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Smear positivity of index cases may have confounded the effect of smoking

Posted by cicmed on 14 Nov 2012 at 08:50 GMT

This study shows that smoking was associated with LTBI after adjusting by known confounders including exposure to index cases with tuberculosis in the household. However, the authors did not adjust by smear status of index cases which may have confounded the effects of smoking specially when the association was not robust. In 2010 45% of pulmonary cases in the USA were smear negative and 43% were smear positive (1). Household contacts exposed to smear positive cases have higher rates of LTBI and disease compared to household contacts exposed to smear negative cases. If the smokers in this study were more exposed to AFB positive cases as compared to non-smokers then the effect of smoking on LTBI may have been confounded by smear positivity of their index cases i.e. assuming that all index cases had pulmonary TB as site of disease was not ascertain in the study.
1.-Reported tuberculosis in the United States 2010 (accessed November 14, 2012)

No competing interests declared.