The association between smoking and TB disease is supported by substantial body of epidemiological evidence gathered over the past 50 years, which shows that smoking is a risk factor for TB infection and for the development of pulmonary TB.
Smoking increases the risk of Mycobacterium tuberculosis infection, the risk of progression from infection to disease, and the risk of death among TB patients.
Nearly 61% of TB deaths are attributable to smoking. Among children living with a patient with active pulmonary TB, passive smoking accelerates the development of active TB.
The risk of prevalence of TB infection is more among current or ex-smokers than never smokers. The risk of TB is more with the duration of smoking than the number of cigarettes smoked daily.
The biological basis by which smoking increases the TB risk may be through a decreased immune response, mechanical disruption of cilia function, defects in macrophage immune responses, and/or CD4+ lymphopenia, thereby increasing the susceptibility to pulmonary TB.
Smoking reduces the defences on the surface of the respiratory apparatus, alters the mucociliary apparatus through cell destruction and dysfunction and reduces lysozyme A activity. As a result, germs and toxic substances reach the alveolar tissue in greater numbers. Smoking also produces alterations in both natural and acquired cell immunity, affecting macrophages and leukocytes. It induces apoptosis in both activated and non-activated macrophages, leading to the multiplication of the bacilli.
Smoking influences the clinical progress of TB lesions. Smokers tend to have more cavitary disease, and greater severity despite diagnostic delays similar to those among non-smokers.
Interventions against TB should include messages to increase public awareness on the dangers of smoking. Action against smoking and hazardous lifestyles and living conditions can help reduce the impact of TB in the community.
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