Exposure to Secondhand Smoke Among Students Aged 13--15 Years --- Worldwide, 2000--2007

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Breathing secondhand smoke (SHS) causes heart disease and lung cancer in adults and increased risks for sudden infant death syndrome, acute respiratory infections, middle-ear disease, worsened asthma, respiratory symptoms, and slowed lung growth in children (1--3). No risk-free level of exposure to SHS exists (1). The Global Youth Tobacco Survey (GYTS), initiated in 1999 by the World Health Organization (WHO), the Canadian Public Health Association, and CDC includes questions related to tobacco use, including exposure to SHS (4).* This report examines data collected from 137 jurisdictions (i.e., countries and territories) during 2000--2007, presents estimates of exposure to SHS at home and in places other than the home among students aged 13--15 years who had never smoked, and examines the association between exposure to SHS and susceptibility to initiating smoking.^§ GYTS data indicated that nearly half of never smokers were exposed to SHS at home (46.8%), and a similar percentage were exposed in places other than the home (47.8%). Never smokers exposed to SHS at home were 1.4--2.1 times more likely to be susceptible to initiating smoking than those not exposed. Students exposed to SHS in places other than the home were 1.3--1.8 times more likely to be susceptible to initiating smoking than those not exposed. As part of their comprehensive tobacco-control programs, countries should take measures to create smoke-free environments in all indoor public places and workplaces.

GYTS is a school-based survey that collects data from students by using a standardized methodology for constructing the sample frame, selecting participating schools and classes, and processing data (4). Questionnaires were translated by coordinators into local languages and back-translated to check for accuracy; GYTS country research coordinators chaired focus groups of students aged 13--15 years to further test the translation accuracy and question comprehension. A two-stage, cluster-sample design was used to produce representative samples of students attending public and private schools in grades associated with ages 13--15 years in each country at national, regional, or local levels. A weighting factor was applied to each student record to adjust for nonresponse by school, class, and student and for variation in the probability of selection at the school and class levels. A final adjustment summed the weights by grade and sex to the population of school children in the selected grades in each country sample site. Statistical analysis of correlated data was conducted, and standard errors of the estimates were computed, producing 95% confidence intervals (CIs). Data included in this report were from GYTS surveys conducted in 137 jurisdictions during 2000--2007. Nationally representative data were collected in 105 jurisdictions, and subnational representative data were collected in 32 jurisdictions. In the 137 jurisdictions included in this study, 747,603 students in approximately 10,000 schools completed the GYTS. Of the jurisdictions surveyed, 56.5% had 100% school participation rates, 41.3% had rates of 80%--99%, and 2.2% had school participation rates of <80%. Approximately 40% of the jurisdictions had student response rates of >90%, 50.7% had rates of 80%--90%, and 9.3% had student response rates of <80%.

Data were aggregated within each of the six WHO regions (Africa, Americas, Eastern Mediterranean, Europe, South-East Asia, and Western Pacific). Self-reported exposure to SHS at home and in places other than home was assessed in the six WHO regions. Regional aggregations were calculated as means weighted by the population of the sampling frame. In many cases, the sampling frame was the country, but in areas where samples were drawn to represent a subnational population, estimates were weighted by the population of the city, state, or administrative region and included in the regional aggregation.

Never smokers were defined as students who responded "no" to the question "Have you ever smoked a cigarette, even one or two puffs?" Exposure to SHS was determined by answers to two questions: "During the past 7 days, on how many days have people smoked in your home, in your presence?" and "During the past 7 days, on how many days have people smoked in your presence, in places other than in your home?" Students who answered 1 or more days were considered exposed to SHS. Susceptibility to initiating smoking was determined by answers to two questions: "If one of your best friends offered you a cigarette would you smoke it?" and "At any time during the next 12 months do you think you will smoke a cigarette?" Students who answered "definitely not" to both questions were considered not susceptible to initiating smoking. Students who answered "definitely yes," "probably yes," or "probably no" to either question were considered susceptible to initiating smoking.

Overall, 80.3% of students aged 13--15 years said they had never smoked cigarettes, with the percentage ranging from 87.4% in the South-East Asia region to 54.9% in the Americas (Table). The percentage of never smokers exposed to SHS at home was 46.8% and ranged from 71.5% in Europe to 22.6% in Africa. Among WHO regions, never smokers exposed to SHS at home were 1.4--2.1 times more likely to be susceptible to initiating smoking than those not exposed (Table). The percentage of students exposed to SHS in places other than home was 47.8% overall and ranged from 79.4% in Europe to 38.2% in Africa. By region, never smokers exposed to SHS in places other than home were 1.3--1.8 times more likely to be susceptible to initiating smoking than those not exposed.

