Household fuel use and latent tuberculosis infection in a Nepali population

The risk of developing latent tuberculosis infection (LTBI) associated with cooking with solid fuels is unknown. This study examined the relationship between household fuel uses and LTBI in adults living in Nepal, a country with a high incidence of tuberculosis.

Participants were 1088 adults aged 18-70 years, members of the control group of a population-based case-control study of pulmonary TB (PTB) in people without previous TB, living in Kaski and neighboring districts of Nepal. Participants were interviewed in their homes with a standardized questionnaire. Blood samples were tested for LTBI using an interferon-gamma release assay. Multivariate unconditional logistic regression was used to examine associations between household fuel sources and LTBI.

The overall prevalence of LTBI in the study population was 36%. Using liquefied petroleum gas (LPG) as the baseline cooking fuel type, the adjusted odds ratio (aOR) for using a primary wood cookstove was 1.13 (95%CI: 0.73,1.77) for all participants and, in women only, 1.14 (0.62, 2.09). Corresponding figures for biogas stoves were 0.64 (0.34,1.20) and 0.59 (0.24,1.45), respectively. Household sources of air pollution positively associated with LTBI included traditional oil lamps (diyos) used during power outages, for which the aOR in all participants was 2.53 (1.20, 5.31), although the number of users was small. Use of candles for lighting was also associated with increased risk of LTBI among men (aOR = 1.61, 95% CI:1.01, 2.56).

No association was found between use of wood for cooking and LTBI. However, there was some evidence that biogas cookstoves were associated with reduced odds of LTBI. Some exposures at the time of actual infection will have been different than the current exposures used in the analysis, biasing results towards the null. Results are sufficient for the use of diyos to be discouraged for lighting purposes. Overall, results suggest that household cooking fuel use is likely to have more effect on moving from the infected state to PTB than on becoming infected with the M. tuberculosis complex. Further research, including longitudinal studies with serial LTBI testing would be useful to more accurately assess the relationships between exposures and infection.