Researchers also found that indoor air pollution from such sources as passive smoking and burning wood and charcoal may be associated with increased risk of infection, disease and death from tuberculosis. TB, a highly contagious disease, is caused by airborne bacteria and typically affects the lungs. People with TB have frequent coughing spells, often coughing up discolored mucus from their lungs. They may lose weight from lack of appetite and have fatigue, chills and mild fevers.

According to the U.S. Centers for Disease Control and Prevention (CDC), 10 million to 15 million people in the United States have latent TB, meaning they are infected with the bacteria but have no symptoms and are not contagious. People with active TB have symptoms and can infect others. The CDC estimates there were over 14,000 active TB cases reported in the country in 2005. Up until the mid-1900s, TB was a serious health threat worldwide. The advent of antibiotics lessened the threat in most developed nations. However, TB is still a serious health risk in developing parts of the world. World Health Organization data show 8 million people develop active TB and almost 2 million people die from it globally every year.

TB risk is most often associated with people who have HIV/AIDS, weakened immune systems and use illegal drugs and alcohol. Older people, those born in areas where the disease is more prevalent (i.e., Africa, Asia, Latin America) and people living in close or crowded conditions such as prisons and nursing homes are more susceptible to TB infection. Smoking traditionally has not been considered a common risk factor for contracting the disease.

The Harvard researchers examined 38 studies that looked at the association between smoking, passive smoking and indoor air pollution and TB. They found that compared to nonsmokers, smokers were at an increased risk of testing positive for TB in tuberculosis skin tests, of having active TB and of eventually dying from the disease. They also noted that children who are not normally at high risk of disease but who were exposed to secondhand or passive smoking may be at greater TB risk.

Scientists are not certain how nicotine and other environmental pollutants work to cause TB. However, theories suggest that smoking and tobacco may impair the ability of cells in the lungs to fight off TB bacterium.

Researchers concluded that agencies working to control the worldwide spread of TB should look for more ways to reduce these potential causes. "TB control programs may benefit from including interventions aimed at reducing tobacco and indoor air pollution exposure, especially among those at high risk for exposure to infection," Harvard researcher Majid Ezzati said in a press release.

The study was published in the January 16 issue of the journal PLoS Medicine.

Copyright 2007 iVillage Total Health.