Household fuel use and pulmonary tuberculosis in central Nepal: A case-control study.

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

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

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) *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).

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 • AmodPokhrel • Karl Pope • Lee Riley • Kirk Smith Nepal • AmbikaBaniya • Avash Bhandari • DirghaGhimire • Krishna Ghimire • BirendaKunwar • Madhu Maya Pahari • Ramesh Kumar Rijal • Tula Ram Sijali • SharatVerma And many more…

Thank you! Thank you! 20

Household fuel use and pulmonary tuberculosis in central Nepal: A case-control study.