Household environmental tobacco smoke exposure, respiratory symptoms and asthma in non-smoker adults: a multicentric population study from India.

BACKGROUND: Exposure to environmental tobacco smoke (ETS) is a risk factor for childhood asthma. Its association with asthma in adults is less clear.
METHODS: In a multicentric population study on asthma prevalence in adults, specific enquiries were made into childhood and adulthood exposure to household ETS, and its relationship with asthma diagnosis were analysed.
RESULTS: From a total of 73605 respondents, 62109 were studied after excluding current or past smokers. Overall observed prevalence of asthma was 2.0% (men 1.5%,women 2.5%, p < 0.001). Of all asthma patients, history of ETS exposure was available in 48.6 percent. Prevalence of asthma in the ETS exposed subjects was higher compared to non-exposed individuals (2.2% vs 1.9%, p < 0.05). Multiple logistic regression analysis showed a higher risk of having asthma in persons who were exposed to ETS compared to those not exposed (odds ratio [OR] 1.22, 95% CI 1.08-1.38) after adjusting for age, gender, usual residence, exposure to biomass fuels and atopy. Stratification of ETS exposure revealed that exposure during childhood and both during childhood and adulthood were significantly associated with asthma prevalence. Exposure only in adulthood was not a significant risk factor (OR 1.13, 95% CI 0.95-1.33). Persons reporting combined environmental tobacco smoke exposure from parents during childhood and spouse during adulthood had highest risk of having asthma (OR 1.69, 95% CI 1.38-2.07). Environmental tobacco smoke exposure was also significantly associated with prevalence of respiratory symptoms such as wheezing, cough and breathlessness.
CONCLUSIONS: Environmental tobacco smoke exposure during childhood is an important risk factor for asthma and respiratory symptoms in non-smoking adults.