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RESEARCH ARTICLE Open Access

Patterns and socioeconomic influences of tobacco exposure in tobacco cultivating rural areas of Yunnan Province, China Le Cai1*, Xinan Wu1, Abhinav Goyal2, Yuntao Han1, Wenlong Cui1, Xia Xiao1, Jianhui He1, Keying Zhao1, Ying Song1 and Feng Jiao1

Abstract

Background: This study describes the patterns and socioeconomic influences of tobacco use among adults in tobacco-cultivating regions of rural southwest China.

Methods: A cross-sectional survey was conducted in 8681 adults aged ≥18 years in rural areas of Yunnan Province, China from 2010 to 2011. A standardized questionnaire was administered to obtain data about participants’ demographic characteristics, individual socioeconomic status, ethnicity, self-reported smoking habits, and exposure to secondhand smoke (SHS). The socioeconomic predictors of current smoking, nicotine addiction, and SHS exposure were analyzed using multivariate logistic regression.

Results: The prevalence rates of tobacco use were much higher in men compared with women (current smoking 68.5% vs. 1.3%; and nicotine dependence 85.2% vs. 72.7%). However, the rate of SHS exposure was higher in women compared with men (76.6% vs. 70.5%). Tobacco farmers had higher prevalence rates of current smoking, nicotine dependence, and SHS exposure compared with participants not engaged in tobacco farming (P<0.01). Most tobacco users (84.5%) reported initiating smoking during adolescence. A total of 81.1% of smokers smoked in public places, and 77.6% smoked in workplaces. Individuals belonging to an ethnic minority had a lower probability of SHS exposure and nicotine dependence. Individual educational level was found to be inversely associated with the prevalence of current smoking, exposure to SHS, and nicotine dependence. Higher annual household income was associated with a greater risk of nicotine dependence.

Conclusions: This study suggests that tobacco control efforts in rural southwest China must be tailored to address tobacco-cultivating status and socioeconomic factors.

Keywords: Smoking, Exposure to secondhand smoke, Socioeconomic status, China

Background The health effects of smoking and exposure to second- hand smoke (SHS) are major global public health issues. The World Health Organization reported that tobacco use in the 20th century resulted in 100 million deaths worldwide [1], and this number is projected to increase to 1 billion deaths in the 21st century. China is the most important battleground in the struggle against tobacco use globally, and it is both the world’s largest producer

and consumer of tobacco products. China is home to an estimated 301 million current smokers in 2010, and the rising trends in tobacco consumption are alarming [2]. The 2002 national survey reported that 51.9% of non- smokers in China were regularly exposed to SHS [3]. Correspondingly, China also experiences a high inci- dence of tobacco-related diseases [4]. A previous Chin- ese study indicates that a total of 673,000 deaths in Chinese adults were attributable to smoking in 2005 [5], with cancer, cardiovascular disease, and respiratory dis- ease accounting for most of these deaths. Smoking is highly prevalent, and its impact on premature death has become a major concern in China.

* Correspondence: [email protected] 1Cheng Gong New City, School of Public Health, Kunming Medical University, 1168 Yu Hua Street Chun Rong Road, Kunming 650500, China Full list of author information is available at the end of the article

© 2012 Cai et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Only through understanding the major factors that contribute to smoking behavior can we hope to design and execute effective tobacco control policies. There is growing evidence that patterns of smoking are related to age, sex, socioeconomic status (SES), and health risk be- havior [6-8]. People who are less educated, who earn less, and who are unemployed show higher prevalence rates of smoking in developed countries. An inverse rela- tionship between educational attainment and the risks of environmental tobacco exposure was also identified in previous Chinese and Korean studies [9,10]. In China, several studies have examined the relationship between smoking and SES variables in the general adult Chinese population [10-12], and show an inverse association be- tween education and smoking. However, little data are available concerning the associations between SES vari- ables and tobacco use in the Chinese tobacco-cultivating adult population. It is crucial that we understand the socioeconomic factors related to tobacco use and iden- tify target populations for tobacco control. Furthermore, the epidemiological studies conducted in China have fo- cused mostly on urban areas or national-level data, but the literature is still sparse in tobacco-cultivating rural areas, where the rate of tobacco consumption is the highest. The aim of this study is to describe the patterns and

socioeconomic influences of tobacco use among south- west China’s tobacco-cultivating rural adult population from 2010 to 2011.

