Fig. 2. Effect of combined exposure to both PM2.5 and ETS according to exposure time on susceptibility to (A) lower and (B) upper respiratory tract infections in infancy. The groups were stratified by exposure time: (a) prenatal PM2.5/prenatal ETS; (b) prenatal PM2.5/postnatal ETS; (c) postnatal PM2.5/prenatal ETS; and (d) postnatal PM2.5/postnatal ETS. Prenatal high indoor PM2.5 and ETS exposure acted additively to increase the risk of lower respiratory tract infections. *Adjustments for maternal age at delivery, maternal body mass index, maternal educational degree, gestational age, delivery mode, infant sex, and family history of allergy. ETS, environmental tobacco smoke; PM2.5, fine particulate matter.
