Wang Muramic acid, a constituent of peptidoglycant in gram- negative and gram-positive bacteria in the environment, was suggested to be an additional marker of microbial exposure (van Strien et al 2004). A recent study was conducted on 553 farm and non-farm school children from Austria, Switzerland, and Germany. Their mattress dust muramic acid concentrations were determined and their health condition was assessed by using IgE measurements and questionnaire information. The muramic acid concentration was found to be significantly higher in dust from farm children’s mattresses than in dust from non-farm children’s mattresses (157 ng/mg vs 131 ng/mg). Interestingly, children with higher mattress dust muramic acid concentrations had a significantly lower prevalence of wheezing regardless of farming status and endotoxin exposure (van Strien et al 2004). House dust mites House-dust mites (HDM) are the most common indoor allergens for allergic diseases such as allergic rhinitis and asthma. International studies have demonstrated that Dermatophagoides pteronyssinus (Der p), Dermatophagoides farinae (Der f) are the most common mite species worldwide (Bousquet et al 2001). In the tropics, Blomia tropicalis (B. tropicalis), another dust mite species, was found to be the most prevalent domestic mite (Zhang et al 1997; Wang et al 2003; Fernandez-Caldas and Lockey 2004). HDM are commonly found in association with bedding products, carpets, curtains, and fabric products. HDM hypersensitivity is strongly associated with persistent allergic rhinitis (PAR). Allergen avoidance, including house dust mites, is recommended to be an integral part of a management strategy for allergic rhinitis and asthma (Bousquet et al 2001). The real challenge is to create a low allergen environment in patients’ homes, and unfortunately, the majority of single interventions have failed to achieve a sufficient reduction in allergen load leading to a clinical improvement (Bousquet et al 2001). It is possible to reduce the concentration of house dust mites either by chemicals (tannic acid or solidified benzyl benzoate) or bedding encasings. House dust mite encasement products such as pillow and mattress covers are widely available for sale. Reimbursement from insurance companies for the purchase of such products in the United States is estimated at $42 million in 2001 (Terrehorst et al 2003). Although laboratory studies have demonstrated the high filtering capabilities of these barrier products, surprisingly, few clinical trials studies have been done to 120 date reporting the clinical efficacy of such prevention methods (Sheikh and Huwitz 2001). A multicentered, randomized, placebo-controlled study has been done so far to evaluate the efficacy of HDM impermeable bedding covers in the bedrooms of patients with allergic rhinitis, showing no significant improvement on clinical symptoms between treatment and control groups (Terrehorst et al 2003). This may be due to the high HDM load from other non-bedding products common in the home environment that may confound the results of the study. It is commonly understood that exposure to HDM allergen in infancy increases the risk of developing asthma. However, a recent study was unable to find any relationship between the level of HDM allergen exposure in children’s bedrooms in early childhood and development of bronchial hyperresponsiveness or physician-diagnosed asthma by age 6–7 years (Carter et al 2003). Another study was performed to compare the association between dust mite allergen level and asthma symptom prevalence across multiple countries in the Asia-Pacific region. Among children aged 6–7 years, neither allergen (Der p 1 and Der f 1) was related to asthmatic symptoms or severity prevalence (Wickens et al 2004). To address this conflicting issue, one needs sensitive measures to assess quantitatively and qualitatively the HDM exposure, as well as the exposure to other adjuvant factors in the home. The relationships between house and household characteristics and allergen concentrations in both air and dust were complex (Peterson et al 2003). The concentrations of Der f 1 in dust increased with increasing number of residents and relative humidity and declined when forced air heating was used. Dust concentrations of Der p 1 were lower in new homes and during forced air heating use but higher with higher relative humidity and in the presence of dogs. A study was performed to compare indoor allergens (Der p 1 and Der f 1) and endotoxin levels between urban and rural settings as important determinants for asthma and atopy in children. The results showed that indoor environmental factors such as dampness seemed to be important determinants for allergen and endotoxin, but living habits such as lack of mattress cover appeared unimportant (Wickens et al 2004). In the tropics, the majority of allergic rhinitis is persistent in nature (Wang et al 2002). The year-round warm and humid climate is conducive to the proliferation of dust mites and molds, two of the most common aeroallergens implicated in persistent allergic rhinitis (Wang et al 2003). As patients with persistent allergic rhinitis are often symptomatic throughout the year and need long-term control of HDM Therapeutics and Clinical Risk Management 2005:1(2)