Who is exposed to smoke at home? A population-based cross-sectional survey in central Vietnam.

Secondhand smoke (SHS) exposure is an important global health issue.1 2 The World Health Organization Framework Convention on Tobacco Control (WHO FCTC) obligates countries to protect people from SHS exposure in public places such as workplaces and public transport, whereas protection measures from SHS in the home are not addressed explicitly.3 The objective of this study was to investigate the prevalence of domestic SHS exposure and sociodemographical risk factors associated with SHS among a population in central Vietnam.

A dataset from population-based cross-sectional survey conducted in Khanh Hoa Province, central Vietnam, was analysed. The original survey was carried out from June to July 2006 for the purpose of collecting information on possible risk factors of childhood diseases. Data on 353 525 residents living in 75 828 households were collected from occupants. Householders were queried about each household member's smoking habit during structured interviews. To identify participants who smoked and household members of smokers who were exposed to secondhand smoke, interviewers asked, “Does s/he smoke? (yes/no) If yes, does s/he usually smoke inside home? (yes/no)”. Detailed methods and characteristics of study population have been described previously.4 Residents were classified by smoking status as indoor smoking, non-indoor smoking and non-smoking. SHS exposure at home was defined as living with one or more indoor smokers. Age was categorised by decades into eight groups and household wealth levels were divided into quintiles according to the asset index (numbers of population by sex and age group are shown in the supplementary material). To assess the association between SHS exposure status and sociodemographic risk factors, simple tabulation and logistic regression analysis were performed. In order to take into account intracommune clustering, a multilevel analysis with a random intercept was applied to each model. The statistical software package R 2.8.1 (http://www.r-project.org/) was used for all analyses.

Among all residents in the study population, 60 608 (17.1%) were current smokers and 58 929 (97.2% of smokers) were men. Among all current smokers, 54 893 (90.6% of smokers) smoked indoors (figure 1). Among 292 917 non-smokers, 167 298 (57.1%) were exposed to smoke at home (table 1). In multiple logistic regression analysis, women (adjusted OR (AOR) 1.75, 95% CI 1.72 to 1.78) and children (for aged 0 to 9 years vs aged 40 to 49 years, AOR 2.05, 95% CI 1.99 to 2.12; for aged 10 to 19 years vs aged 40 to 49 years, AOR 2.02, 95% CI 1.96 to 2.08) were at increased risk of domestic SHS exposure (table 1).

Figure 1

The prevalence of smoking and domestic secondhand smoke exposure by sex and 10-year age group in Khanh Hoa Province, Vietnam, 2006.

Table 1

The prevalence and sociodemographical risk factors for domestic secondhand smoke exposure among non-smokers in Khanh Hoa Province, Vietnam, 2006

Characteristic	Total (%), n=292917	SHS* exposed (%), n=167298	UOR† (95% CI)	p Value	AOR‡ (95% CI)	p Value
Sex
Female	177702 (60.7)	107732 (60.6)	1.43 (1.41 to 1.45)	<0.0001	1.75 (1.72 to 1.78)	<0.0001
Male	115215 (39.3)	59566 (51.7)	1		1
Age, years
0–9	53669 (18.3)	34511 (64.3)	1.97 (1.91 to 2.03)	<0.0001	2.05 (1.99 to 2.12)	<0.0001
10–19	75332 (25.7)	49024 (65.1)	1.98 (1.92 to 2.03)	<0.0001	2.02 (1.96 to 2.08)	<0.0001
20–29	48876 (16.7)	28199 (57.7)	1.54 (1.49 to 1.58)	<0.0001	1.48 (1.43 to 1.53)	<0.0001
30–39	42777 (14.6)	21837 (51.1)	1.20 (1.17 to 1.24)	<0.0001	1.16 (1.13 to 1.20)	<0.0001
40–49	32161 (11.0)	14719 (45.8)	1		1
50–59	16905 (5.8)	7994 (47.3)	1.01 (0.97 to 1.05)	0.62	1.02 (0.98 to 1.06)	0.35
60–69	11066 (3.8)	5355 (48.4)	0.99 (0.95 to 1.04)	0.70	1.02 (0.97 to 1.07)	0.44
≥70	12131 (4.1)	5659 (46.7)	0.91 (0.87 to 0.96)	0.0001	0.98 (0.93 to 1.02)	0.33
Number of household members
<4	39760 (13.6)	12027 (30.3)	1		1
4–5	129650 (44.3)	71782 (55.4)	2.97 (2.90 to 3.05)	<0.0001	2.81 (2.74 to 2.89)	<0.0001
6–8	90658 (31.0)	60971 (67.3)	4.77 (4.64 to 4.90)	<0.0001	4.57 (4.44 to 4.69)	<0.0001
>8	32849 (11.2)	22518 (68.6)	6.18 (5.97 to 6.39)	<0.0001	5.91 (5.71 to 6.12)	<0.0001
Wealth level
Lowest fifth	72108 (24.6)	46052 (63.9)	1.53 (1.49 to 1.57)	<0.0001	1.64 (1.59 to 1.68)	<0.0001
Second fifth	55961 (19.1)	38514 (68.8)	2.07 (2.01 to 2.12)	<0.0001	2.03 (1.97 to 2.09)	<0.0001
Middle fifth	43159 (14.7)	25760 (59.7)	1.61 (1.57 to 1.65)	<0.0001	1.60 (1.55 to 1.65)	<0.0001
Fourth fifth	60368 (20.6)	32287 (53.5)	1.37 (1.34 to 1.40)	<0.0001	1.36 (1.32 to 1.39)	<0.0001
Highest fifth	61321 (20.9)	24685 (40.3)	1		1

Secondhand smoke.

Unadjusted OR.

Adjusted OR.

The prevalence of smoking was extremely high among adult men whereas the majority of domestic SHS victims were women and children in central Vietnam. Two factors may explain this finding. First, the prevalence of indoor smoking among smokers is high (90.6%). In Vietnam, smoking in public spaces is not banned except in healthcare facilities and indoor office buildings.5 Many smokers may not appreciate the health benefits of a smoke-free indoor environment. Second, the average household size in our study area (5.6) is much greater than that in developed countries such as USA (2.6 in 2006, US Census Bureau) and Japan (2.6 in 2005, Ministry of Internal Affairs and Communications). Thus, many non-smoking household members may share indoor environments with smokers.

The WHO FCTC is the first global public health treaty that the 166 WHO member states have already ratified.3 Article 8 of the WHO FCTC addresses the issue of protection from exposure to tobacco smoke in public places, however, there's no statement on protection from domestic SHS. Despite the lack of biological data, our results clearly indicate that SHS exposure occurs in public places and also in households. For women and children in particular, the household likely represents the primary location of exposure.6 Public educational campaigns for smoke-free homes7 8 are warranted in Southeast Asian countries, to protect women and children who remain exposed to SHS at home.