tokens: The authors investigate in a group of 211 children aged 2 - 6 years , incl . in particular a group of 33 2 - year - old ones , in 1990 and checked in 1991 at two sites in Bratislava - - a town with a varying concentration of NOX , SO2 , dustiness and dust fallout - - their influence on the incidence , type and course of relapsing respiratory disease .