Methods Study region This study used a community-based cross-sectional sur- vey and was conducted in two tobacco-cultivating rural areas of Yunnan Province in southwest China. In 2010, Yunnan Province had 129 official counties and a total population of 45.9 million people. It is a relatively un- developed province, and is a production and consump- tion hub for tobacco products. Roughly 70% of Yunnan Province’s annual tax revenue is collected from the tobacco industry, and tobacco is cultivated in 45 of the province’s counties [10]. Yunnan also has the country’s largest concentration of ethnic minorities, with 25 of China’s 56 state-recognized ethnicities living in the re- gion. For decades, the regional government of Yunnan has depended on the economic engine of tobacco. As a result, the strong enforcement of existing tobacco con- trol laws is not fully supported by the Yunnan govern- ment. The progress on tobacco control is not moving quickly in this region. More recently, Yunnan govern- ment implemented the anti-tobacco policy to prohibit smoking in public institutions including hospitals, healthcare centers and schools.

Sampling Multi-stage stratified random sampling was used to se- lect the study sample. In the first stage, all of Yunnan Provinces’ tobaccos cultivating counties were classified into two groups according to wealth distribution (per capita Gross Domestic Product): economically advan- taged (<$600) and economically disadvantaged (≥$600) based on the 2010 Yunnan Statistical Yearbook [13]. In order to guarantee the representativeness of each group, one county was randomly selected from each of these two economic groups. In the second stage, all township districts were selected for study in the two chosen coun- ties, for a total of 21 townships. In the third stage, three villages were chosen by probability proportional to size (PPS) from each of the 21 townships. In the final stage, in each selected village, we first obtained a list of names of individuals aged ≥ 18 years from the village commit- tee, and then simple random sampling was done with random number tables to select the individuals from this village.

Data collection and measurement Ten 5th-year medical students and twenty master degree students from Kunming Medical University were selected and extensively trained as interviewers for data collection. A workshop was held before the fieldwork to teach interviewers how to administer the screening questionnaire, and how to take blood pressure and an- thropometric measurements. Each participant was given a full explanation of the research purpose and invited to participate; signed informed consent; and was personally interviewed by one of the interviewers using a pre-tested structured questionnaire. The questionnaire asked for demographic characteristics, individual SES, ethnicity, household income, educational level, lifestyle factors such as alcohol consumption, self-reported smoking habits, exposure to SHS at home or work, and tobacco use-related health status.

Ethical approval This study was approved by the Ethics Committee of Kunming Medical University.

Definitions Current smoker was defined as a person who currently smoked any kind of tobacco product on a daily basis at the time of the survey. Exposure to SHS was defined as non-smokers who reported exposure to environmental tobacco smoke at home or at work for a minimum of 15 minutes at least one day per week. The location of ex- posure to SHS was defined as in the past seven days, the locations where others have smoked in front of a current smoker. Current drinker was defined as a person who drank alcohol regularly on 12 or more days during the

Cai et al. BMC Public Health 2012, 12:842 Page 2 of 8 http://www.biomedcentral.com/1471-2458/12/842

past 12 months. Self-reported current smokers were assessed for nicotine dependence using six questions from the Fagerstrom Test for Nicotine Dependence (FTND) [14]. The FTND has 6 items with an overall score ranging between 0–10. Very high dependence was defined as an FTND score ranging between 8–10; high dependence, a score between 6–7; medium dependence, a score equal to 5; low dependence, a score between 3– 4; and very low dependence, a score between 0–2.

Statistical analysis Descriptive analysis techniques, chi-squared test, and multivariate logistic regression were used in this study. Yearly household income was classified into three cat- egories: low (<$150 USD), medium ($150-600 USD), and high (>$600 USD). Categorical variables were presented as counts and percentages, and 95% confidence intervals (95% CI) for percentages were calculated according to the method described by Newcombe [15]. The sampling weights were calculated based on data from the year 2000 Yunnan Provincial Population Census and our sampling scheme. The prevalence of current smoking, nicotine dependence and exposure to SHS, however, were estimated based on weighted proportions. Chi- squared test was used to determine the percentage dif- ferences between men and women. Logistic regression was used to analyze the association between individual SES variables and the weighted prevalence of current smoking, intensity of smoking, exposure to SHS, and nicotine dependence. Associations were expressed as odds ratios and 95% CI. All statistical significance deci- sions were based on a two-tailed P value of <0.05. Due to large differences in smoking behavior between men and women, interactions were tested to determine whether SES variables varied by sex. All data analyses were conducted with R2.9.1 software [14].

