Effect of desert dust exposure on allergic symptoms: A natural experiment in Japan

Abstract Background Desert dust originating from arid and semiarid areas is transported to widespread regions, including Japan. Desert dust particles exert adjuvant effects in animals. Objective To examine whether desert dust enhances allergic symptoms in real-life settings and to explore its effect modifiers. Methods We conducted an observational study of 3,327 pregnant women during spring and fall in October 2011 to May 2013 in 3 regions in Japan as an adjunct study of the Japan Environment & Children's Study. We acquired participants' daily symptom scores by sending a questionnaire to their mobile phones on high desert-dust days (>0.07/km) and on some randomly selected other days (control days) for each participant. Results Pregnant women had an increased risk of allergic symptoms on high desert-dust days (adjusted odds ratio [OR], 1.10; 95% CI, 1.04–1.18). The increased OR was mostly driven by those who showed positive IgE to Japanese cedar pollen when pollen simultaneously dispersed (adjusted OR, 1.25; 95% CI, 1.13–1.38), whereas no clear risk increase was observed in the absence of pollen or for participants with negative IgE to Japanese cedar pollen. The risk elevation was observed from low levels of desert dust in a dose-dependent manner even on control days. Conclusion Ambient desert dust level was associated with an increased risk of allergic symptoms in pollen-sensitized pregnant women when pollen was present in the air. The risk increase was dose dependent and was observed from low levels of desert dust. These results support a hypothesis that ambient desert dust particles exert adjuvant effects in human in real-life settings. Trial Registration clinicaltrials.gov Identifier: UMIN000010826.