Study On The Trends In Exposure To Secondhand Smoke Among Chinese Mainland Adults

Background:The prevalence of exposure to secondhand smoke (SHS) has been very high in China so as to cause great harm to people’s health. From1984to2010, four nationwide tobacco epidemiological questionnaire-based surveys were conducted, the results of which showed an upward trend in exposure levels to SHS among Chinese mainland adults. However, as the definitions of exposure to SHS were different among those surveys, it is still in doubt whether or not the exposure levels to SHS increased. Thus, it is necessary to describe the trend of SHS exposure in China on the basis of the unified exposure definition.Objective:This study aimed to find the relationship of prevalence of SHS measured by different exposure definitions, and to describe the trend of the exposure levels to SHS in Chinese mainland population over a period of15years from1996to2010with the unified definition.Methods:1. Definitions of exposure to SHS in questionnaire-based surveys were reviewed and classified into3types consisting of light, medium and heavy exposure to SHS. Total exposure included all3types of exposure.2. The program-"Building epidemiology, surveillance and intervention capacity of tobacco control in China" supported by NIH Fogarty International Center has completed survey with various questions to measure the SHS exposure. My study used the original data from the above program to analyze the relationship of different definitions of SHS exposure, in other words, the relationship of prevalence of medium-heavy exposure and total exposure. Methods included imputation of missing data, comparison of the two type of exposure with different questionnaires, and establishment of regression models of prevalence measured by the two exposure definitions. Qualitative study was further conducted to find reasons on people’s responses towards different exposure definitions with various questionnaires.3. With standard screening and inclusion criteria, a systematic review and Meta-analysis were undertaken to synthesis evidence of the prevalence of exposure to SHS in mainland China reported by both national and local surveys. Data from all surveys satisfying the inclusion criteria were adjusted to the unified definition with the regression models, and then the adjusted data were pooled to Meta-analysis.4. The prevalence trend of SHS exposure was described by regression model with adjusted results.Results:1. There were significant disparity of SHS exposure measured by medium-heavy exposure definition and total exposure definition. The prevalence of SHS exposure mesured by total exposure definition was23.23%higher than that measured by medium-heavy exposure definition. With "15minutes" in the questionnaire and "less than a day in a typical week" in the multiple-choice options, the measurement of medium-heavy exposure definition categorized a certain amount of people with light exposure into those without exposure. The concept of "SHS" and "exposure" presented in the questionnaire also influenced respondents’ choices on SHS exposure. Medium-heavy exposure measured by fill-in-the-blank question was10%lower than that measured by multiple-choice question in the questionnaire.2. During1996-2005, the prevalence of medium-heavy exposure to SHS declined notably from53.48%to32.51%. Similarly, among urban, rural areas and different age-groups, the prevalence decreased by about19percent point. The proportion of medium-heavy exposure to SHS among male and female dropped by14.76and23.29percent, respectively. However, from2005to2010, medium-heavy exposure to SHS didn’t change much, and experienced a fluctuation between30%和and40%.3. The prevalence of total exposure to SHS declined by13.06percent, from65.52%in1996to52.76%in2005. The declining proportion were13.14%and11.95%in urban and rural areas,8.5%in male,15.25%in female, and approximately11%in both15-44and above45age-groups. After the year2005, an increasing trend was observed in the total exposure, with the prevalence52.46%in2005and63.81%in2010. The proportion of people exposed to SHS through2005to2010raised by6.1percent in urban areas,7.22percent in rural areas,11.34percent among male and9.24percent among female. And total exposure increased by about16percent among people both under and above45.Conclusions:1. Along with further understanding of the health risks caused by exposure to SHS, the definition of SHS exposure has gradually evolved. Therefore, the real trend in exposure to SHS can be described only if the definitions are unified.2. After unifying definitions, we find that medium-heavy exposure to SHS took a substantial decline during the period of1996-2010, especially before the year2005, but it hardly decreased between2005and2010. By contrast, total exposure didn’t show significant change, with a decrease from1996to2005and a rise from2005to2010.3. This trend patterns were also observed across all population subgroups (gender, area and age-group). The prevalence of SHS exposure decreased more notably in female than in male, and more in urban areas than in rural areas.