Reported by: DW Bettcher, MD, PhD, A Peruga, MD, DrPH, Tobacco Free Initiative, Geneva, Switzerland; B Fishburn, MPP, Western Pacific Regional Office; J Baptiste, PhD, African Regional Office; F El-Awa, PhD, Eastern Mediterranean Regional Office; H Nikogosian, MD, European Regional Office; K Rahman, PhD, South-East Asia Regional Office; V Costa de Silva, MD, PhD, Region of the Americas, World Health Organization, Geneva, Switzerland. J Chauvin, Canadian Public Health Association, Ottawa, Canada. CW Warren, PhD, NR Jones, PhD, J Lee, MPH, V Lea, MPH, M Lewis, MPH, S Babb, MPH, S Asma, DDS, MT McKenna, MD, Office on Smoking and Health, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note:

In a longitudinal study of factors predicting smoking behavior of adolescents, having parents and best friends who smoked increased the likelihood that a never smoker would initiate smoking (5). Exposure to SHS is a recognized factor associated with susceptibility to initiating smoking among never smokers. Before development and implementation of GYTS, few global data existed on the use of tobacco products or factors associated with tobacco use among adolescents (4). This study determined that students who were never smokers and exposed to SHS at home and in places other than the home were more likely to be susceptible to initiating smoking than those not exposed. This finding was consistent across all six WHO regions, although with small variations in the size of the ratio between those exposed to SHS and those not exposed. Also, data on susceptibility were consistent over the years of study, both within country (i.e., in repeat surveys) and within region.

The association between susceptibility and SHS exposure is consistent with a previous report based on GYTS data. That report concluded that unless tobacco consumption and exposure to SHS are reduced, the global burden of disease attributable to tobacco will continue to increase (4). To protect the health of all persons from the harmful effects of SHS, WHO recommends that countries enact and enforce legislation requiring all indoor workplaces and public places to be 100% smoke-free (6). Further, WHO suggests that countries develop and implement educational strategies to reduce SHS exposure in the home.

The findings in this report are subject to at least three limitations. First, because GYTS is limited to students, the survey might not be representative of all youths aged 13--15 years from participating countries. However, in most countries, the majority of persons in this age group attend regular, private, or technical schools (7). Second, these data apply only to youths who were in school on the day of the survey and who completed the survey. However, student response rates were high (more than 90% of the sites had student response rates of 80% or higher), suggesting that bias attributable to absence or nonresponse was limited. Finally, data were based on the self-report of students, who might underreport or overreport their behaviors or attitudes. The extent of this bias cannot be determined from these data; however, reliability studies in the United States have indicated good test-retest results for similar tobacco-related questions (8).

Scientific evidence has determined that a safe level of exposure to SHS does not exist; SHS is a pollutant that causes serious illnesses in adults and children (1--3). Therefore, implementing 100% smoke-free environments is the only effective way to protect the population from exposure to SHS. Article 8 of WHO's Framework Convention on Tobacco Control, ratified by more than 145 countries, calls for jurisdictions to provide "protection from exposure to tobacco smoke in indoor workplaces, public transport, indoor public places and, as appropriate, other public places" (9).

In 2004, Ireland became the first nation to create smoke-free indoor workplaces and public areas with a comprehensive ban that included restaurants, bars, and pubs. Since then, bans have been enacted in other countries: Italy, Mauritius, New Zealand, Niger, Norway, Uganda, United Kingdom (in Northern Ireland, Scotland, and Wales), and Uruguay (6). In Canada, 80% of the population lives in jurisdictions with comprehensive smoke-free legislation (6). The majority of persons in the United States live under a state or local law that makes workplaces, restaurants, or bars completely smoke-free: 23.8% of the population is covered by laws that make all three settings smoke-free, and 38.8% of the population is covered by laws that make workplaces smoke-free (10).

The goal of WHO's 2007 World No Tobacco Day is to promote smoke-free environments. Such policies will reduce mortality among nonsmokers who die from diseases caused by breathing SHS and tobacco use among persons who continue to smoke (6).

References

The number of jurisdictions varied by year. Some jurisdictions conducted repeat surveys; for those jurisdictions, the most recent data were used. Following are the number of jurisdictions from which data were collected, by year: 2000, six; 2001, nine; 2002, 21; 2003, 36; 2004, 25; 2005, 19; 2006, 15; and 2007, six.

^§ The Teenage Attitudes and Practices Survey, a follow-up study to the National Health Interview Survey, was conducted in 1989 and 1993 and determined that youths defined as susceptible to initiating smoking were two to three times more likely to initiate smoking than nonsusceptible youths. To be classified as nonsusceptible to smoking, a respondent had to answer "no" to the question, "Do you think that you will try a cigarette soon?" and "definitely not" to the questions, "If one of your best friends were to offer you a cigarette, would you smoke it?" and "Do you think you will be smoking cigarettes 1 year from now?" (5).

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