the dust Platts-Mills et al., 1992. Other investigators have made measurements of faecal pellets which contain guanine and found significant associations with dust mite allergens Tovey et al., 1981; van Bronswijk et al., 1989, but the development of allergen assays has enabled cost- and time-effective assessments of exposure that do not depend on the expertise of acarolo- gists. The main problem with bypassing the identification step is that many environments have more than one type of dust mite Arlian et al., 1992; Montealegre et al., 1997; Warner et al., 1998, and the use of a single dust mite allergen immunoassay see section 1.2.3 could preclude finding meaningful etiological agents of allergic disease. Correlations between cockroaches and cockroach-allergen levels in urban homes have been observed; a major cockroach allergen, Bla g 2 from the German cockroach, Blatella germanica , was positively correlated with cockroaches collected on sticky traps in bedrooms r = 0.63, P 0.001 and in kitchens r = 0.53, P 0.001 McConnell et al., 2003. A study of low-income suburban homes found that the number of cockroaches collected on sticky traps correlated best with the allergens in dust sampled two months after trap collection Mollet et al., 1997. Of note is that cockroach allergen was still detectable in kit- chen and bed dust samples, even when no cockroaches were detected.

1.2.3. Allergen assays

Serum IgE antibodies from allergic individuals have been used to identify the relevant allergenic proteins from allergen sources. Enzyme-linked immunosorbent assays ELISAs were subsequently developed to measure these relevant proteins from cockroa- ches, mice, rats and dust mites in dust and air samples Chapman et al., 1987; Pollart et al., 1991a; Renstrom et al., 1997; Ferrari et al., 2004. The ELISAs differ somewhat depending on which allergen is being measured, but most use a sandwich method with primary mono- clonal capture antibodies bound to a plastic surface. The quantity of an allergen-specific secondary antibody is detected by a colorimetric enzymatic reaction. These immunoassays demonstrate a high degree of sensitivity and specificity, with nanogram quantities of pro- tein detectable with little cross-reactivity between allergens. Since ELISAs involve an anti- body or antigen interaction, they are susceptible to interference from contaminants in the dust samples Woodfolk et al., 1994; Chew et al., 1999b. With the antibodies used in the ELISA, rapid screens have been developed and enable a quick assessment of allergen levels in the home or workplace without the use of major laboratory facilities. The results from the rapid test are not as quantitative as those obtained by ELISA, but they do correlate well with those obtained by ELISA Chapman, Tsay Vailes, 2001; Lau et al., 2001.

1.2.4. Dust sampling