Childhood asthma in Beijing, China: a population-based case-control study.

China is the most populous country in the world. Few studies, however, have been conducted there to investigate the risk factors for childhood asthma. A population-based case-control study was conducted in Shunyi County, People's Republic of China, in January 1999 and March 2001 to investigate the issue. An increased risk of childhood asthma was associated with smoking by relatives in front of the mother while she was pregnant with the child (odds ratio (OR) = 1.3, 95% confidence interval (CI): 1.0, 1.6) and with smoking by relatives in front of the child (OR = 1.4, 95% CI: 1.1, 1.9). The risk increased with the increasing number of smokers and the total minutes of smoking by relatives in front of both the child and the mother while she was pregnant with the child. An increased risk was observed for use of coal for heating (OR = 1.5, 95% CI: 1.1, 1.9). Those who reported using coal for cooking without ventilation also had an increased risk (OR = 2.3, 95% CI: 1.5, 3.5). An increased risk was observed for those who reported having molds or fungi on the ceilings of their houses (OR = 1.8, 95% CI: 1.1, 2.9) or inside the child's room (OR = 1.8, 95% CI: 1.0, 3.2). An increased risk was also found for those having both a dog and a cat as pets (OR = 1.5, 95% CI: 1.0, 2.3) or for finding both cockroaches and rats inside their houses (OR = 1.8, 95% CI: 1.2, 2.8).