Household fuel use and pulmonary tuberculosis in central Nepal: A case-control study. Michael N. Bates, PhD School of Public Health University of California, Berkeley

Household solid fuel use For cooking and space-heating, about 3 billion people, mainly in developing countries and rural settings, use solid fuels: 2.4 billion--biomass (wood, charcoal, crop residues and animal dung) 0.6 billion—coal About 1.1 billion smokers worldwide 2

Traditional Biomass Stoves 3

TB risk factors include: HIV Immune suppression Diabetes mellitus Crowding Contact with TB case Alcoholism Silicosis Malnutrition Active tobacco smoking Household solid fuel use? 5

Biomass-TB study results Published biomass and TB disease study results, 2010 Biomass-TB study results

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Overall study objectives To determine whether the following are risk factors for (1) M. tuberculosis infection or (2) pulmonary TB disease: biomass fuel used for cooking or heating indoors kerosene used as a cooking or lighting fuel indoors

Study design Case-control study in Kaski and surrounding districts, central Nepal. Cases: 581 pulmonary TB disease Controls: 1,226 frequency matched by VDC or urban ward, population-based (both men and women). Anyone previously diagnosed with TB excluded from both case and control groups. Comprehensive investigation of household fuel use: cooking (LPG, wood, biogas) and secondary stoves heating lighting Extensive questionnaire to all participants. 9

Conditional logistic regression results for cooking (women only: 191 cases and 649 controls) Odds ratio* 95% Confidence interval Primary stove LPG 1.00 - Biogas 0.21 0.05, 1.00 Wood 0.17 0.07, 0.41 Secondary stoves LPG No Yes 1.55 0.44, 5.46 Biogas No 0.47 0.13, 1.71 Wood No 0.80 0.34, 1.90 *Adjusted for age, marital status, income, worked overseas, education, literacy, religion, caste, land ownership, kitchen location, home ownership, household crowding, smoking status, household owns means of transport, use of non-fuel lights, alcohol consumption, family member with TB in last 10 years.

Random-effects meta-analysis of all other TB-cookstove studies, ordered by publication year, 2017.

Meta-analysis of other studies of cookstoves and pulmonary TB Restricted to studies comparing biomass with gas (reference category) That is, excluded studies: Where different frequencies of biomass cooking were compared (N=2) When almost all participants used solid fuel (N=1) When either fuel category contained kerosene (N=2) Results for women used if available; if not, used combined results for men and women. Stratified according to whether prior TB cases excluded or not.

Random-effects meta-analysis of studies stratified by prior TB exclusion status Prior TB excluded Prior TB not excluded

Possible reasons for the difference between LPG and biogas Composition LPG is propane and butane Biogas is methane and CO2 Time of cook in kitchen when cooking

Women-time in kitchen during cooking, by primary stove type (data from a different ongoing study in Kaski district). Time in kitchen LPG stove N (%) Biogas stove Wood stove Total All or most. 112 (29.5) 3 (5.1) 32 (35.6) 147 (27.8) Some. 245 (64.5) 53 (89.8) 51 (56.7) 349 (66.0) Little or none. 22 (6.1) 6 (6.7) 32 (6.0) Outside kitchen. 1 (1) 1 (0.2) Total. 380 (100) 59 (100) 90 (100) 529 (100)

Women-time in kitchen during cooking, by primary stove type (data from a different ongoing study in Kaski district). Time in kitchen LPG stove N (%) Biogas stove Wood stove Total All or most. 112 (29.5) 3 (5.1) 32 (35.6) 147 (27.8) Some. 245 (64.5) 53 (89.8) 51 (56.7) 349 (66.0) Little or none. 22 (6.1) 6 (6.7) 32 (6.0) Outside kitchen. 1 (1) 1 (0.2) Total. 380 (100) 59 (100) 90 (100) 529 (100)

Main conclusions Cooking with LPG appears to be a risk factor for TB in people who have not previously had (pulmonary) TB. The mechanism is unclear, but might involve ultrafine particles. Lung damage from previous TB appears to increases pulmonary TB risk from biomass smoke. Cooking with biogas seems to be less of a TB risk factor in people without prior TB than cooking with LPG.

Funding National Institute of Environmental Health Sciences of the National Institutes of Health (grant number R01ES019624).

Thanks to the following: United States Ellen Eisen Laura Flores Phil Hopewell Nick Lam Ajay Pillarisetti Amod Pokhrel Karl Pope Lee Riley Kirk Smith Nepal Ambika Baniya Avash Bhandari Dirgha Ghimire Krishna Ghimire Birenda Kunwar Madhu Maya Pahari Ramesh Kumar Rijal Tula Ram Sijali Sharat Verma And many more…

Thank you! Thank you! 20