The use of kerosene lamps may substantially increase the risk of tuberculosis (TB), according to a new study.
In Nepal, UC Berkeley researchers found the odds of having TB were more than nine times greater for women using kerosene lamps for indoor lighting, rather than electricity, and 3.5 times greater for women using biomass fuel for household heating, compared to those using cleaning-burning fuel stoves.
The study, published in the April issue of Environmental Health Perspectives, provides the first evidence that exposure to kerosene stoves or lamps and biomass fuel for heating may play a role in increasing TB risk.1
TB is a major health issue in the developing world. In 2008, there were over 9 million new cases and 1.3 million TB-related deaths.2 People spread the bacteria through the air when they talk, cough, spit or sneeze. Not everyone infected will develop the disease, although people with compromised immune systems are more vulnerable. Globally, TB infection spreads once every second.3
In Nepal, almost half the population of 28 million lives below the international poverty line of $1.25 US per day. Forty-five percent are infected with the TB organism, Mycobacterium tuberculosis, and 11,000 die annually of TB, according to lead author Amod Pokhrel, a doctoral candidate at UC Berkeley.
Cooking and heating with biomass fuel is common in developing countries, including Nepal and its border countries of China and India, but potentially the practice comes at a high price to public health.
Smoke from poorly ventilated biomass stoves is known to be hazardous, especially for women who do most of the cooking. It's associated with acute lower respiratory infection in children, chronic obstructive pulmonary disease (COPD) and ischemic heart disease.4 Adding to the problem, incomplete combustion of biomass fuel produces greenhouse gas pollutants and global warming.5
In the new study, researchers enrolled 125 women with TB from the Regional Tuberculosis Center and the Manipal Teaching Hospital (MTH) in Pokhara. TB diagnosis was confirmed by chest X-ray and sputum testing. Two-hundred and fifty female outpatients from MTH of similar age and without TB were recruited for the control group.
Six previous studies have examined the link between biomass fuel and TB, with inconsistent results.6 To address the limitations of these earlier studies, Pokhrel and his colleagues developed a comprehensive questionnaire to account for family income, smoking, alcohol consumption, household stove type, fuel used, kitchen ventilation and indoor lighting. Trained interviewers visited 28 participants at their homes to check the validity of questionnaire responses.
Study authors hypothesized they might find a connection between biomass fuels and TB. But when they examined the role kerosene cooking and lighting played in TB disease, “the results were alarming,” Pokhrel said.
“Right now 2 billion people are infected with the TB organism worldwide, but less than 1% have the disease at any one time. The question is, what are the risk factors that influence its development in those who are already infected?”
The findings were unexpected but make sense, according to co-author Michael Bates, professor of epidemiology at UC Berkeley. “Kerosene is widely regarded as a preferred alternative to biomass fuel, mainly wood and cow dung, which creates a lot of smoke and burns your eyes. But kerosene, which may appear to be cleaner burning, is actually a dirty fuel that gives off a lot of fine particulate matter.” And people are in close and prolonged contact with the lamps, often in poorly ventilated homes, increasing their exposure.
“Kerosene lamps are linked to socioeconomic status,” noted Pokhrel, who visited Nepal each summer from 2005-08. “They identify whether or not residents have electricity.” He said the government subsidizes kerosene because it is considered a clean fuel, but few studies have examined its impact on health.
“Right now 2 billion people are infected with the TB organism worldwide, but less than 1% have the disease at any one time. The question is, what are the risk factors that influence its development in those who are already infected?” asked Bates. “This study adds to the evidence for the need to reduce biomass fuel use, which is associated with other health outcomes like lower respiratory infections, COPD and possibly cataracts.” Bates said the relationship between kerosene and TB needs to be confirmed through other rigorous studies.
Along with Bates, Pokhrel co-authored the study with Kirk Smith, professor of global environmental health at UC Berkeley and several colleagues in Nepal. He received funding for his research from the NEWAID Foundation, which helps public health students study infectious diseases in the developing world. He was also supported by a NIEHS Fogarty scholarship through the International Training Program in Environmental and Occupational Health at UC Berkeley.
1, 6 Pokhrel AK, Bates MN, Verma SC, Joshi HS, Sreeramareddy CT, Smith KR. Tuberculosis and Indoor Biomass and Kerosene Use in Nepal: A Case-Control Study. Environ Health Perspect. 2010 Apr;118(4):558-64.
2, 3 World Health Organization
4, 5 Wilkinson P, Smith KR, Davies M, Adair H, Armstrong BG, Barrett M, Bruce N, Haines A, Hamilton I, Oreszcyn T, Ridley I, Tonne C, Chalabi Z. Public health benefits of strategies to reduce greenhouse-gas emissions: household energy. The Lancet. 2009 Dec;374(9705):1917-29.
Find this article and others online at http://coeh.berkeley.edu/bridges