Exposure to second-hand smoke: a population-based survey in Spain

To the Editors:

In 1972, a US Surgeon General’s report, “The Health Consequences of Smoking”, addressed the topic of passive smoking 1. More than three decades later, another Surgeon General’s report, “The Health Consequences of Involuntary Exposure to Tobacco Smoke”, concluded that a causal relationship exists between second-hand smoke (SHS) exposure experienced by lifelong nonsmokers and several diseases, including lung cancer and coronary heart disease 2.

Despite the report's findings, legislation promoting population protection against this ambient carcinogen 3 has been slow to take hold globally. The exposure of the Spanish population remains unknown and existing data on prevalence of exposure is limited to selected areas or specific populations 4, 5. An anti-smoking law was recently implemented in Spain 6, with the aim of combating this health problem by decreasing population exposure to SHS in employment and public settings.

Between December 2004 and January 2005, we developed a study on tobacco use and SHS exposure among the general population in the northern Spanish region of Galicia. The source of sampling was the regional healthcare card system, which covers 97% of the population. The study yielded SHS exposure data collected in Galicia, based on a representative population sample. Galicia is located in the north-west of Spain and was estimated to have a population of 2.7 million in 2004, with a smoking prevalence of 29% (95% confidence interval 27.8–30.2%). People who smoked daily or occasionally were classified as smokers.

One of the study's objectives was to estimate exposure to SHS in the general population, aged 16–74 yrs. The sampling unit was the individual and the sample (n = 6,492) was representative by sex and was divided into age groups: 16–24, 25–44, and 45–74 yrs. Data collection was carried out primarily through telephone interviews (90%); however, 10% of the interviews were conducted in person, in order to avoid under-representation of people without phone facilities.

The Galician Smoking Interview Survey included several questions that aimed to estimate SHS exposure within the three microenvironments most commonly frequented by the population: work, house, and public places. Questions referred to the week prior to the interview.

Results indicate that 74.6% (73.2–75.9%) of the Galician population were exposed to SHS: 80.5% (79.0–82.1%) of males and 68.2% (66.1–70.4%) of females. More detailed results are shown in table 1⇓.

The Barcelona Health Interview Survey 2000, a study developed in Spain applying similar measures of SHS exposure, yielded similar results. A 69.7% prevalence of SHS exposure was found in an urban population aged 15–64 yrs, taking into consideration exposure at home and work. In the USA, where restrictive laws for decreasing exposure to SHS preceded similar laws in Spain, the prevalence of exposure was lower (∼40% in adults) 2.

Taking into consideration all biases related to second-hand smoke exposure measurement using questionnaires, as well as acceptable agreement with levels of cotinine 7 and the fact that self-declared exposure often underestimates actual exposure 8, the problem is likely to be even more troublesome than this study indicates. These results prove that second-hand smoke poses an important public health problem in Galicia.