Communicable diseases specialists will gather in Johannesburg this week for a conference on the topic amid fears that a sharp rise in treating tuberculosis will add to the burden on already overstretched public health budgets.

Karin Weyer, a tuberculosis expert at the Medical Research Council, said that an outbreak of extreme drug resistant (XDR) form of the disease in the eastern KwaZulu-Natal province of South Africa earlier this year had set alarm bells ringing about its devastating consequences.

Fifty-two of the 53 patients who contracted XDR-TB in the Tugela Ferry area of KwaZulu-Natal province, one of the provinces with the highest rates of HIV in the country, died from the outbreak, Weyer told AFP.

"They were all HIV positive. This is the frightening thing, XDR-TB has the potential to spread very rapidly in HIV-positive individuals and there is a very quick, very high mortality among patients. In this particular outbreak they died in a median of 16 days," Weyer said.

At any given moment, about 330,000 South Africans have tuberculosis and about 6,000 have the multiple drug resistant (MDR) variant.

South Africa has the highest number of HIV sufferers in the world after India, with 5.5 million of the country's 47 million-strong population affected by the disease.

Organisers of the two-day conference from Thursday -- which will be attended by representatives of the Medical Research Council, World Health Organisation and US Centres for Disease Control -- said the rise of XDR cases was emerging as a "major threat to successful HIV treatment and care in sub-Saharan Africa."

"Though data are limited, population-based surveillance has demonstrated increasing levels of MDR-TB in Botswana, Mozambique and South Africa," they said in a statement.

Nomfundo Eland of South Africa's main anti-AIDS lobby group, the Treatment Action Campaign, said many tuberculosis patients had contracted the disease as they had not followed their full course of drug treatment.

"When they fail to to so, they often develop MDR-TB," she said.

The source of the Tugela Ferry outbreak "was probably an MDR-TB patient who didn't complete his treatment and as a result then developed XDR TB and spread this to HIV-positive patients," the MRC's Weyer added.

MDR-TB was generally resistant to isoniazid and rifampicin, the two main antibiotics traditionally used to fight tuberculosis.

"XDR-TB means they are resistant also to other drugs, including those available to treat MDR-TB," Weyer added. "This makes it a very serious thing because we have no drugs to treat it with."

While the prevalence of MDR-TB was still relatively low at 2.9 percent of tuberculosis patients, it was increasing and costs significantly more to treat.

Normal strains of tuberculosis can be treated at a cost of 400 rand (60 dollars) per person but MDR variants can cost up to 100,000 rand.

"The threat to the broader community is fortunately much lower and I'm saying that because when someone is HIV- negative and that person gets infected with TB or MDR-TB or XDR-TB, there is only about a 10 percent lifetime risk of that infection turning into active disease, so it is a small risk," said Weyer.

"But when the immune system gets under pressure, like what happens with HIV-positive individuals, then that 10 percent lifetime risk is compounded to a 10 percent annual risk."

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