Results A total of 8,800 individuals aged ≥18 years were invited to participate in this study. Of these, 8,681 agreed to participate (response rate = 98.6%). As shown in Table 1, the study population included

4,068 males and 4,631 females, 22.3% of which belonged to an ethnic minority, and 77.7% of which were Han Chinese. The proportion of participants who engaged in tobacco cultivation was 28.1%. Male participants had higher educational level than female participants (P<0.05). Table 2 describes weighted prevalence of current smo-

kers, nicotine dependence, and exposure to SHS by age, sex and tobacco-cultivating status among southwest Chi- na’s rural adult population. The overall prevalence rates of current smokers and exposure to SHS were 33.7% and 74.2% respectively, and the rate of nicotine

dependence among smokers was 84.8%. In general, men reported much higher rates of smoking and nicotine de- pendence than women (P<0.01), whereas women reported higher rate of exposure to SHS than men (P<0.05). The highest rates of current smokers, exposure to SHS, and nicotine dependence were found among individuals aged 35–44 years. Individuals who cultivated tobacco had higher prevalence rates of current smoking, exposure to SHS, and nicotine dependence than non- tobacco cultivating people (P<0.01). Table 3 displays patterns of tobacco exposure among

study participants. Filtered cigarette smoking was the most popular form of smoking tobacco, comprising 66.5% of all forms of tobacco consumed, followed by Hookah / Water pipe (57.7%). However, there were im- portant differences in these findings by sex. Filtered cigarette smoking was the most popular form of smok- ing tobacco for men, whereas hookah / Water pipe was the most popular form of smoking tobacco for women. Age of smoking initiation occurred mostly during ado- lescence (84.5%). 51.9% of current smokers reported daily smoking of more than 10 cigarettes. A total of 6.8% of current smokers were highly nicotine addicted. In the 12 months before the survey, only 13.2% of smokers tried at least one attempt to quit smoking. In the past seven days, 81.1% of smokers smoked in public places

Table 1 Demographic characteristics of the study population

Characteristics (%)

Male (n=4068)

Female (n=4613)

All (n=8681)

Age

18-34 years 1078 (26.5) 1099 (23.8) 2177 (25.1)

35-44 years 864 (21.2) 923 (20.0) 1787 (20.6)

45-54 years 702 (17.3) 850 (18.4) 1552 (17.9)

55-64 years 666 (16.4) 843 (18.3) 1509 (17.4)

≥65 years 758 (18.6) 898 (19.5) 1656 (19.1)

Tobacco cultivating

Yes 1267 (31.1) 1176 (25.5) 2443 (28.1)

No 2801 (68.9) 3437 (74.5) 6238 (71.9)

Ethnicity

Han 3226 (79.3) 3516 (76.2) 6742 (77.7)

Minorities 842 (20.7) 1097 (23.8) 1939 (22.3)

Level of education

Primary (grade 1–6) or lower 3402 (83.6)* 4107 (89.0)* 7509 (86.5)

Middle ((grade 7–9) or higher 666 (16.4) 506 (11.0) 1172 (13.5)

Level of yearly household income†

Low 856 (21.0) 1096 (23.8) 1952 (22.5)

Medium 2285 (56.2) 2701 (58.6) 4986 (57.4)

High 927 (22.8) 816 (17.7) 1743 (20.1)

* P<0.05 from chi-squared test for difference between sexes. † Low income is < $150 USD; medium is $150-600 USD; and high income is >$600.

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Table 2 Weighted prevalence of current smoking, nicotine dependence, and secondhand smoke (SHS) by age, sex and status of tobacco cultivation

Characteristics Prevalence of current smokers

Prevalence of nicotine dependence among smokers

Prevalence of SHS among non-smokers

Men Women All Men Women All Men Women All

% (95% CI)

% (95% CI)

% (95% CI)

% of smokers (95% CI)

% of smokers (95% CI)

% of smokers (95% CI)

% of non-smokers (95% CI)

% of non-smokers (95% CI)

% of non-smokers (95% CI)

Age

18-34 years 63.3 (60.3-66.0) 0.5 (0.1-0.8) 31.3 (29.5-33.9) 82.0 (79.8-85.5) 48.8 (9.45-90.6) 82.3 (58.6-86.0) 70.8 (65.6-74.6) 76.9 (74.9-79.9) 74.7 (73.4-77.7)

