Comprehensive avoidance of dust mite allergens Multifaceted primary prevention studies

Public Health Significance of Urban Pests 31 loping asthma at age 2 years than did controls called the placebo group, but no diffe- rences in sensitization or other symptoms at ages 2 or 4 years Koopman et al., 2002; Corver et al., 2006. One complication reported by the authors of this study was an unex- plained lower dust mite allergen level 2- to 10-fold in the cohort active and placebo than reported previously in the Netherlands Brunekreef et al., 2005. A multinational European study that used mattress covers and education on mite allergen reduction also found no difference in sensitization or symptoms indicative of developing asthma at age 2 years Horak et al., 2004. It is important to note that many of the homes still contai- ned carpets a reservoir for dust mites at the follow-up assessment. Also, mite allergen levels were not measured, so the effect of avoiding exposure to allergens could not be eva- luated. Two other European studies, using mattress encasement and education, have attempted primary prevention of sensitization in older, high-risk children. Children in the active group of both a cohort of toddlers and preschool children mean age: 3 years and a cohort of 5–7-year olds who were at risk of developing sensitization atopic parent or sensitized to other aeroallergens were less likely than controls to develop sensitiza- tion to dust mite allergens Arshad et al., 2002; Tsitoura et al., 2002. Both of these stu- dies demonstrated effective primary prevention of sensitization, but only over a short period of time. Further follow-up at later ages is required to determine the long-term efficacy.

1.7.2.2. Comprehensive avoidance of dust mite allergens

Dust mite allergen levels were lowered for the active group in more stringent environ- mental interventions. In a Manchester, England, intervention study, homes received aller- gen impermeable covers for both the mother’s bed and the child’s bed, a high filtration vacuum cleaner, vinyl flooring in the child’s bedroom after removing carpets, bedding that was washed weekly in hot water and washable toys. At age 3 years, there was no significant difference in the symptoms reported, but airway resistance was significantly better in the active group. Unexpectedly, the children in the active group were signifi- cantly more likely than the children in the control group to be sensitized to dust mite allergens at age 3 years Woodcock et al., 2004. A less stringent intervention study in Australia also reduced allergen levels significantly Marks et al., 2006. Dust mite avoidance measures in the active group included allergen impermeable covers, weekly washing of bedding in hot water and education about dust mite avoidance. At age 5 years, there was no difference in the prevalence of asthma, eczema or atopy between the active and placebo groups. The authors cited several rea- sons for the failure of the intervention, including that while allergen levels were signifi- cantly reduced in the active group, they may not have been low enough to be clinically relevant. They also discussed the possible need for a multifaceted intervention, as was discussed in the previous section on tertiary prevention.

1.7.2.3. Multifaceted primary prevention studies

From the studies discussed in the previous two sections, it appears that reducing exposure to allergens alone may not be a sufficient avoidance measure for primary prevention – at least for outcomes in the early years of life. A large multifaceted trial in Canada inclu- ded control of house dust mites in multiple locations in the home, a reduction in expo- Allergic asthma 30 decrease with a substantial reduction orders of magnitude in the pollen allergen, domes- tic allergen reduction for the tertiary prevention of asthma is compelling. However, the efficacy of methods currently used for allergen reduction and whether they should be recommended for asthmatic individuals are controversial O’Connor, 2005. While sin- gle-allergen, single-site allergen-avoidance strategies such as the use of allergen imper- meable mattress covers do not seem effective on their own, recent evidence has shown that multifaceted domestic avoidance measures, which include targeting multiple aller- gens and multiple sites, have some benefit among children who live in urban environ- ments.

1.7.2. Primary and secondary prevention