1. 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

2. 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

3. Traditional Biomass Stoves3

5. 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

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

7. 7

8. 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

9. 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

10. 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.

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

12. 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.

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

14. 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

15. 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)

16. 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)

17. 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.

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

19. 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…

20. Thank you!
Thank you! 20