dust mite occur than in comparison populations at lower altitudes (Martigues for children and Marseilles for adults) (D. Charpin et al., 1988a, 1991; Vervloet et al., 1979). Analyses of house dust from Briançon found lower levels of house dust mite compared with the levels in dust from low-altitude homes (see Table 2-3). In addition, Sporik and colleagues (1990) demonstrated a trend toward an increasing degree of sensitization among children at age 11 with greater dust mite exposure at age 1. Chapter 6 analyzes these and other studies and suggests that there may be an exposure-response relationship between dust mite exposure and the prevalence of skin test reactivity (sensitization).
Exposure to environmental tobacco smoke is another example of an environmental risk factor in that it appears to be associated with increased skin test reactivity in children (Burrows and Martinez, 1989) and a twofold increase in serum IgE in infants (Zeiger, 1988). Zeiger also discussed the possible effects of exposure to ingestants and microbial agents on the risk