Experts are sounding an alarm about a strain of tuberculosis that is effectively drug resistant.

Dr. Peter Small, senior program officer for TB with the Bill and Melinda Gates Foundation, says an increasing percentage of tuberculosis bugs are resistant to current drugs.

The World Health Organization estimates there are 8.8 million new TB infections globally each year. Of those, 27,000 people develop the drug-resistant TB that has been dubbed XDR-TB: Extensively drug resistant tuberculosis. About 16,000 people die of the strain.

XDR-TB is considered worse than multiple drug resistant TB, known as MDR-TB, which does not respond to a "first line" of drugs. The extreme strain responds to neither a "first line" of drugs nor a "second line" of drugs.

"This is a huge issue which is not being addressed and is not generally appreciated," Small told experts at the general meeting of the American Society for Microbiology this week, a major gathering of microbiologists and infectious diseases experts from across North America.

Canada is among 37 countries that have reported cases of XDR-TB. It's believed the bulk of infections to date have occurred in parts of Asia and the Russian Federation as well as some countries of southern Africa.

In Africa, TB treatment is complicated by high rates of HIV infection, which lowers a person's immune system. In parts of sub-Saharan Africa, it is believed as few as one in 10 XDR-TB patients survives.

"MDR-TB and XDR-TB and the way they are magnified by HIV infection is the biggest public health challenge both nationally and internationally," Dr. Fabio Scano, a TB expert from the World Health Organization, said recently.

Drug resistance grows when patients do not complete the required six-month regime of medication.

In South Africa, the health department has had to force a number of XDR-TB patients back to hospital after they tried to return to their homes. And in the United States, a 27-year-old man suffering from the extreme strain has been locked up indefinitely as a danger to the public.