Impaired pulmonary function and the risk of tuberculosis: a population-based cohort study

To the Editors: It is well known that pulmonary tuberculosis (TB) can cause lung impairment leading to chronic obstructive pulmonary disease (COPD) 1, but less is known to what extent impaired lung function increases the risk of TB. A case–control study from the UK found patients with emphysema to have a three-fold increased risk of TB, adjusted for smoking and the use of corticosteroids 2. A cohort study from Denmark found moderate-to-severe COPD to be associated with a two- to three-fold increased risk of hospitalisation with TB 3. We have previously shown that patients hospitalised with COPD have a three-fold increased risk of active TB compared with population controls 4. In the present study, we examine the risk of active TB in relation to lung function in a cohort who underwent spirometry in 1974–1992. Between 1974 and 1992, 22,444 males and 10,902 females, born 1921–1949, participated in a health screening programme, the Malmo Preventive Project. Complete birth cohorts, born in pre-specified years, from the city of Malmo were invited; the overall participation proportion was ∼70% 5. The screening included physical examination, spirometry, blood samples and assessment of lifestyle factors by means of a self-administered questionnaire. Some questions varied between the cohorts. We excluded 4,413 individuals because of missing spirometry data; 26 individuals were excluded because of missing data on either body mass index (BMI), smoking or immigration status, leaving a total of 28,907 individuals in final analysis (21,174 males and 7,733 females). BMI as was calculated as mass/height2 (in kg·m−2). Individuals were regarded as having diabetes mellitus if they answered positively to the question “Do you have diabetes mellitus?” or their fasting blood glucose level was ≥6.1 mmol·L−1. Around 96% of the cohort (n = 27,789) answered questions on alcohol. Individuals …