highly significantP < .001
The prevalence in different age groups showed a downward gradient, which was highly significant for rhinitis ( P < .001), conjunctivitis ( P < .001) and for asthma ( P < .01) ( S5 Fig ).
The prevalence in different age groups showed a downward gradient, which was highly significant for rhinitis ( P < .001), conjunctivitis ( P < .001) and for asthma ( P < .01) ( S5 Fig ).