35-44 years 76.7 (73.7-79.3) 0.9 (0.2-1.0) 37.5 (35.1-40.6) 86.1 (83.6-88.8) 74.6 (30.1-95.4) 87.0 (64.2-90.3) 73.0 (65.7-78.0) 80.1 (78.1-83.2) 78.7 (76.7-81.5)

45-54 years 74.0 (70.9-77.3) 1.0 (0.6-2.1) 34.4 (31.8-36.5) 88.1 (84.2-89.9) 89.3 (56.5-98.0) 87.8 (78.3-96.2) 70.2 (63.7-76.9) 81.3 (77.9-84.3) 80.1 (76.4-82.4)

55-64 years 70.1 (66.1-73.0) 1.1 (0.4-1.6) 31.0 (28.9-33.6) 84.9 (81.8-88.3) 85.4 (48.7-97.4) 85.2 (68.2-94.7) 68.8 (59.1-74.0) 77.3 (73.1-79.9) 75.4 (71.3-77.7)

≥65 years 59.0 (56.1-63.1) 1.6 (1.0-2.8) 28.4 (26.1-30.4) 83.8 (80.7-87.4) 58.7 (35.8-80.2) 83.5 (67.1-83.5) 67.2 (65.9-76.0) 64.1 (62.0-68.3) 65.3 (64.1-69.4)

Tobacco cultivating

Yes 78.0 (75.1-79.7) 1.7 (0.5-1.7) 43.0 (38.7-45.6) 89.1 (86.5-91.4) 89.2 (59.6-98.2) 89.0 (84.5-90.4) 82.3 (77.2-86.1) 86.0 (83.3-87.8) 85.1 (82.9-87.6)

No 63.9 (62.4-65.9) 0.7 (0.6-1.2) 28.9 (28.2-30.4) 82.7 (81.4-84.9) 67.1 (47.8-81.4) 82.8 (81.0-84.7) 66.2 (63.8-69.7) 72.1 (71.4-74.4) 70.6 (69.2-72.8)

All 68.5 (66.9-69.7) 1.3 (0.8-1.6) 33.7 (31.5-35.5) 85.2 (83.7-86.4) 72.7 (57.0-84.6) 84.8 (83.1-86.3) 70.5 (67.6-72.6) 76.6 (74.8-77.8) 74.2 (73.1-75.9)

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(82.0% for men, and 16.2% for women); 77.6% smoked in workplace (78.3% for men, and 27.0% for women); 33.9% smoked in front of a pregnant woman (40.2% for men, and 11.3% for women); and 84.6% smoked in front of children while in indoor places (82.1% for men, and 74.1% for women). We found no association between any SES indicators

and the intensity of smoking. Table 4 shows the results of logistic regression for prevalence of current smokers, nicotine dependence, and exposure to SHS after adjust- ing for possible confounders. After adjusting for age, sex, tobacco cultivation, drinking status, and type of county, as well as further adjusting for other measures of SES, individuals who belong to an ethnic minority had a lower probability of nicotine dependence and of being exposed to SHS. Individuals with higher levels of education had a lower probability of current smoking, ex- posure to SHS, and nicotine dependence. Furthermore,

higher yearly household incomes were found to be asso- ciated with a higher risk of nicotine dependence, but not with current smoking or SHS exposure. Individuals who cultivated tobacco had a higher probability of current smoking, exposure to SHS, and nicotine dependence. Although we tested for possible interactions, there were no significant interactions between sex and SES variables.

Discussion The findings indicate a high prevalence of smoking, and a high prevalence of exposure to SHS among non-smo- kers. There was also a high rate of SHS exposure among current smokers in public places, and a low rate of attempting to quit smoking among current smokers in rural southwest China. Individual SES was found to be independently associated with the prevalence of current smoking, exposure to SHS, and nicotine dependence.

Table 3 Patterns of tobacco exposure among current smokers in rural areas of Yunnan province, China

Variables Men (N=2780) Women (N=37) All (N=2817)

n (%) n (%) n (%)

Use of various forms of tobacco+

Filtered cigarettes 1718 (61.8) 16 (43.2) 1734 (61.6)

Hookah / Water pipe 1447 (52.1) 22 (59.5) 1469 (52.1)

Pipe tobacco 137 (4.9) 5 (13.5) 142 (5.0)

Hand-rolled cigarettes 137 (4.9) 1 (2.7) 138 (4.9)

Unfiltered cigarettes 103 (3.7) 0 (0.0) 103 (3.7)

Chewing tobacco 31 (1.1) 0 (0.0) 31 (1.1)

