Exposure to Japanese cedar pollen in early life and subsequent sensitization to Japanese cedar pollen.

The effect of exposure to Japanese cedar pollen (JCP) in early life on subsequent sensitization to it was evaluated. Specific IgE antibody to JCP was examined in 440-504 school children in a rural town each year during 1995-98. The amount of dispersed pollen measured by a Durham sampler widely ranged from 165 to 5941 grains/cm2/year during this period. The amount had been measured during the period of 1982-91 in which these children were born, and it also widely ranged from 148 to 8566 grains/cm2/year. Children born during November to January, who were exposed to JCP within 6 months of age, increased at the risk of sensitization to JCP, especially severe sensitization, relative to those born in the other months. Age-adjusted prevalence rate ratio (RR) of having a JCP-IgE > or = 15 U/ml (control; < 0.35 U/ml) for children born in December to February relative to children born in the other months was 1.74 (95% confidence interval; 1.06-2.87, examined in 1998), and for those born in November to January was 1.57 (95% CI; 1.00-2.46, examined in 1997). The risk of sensitization to JCP was low for those born in May to July (RR = 0.42, 95% CI; 0.19-0.93, examined in 1998). There was also a strong correlation between the amount of the dispersed pollen during the period of 2-6 months after birth and the prevalence of sensitization to JCP.