Smoking may be responsible for up to a fifth of tuberculosis (TB) infections and deaths world-wide, according to research presented at a global lung health conference in Cape Town on Friday.
"Probably more than 20 percent of the global TB burden may be attributable to smoking," researcher Karen Slama told journalists on the sidelines of the gathering arranged by the International Union Against Tuberculosis and Lung Disease.
"Smoking may increase the risk by about 20 percent of either getting infected, getting the disease, or dying."
Slama, head of operational research at the union's tobacco control department, said three separate reviews this year of research into tobacco use and TB infection, yielded "sufficient evidence" of a link.
"The evidence is mounting and coherent. Even a small effect would create a large and cumulative increase in infection, disease and death. This is very important information and now we have it," she said.
The research also found a significant link between passive smoking and TB infection.
"Among people infected with TB, effective tobacco control can lower the number of people that go from (latent) infection to disease ... to death," said Slama.
"Tobacco control can also reduce the pool of people that have TB. You can save millions of dollars in TB treatment costs."
Panelists told a press conference that smoking caused five million deaths a year, 13,400 a day and 560 an hour. This was expected to rise to 10 million by 2030 -- 70 percent of them in the third world.
There were an estimated 1.3 billion smokers in the world, growing to 1.64 billion by 2030.
Patricia Lambert, head of the Campaign for Tobacco-free Kids, said World Bank calculations showed the health and environmental costs of tobacco use to be 11 times higher than the industry's economic contribution.
Tobacco use fuelled poverty by diverting household incomes to cigarettes and healthcare costs, while absorbing an estimated six to 15 percent of governments' total health care costs.
The World Lung Foundation's Judith Mackay said smoking had been on the decline among men in developing countries, and had not significantly picked up among women, as had been expected.
But there appeared to be an increase among young people.
"Despite everything we do, we will see an increase in the number of smokers."
According to Sinead Jones, director of the union's tobacco control unit, tobacco use was one of only three causes of death on the increase globally. The others were obesity and HIV.
"We will have one billion (tobacco-related) deaths in the 21st century at the current trend," she said.
But resources for tobacco control have been lacking, with only three dollars spent on prevention for every death world-wide.
Lambert argued that no regulatory authority would ever license cigarettes for use if they were invented today.
"A cigarette is the only legally available consumer product that kills through normal use."