Age of smoking initiation

<=11 years 97 (3.5) 2 (5.4) 99 (3.5)

12-20 years 2257 (81.2) 26 (70.2) 2283 (81.0)

21-34 years 405 (14.6) 5 (13.5) 410 (14.6)

>=35 years 21 (0.8) 4 (10.8) 25 (0.9)

Previous quit attempts

At least one attempt in previous 12 months 368 (13.2)* 3 (8.1)* 371 (13.2)

No attempt 2412 (86.8) 34 (91.9) 2446 (86.8)

Amount of smoking per day (cigarettes)

<10 1323 (47.6)* 33 (89.2)* 1356 (48.1)

>=10 1457 (52.4) 4 (10.8) 1461 (51.9)

Nicotine dependence

High or very high dependence (score 6–10) 189 (6.8) 2 (5.4) 191 (6.8)

Medium dependence (score 5) 225 (8.1) 3 (8.1) 228 (8.1)

Low or very low dependence (score less than 5) 2366 (85.1) 32 (86.5) 2398 (85.1)

In the past seven days, the conditions under which others have smoked in front of you

Public spaces (schools, hospitals, etc.) 2280 (82.0)** 6 (16.2)** 2286 (81.1)

Workplace (labor field) 2176 (78.3)** 10 (27.0)** 2186 (77.6)

In front of a pregnant woman while in indoor places ++ 331 (40.2)** 2 (11.3)** 351 (33.9)

In front of children while in indoor places +++ 1657 (82.1) 20 (74.1) 1677 (84.6)

* P<0.05 from chi-squared test for difference between sexes, ** P<0.01 from chi-squared test for difference between sexes, † The current smoker used more than one form of smoking tobacco, †† The denominator is the number of current smokers living with children at home, ††† The denominator is the number of current smokers living with pregnant woman at home.

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It has been estimated that worldwide, men smoke more than women. Our finding is in concordance with other studies [16]. In this study, the prevalence of smoking among men was greater than the preva- lence rate observed in 2010 China Global Adults Tobacco Survey (GATS, 56.1%) [17], other parts of rural China (66.8%) [10], adults from western coun- tries [7,8], and other Asian and African people [18- 20]. Smoking has been very prevalent in the Chinese tobacco cultivating rural male population. In contrast to the high prevalence of smoking, our study reported a low prevalence of smokers who have pre- viously attempted to quit smoking (18.2%), a rate that was much lower than reported by the 2010 China GATS survey (33.1%), in other cities of China (25.3%) [21], and in other western countries (40%) [22]. These data indicate that rural communities are in need of robust smoking cessation programs. Several previous Chinese studies indicate that most

Chinese smokers initiate smoking during adolescence, and the prevalence of adolescent smoking has been in- creasing rapidly in China [23,24]. Our study is consistent with these prior studies, and demonstrates that over 80% of smokers start smoking during adolescence. These findings underscore an urgent need for tobacco control strategies in rural China for adolescents and young adults who are at high risk for becoming addicted to nicotine. As shown in other Chinese studies, smoking cigarettes

was the most popular form of tobacco use in rural southwest China [10,25]. Furthermore, we found that consuming tobacco through hookah / water pipes was also common in the tobacco–cultivating, ethnically di- verse, rural communities. Our findings indicate that cul- tural forces exert a strong effect on smoking habits, as has been demonstrated in previous studies [26].

Our study showed a high rate of exposure to SHS among current smokers, particularly in public places. The rate of exposure to SHS in public places observed in this study (81.1%) is much higher than the China na- tional survey results of 2002 (67.0%) [3], as well as results from another Chinese study (72.7%) [27], indicat- ing public places have become the worst places for SHS exposure in rural southwest China. Furthermore, our study showed that exposure to SHS among current smo- kers in households mostly occurred in front of children and pregnant women. While smoking among women in the study region was at a much lower level compared with men, over 75% of women were exposed to SHS, and the rate of exposure to SHS among women was higher than among men, indicating exposure to SHS is a serious health problem for women. The impact of SHS exposure on children’s and women’s health requires ur- gent attention. Evidence has shown that the implementa- tion of comprehensive smoke-free policies decreases the exposure to SHS and its associated health hazards in non-smokers [28]. These results suggest it is essential to strengthen people’s awareness of tobacco hazards and to implement comprehensive smoke-free laws and legisla- tions to protect people from SHS. Our study found individuals who cultivated tobacco

had higher prevalence rates of current smoking, expos- ure to SHS, and nicotine dependence than non-tobacco- cultivating people. This is possibly due to tobacco farm- ers having easier access to tobacco products. These results suggest tobacco cultivating status is an important consideration when developing tobacco control policies in rural China. Ethnic minorities had a lower risk for exposure to SHS

and nicotine dependence in this study. Genetic heritabil- ity and shared environmental influences have been reported to be related to cigarette smoking in a previous

