Time trends. A study conducted in two provinces in the West found that pneumonia incidence in children ,5 years of age decreased from 1997 to 2000 by 64% in Yunnan province (0.083 in 1997 versus 0.030 episodes per person-year in 2000) and by 47% in Qinghai province (0.017 in 1997 versus 0.009 in 2000) [21] .