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Tobacco Smoking May Increase Risk for Tuberculosis

September 1, 2009 — Tobacco smoking is associated with a 2-fold increased risk for active tuberculosis, according to the results of a prospective Taiwan cohort study reported in the September 1 issue of the American Journal of Respiratory and Critical Care Medicine.

“Previous case-control studies and a small number of cohort studies in high-risk populations have found an association between tobacco and active tuberculosis, but no cohort studies have been conducted in the general population on this association to date,” write Hsien-Ho Lin, MD, ScD, from Harvard School of Public Health in Boston, Massachusetts, and colleagues.

The goal of the study was to evaluate the association between tobacco smoking and active tuberculosis in a general population cohort of 17,699 participants older than 12 years enrolled in the Taiwan National Health Interview Survey. An in-person interview at baseline determined smoking status and other covariates. During follow-up from 2001 to 2004, incident cases of active tuberculosis were identified with use of the National Health Insurance database. After adjustment for age, sex, alcohol intake, socioeconomic status, and other covariates, the association between smoking status and active tuberculosis was estimated with multivariate logistic regression.

During the 3.3 years of follow-up, there were 57 new cases of active tuberculosis. Current smoking was linked to an increased risk for active tuberculosis (adjusted odds ratio [OR], 1.94; 95% confidence interval, 1.01 – 3.73). Compared with patients older than 65 years, those younger than 65 years showed a stronger association between current smoking and the risk for active tuberculosis (adjusted OR, 3.04 vs 0.78; P for interaction = .036). There were significant dose-response associations for cigarettes per day (P for trend = .0036), years of smoking (P for trend = 0.023), and pack-years (P for trend = .0023).

“Tobacco smoking was associated with a twofold increased risk of active tuberculosis in a representative cohort of Taiwan’s population,” the study authors write. “The finding that smoking increases the risk of tuberculosis suggests that tobacco control be considered as an important component in the global effort to eliminate tuberculosis.”

Limitations of this study include deaths not recorded in the National Health Insurance database, short duration of follow-up, and lack of data from bacteriologic studies for the diagnosis of tuberculosis.

“Based on the results from our and other observational studies, policy makers and public health personnel should consider addressing tobacco cessation as part of TB [tuberculosis] control,” the study authors conclude. “Recent studies suggest that introducing brief tobacco cessation advice may be feasible among TB patients, and an integrated approach has been proposed to monitor smoking cessation in TB care. From the perspective of prevention, the target of smoking cessation should aim beyond TB patients to reach high-risk populations who are likely to benefit most from cessation.”

This study was supported by a grant from the World Bank through the International Union against Tuberculosis and Lung Disease and a fellowship from the Taiwan American Foundation of Boston. Some of the study authors have disclosed various financial relationships with Abt Associates, Bristol-Myers Squibb, and/or Pulmatrix.

Am J Respir Crit Care Med. 2009;180:475-480. Abstract

Clinical Context

Tuberculosis is among the leading causes of death from infectious diseases in the world. The World Health Organization has a goal to lower the incidence of tuberculosis to less than 1 case per million by 2050, so identifying and managing modifiable risk factors is a priority. An estimated 1.3 billion people worldwide smoke tobacco products, and a positive association has been shown between smoking and active tuberculosis, as well as mortality from tuberculosis based on case-control and cross-sectional studies. However, there has been a lack of longitudinal population-based studies demonstrating this association.

This is a prospective cohort study using Taiwan’s National Health Interview Survey to examine the association between tobacco smoking and the subsequent risk for tuberculosis at 3 years of follow-up. In Taiwan, the smoking rate is more than 40% among men and 4% among women.

Study Highlights

* A cohort of 17,699 patients from the National Health Interview Survey were observed from 2001 to 2004 and incident cases of active tuberculosis identified from the National Health Insurance database.
* The National Health Insurance database included 97% of Taiwan’s residents in 2001.
* At baseline, participant demographics, smoking behaviors, and other lifestyle factors were obtained by in-person interview.
* Data were available on the number of cigarettes smoked per day, years of smoking, age of onset of smoking, and exposure to secondhand smoke at home.
* Ever-smokers were defined as those who had smoked more than 100 cigarettes in their lifetime, current smokers as those who smoked within the past month, and former smokers as those who had not smoked in the past 1 month.
* Covariates examined included alcohol use, sex, income, marital status, employment, and indigenous community status.
* The primary outcome was active tuberculosis cases derived from the National Health Insurance database with use of International Classification of Diseases, Ninth Revision, Clinical Modification, codes plus prescription of more than 2 antituberculosis medications for more than 28 days.
* Overall among the participants, 3893 were current smokers, 552 were former smokers, and 13,254 were never-smokers.
* 40.0% of men and 4.2% of women smoked at baseline.
* Among current smokers, 22% were from low-income homes, 64% were married or cohabiting, 22% were regular alcohol drinkers, and 70% were employed.
* At baseline, median age was 39 years for current smokers, 57 years for former smokers, and 37 years for never-smokers.
* Active tuberculosis occurred in 24 current smokers, 3 former smokers, and 30 never-smokers.
* Compared with never smoking, the crude OR for incident tuberculosis for ever smoking and current smoking were 2.69 and 2.73, respectively.
* After adjustment for confounders, only current smoking was significantly associated with active tuberculosis, with an OR of 1.94.
* The association was affected by age.
* The risk for active tuberculosis with current smoking was higher for those 65 years and younger vs those older than 65 years (OR, 3.04 for the comparison).
* There was no effect of sex or living in an indigenous community on the risk for incident tuberculosis.
* Although the prevalence of tuberculosis was higher in men vs women, the OR for incident tuberculosis in men was not increased vs women once adjusted for current smoking.
* Thus, the authors postulated that the association between smoking and tuberculosis was not dependent on sex.
* The association between ever smoking and tuberculosis was not significant.
* Among current smokers, there was a significant linear dose-response association between the number of cigarettes smoked daily, years of smoking, and pack-years and incident tuberculosis.
* Among the 13,033 never-smokers exposed to secondhand smoke, 30 cases of incident tuberculosis occurred with an adjusted OR of 1.25 for active tuberculosis, but this association was not statistically significant.
* There was no dose-response association between passive exposure to smoking and the risk for tuberculosis.
* Overall, 17% of incident tuberculosis cases were attributable to smoking.
* When extrapolated to the national population, 2841 of 16,580 cases reported in Taiwan in 2005 were attributable to smoking.
* The authors concluded that current, but not ever, smoking was associated with an increased risk for incident tuberculosis and a greater intensity of smoking was associated with higher risk.


Clinical Implications

* Current, but not ever, smoking is associated with a higher risk for incident active tuberculosis, and this risk is greater in those younger than 65 years.
* There is a dose-response association for current smoking and incident tuberculosis but not for passive exposure to cigarette smoke and incident tuberculosis.

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