Table 4 Weighted Logistic regression coefficients for current smoking, nicotine dependence and exposure to secondhand smoke (SHS) by ethnicity and socioeconomic status

Variables Current smokers Nicotine dependence SHS

(N=8681) (N=8681) (N=8681)

Adjusted odds ratio† 95% CI Adjusted odds ratio† 95% CI Adjusted odds ratio† 95% CI

Ethnicity (reference: Han)

Minorities 0.93 (0.79, 1.10) 0.79** (0.69, 0.95) 0.84** (0.74, 0.95)

Level of education (reference: primary (grade 1–6) or lower)

Middle (grade 7–9) or higher 0.63** (0.51, 0.78) 0.56** (0.46, 0.65) 0.51** (0.43, 0.61)

Level of yearly household income (reference: Low)

Medium 1.08 (0.97, 1.20) 1.16* (1.04, 1.31) 1.06 (0.93, 1.11)

High 1.05 (0.93, 1.18) 1.11* (1.02, 1.19) 1.00 (0.90, 1.06)

Tobacco cultivating (reference: no)

Yes 3.18** (2.77, 3.65) 2.42** (2.12, 2.77) 1.35** (1.17, 1.55)

* p<0.05, ** p<0.01, † adjusted for age, sex, and alcohol drinking.

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study [29]. This finding suggests that ethnicity is an im- portant determinant for tobacco use. Lower levels of education have been shown to be asso-

ciated with higher risks of smoking, environmental tobacco exposure, nicotine dependence, and lower rates of quitting tobacco use, both in developed and develop- ing countries [8,9,30]. In the present study, smoking, ex- posure to SHS, and nicotine dependence tended to be more prevalent in people who were less educated. Our result is in concordance with prior studies. Some previ- ous Chinese studies also indicated an inverse association between education and smoking [2,11,12,18]. Our find- ings suggest community-based tobacco control efforts need to increase the knowledge related to harm of tobacco use among people with low levels of education. While several western studies have demonstrated that

people with lower incomes are more likely to consume tobacco [6-9], our study showed no association between individual income and smoking or exposure to SHS in the Chinese rural adults. However, it did show a positive relationship between individual income and nicotine de- pendence. A previous Chinese study reported that people with higher annual income were more likely to smoke than those with lower income [18]. The reasons for an inconsistent association between income and smoking rates in Chinese adult smokers are unknown. A strength of our study is the large sample size and

the high response rate (over 98%) in the community sur- vey. A limitation of the study is that smoking was self- reported and exposure to SES was based on recall. The lack of validation of smoking status with nicotine testing may underestimate the prevalence of smoking.

Conclusion In conclusion, smoking and exposure to SHS are very prevalent in rural southwest China. The results of this study suggest that future tobacco control efforts and policies should focus more on people who cultivate tobacco, who are less educated, and who belong to the Han majority.

Competing interests The authors declare that they have no conflicts of interest.

Authors’ contributions CL carried out the study and drafted and revised the manuscript. WX and HY participated in the design of the study. AG participated in the design of the study and helped to revise the manuscript. CW, XX, HJ, ZK, SY, and JF collected the data. All authors read and approved the final manuscript.

Acknowledgements We would like to thank Dr. Jia Shen from Emory University for her review and helpful comments regarding the manuscript. This publication is based on research funded by the Bill & Melinda Gates Foundation. The findings and conclusions contained within are those of the authors and do not necessarily reflect the positions or policies of the Bill & Melinda Gates Foundation.

Author details 1Cheng Gong New City, School of Public Health, Kunming Medical University, 1168 Yu Hua Street Chun Rong Road, Kunming 650500, China. 2Emory University, Atlanta, GA 30322, USA.

Received: 22 March 2012 Accepted: 2 October 2012 Published: 4 October 2012

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doi:10.1186/1471-2458-12-842 Cite this article as: Cai et al.: Patterns and socioeconomic influences of tobacco exposure in tobacco cultivating rural areas of Yunnan Province, China. BMC Public Health 2012 12:842.

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