Drug-resistant TB on the increase

A record number of multidrug-resistant tuberculosis (MDR-TB) cases have been documented in the most extensive global survey of its kind. The findings were released this week by the World Health Organisation (WHO).

The report estimates that nearly half a million new cases of MDR-TB emerged in 2006, about 5 percent of all new TB cases. MDR-TB is a form of the disease that does not respond to standard treatment, either because of failure to complete first-line treatment or because of infection from one person to another. China, India and the Russian Federation are thought to carry the largest MDR-TB burden, with China and India accounting for 50 percent of the global caseload.

"TB drug resistance needs a frontal assault. If countries and the international community fail to address it aggressively now, we will lose this battle," said Dr Mario Raviglione, director of the WHO Stop TB Department.

"In addition to specifically confronting drug-resistant TB and saving lives, programmes worldwide must immediately improve their performance in diagnosing all TB cases rapidly and treating them until cured, which is the best way to prevent the development of drug resistance."

Data used to compile the report, Anti-tuberculosis drug resistance in the world, the fourth since 1997, was collected from 81 countries between 2002 and 2006 and represents over 35 percent of the global total of new TB cases recorded in that time.

TB drug resistance needs a frontal assault. If countries and the international community fail to address it aggressively now, we will lose this battle.

Although data from 33 countries not previously covered is included, the authors acknowledge that there are still significant gaps in coverage. Only six countries in Africa - the region with the highest incidence of TB in the world - were able to provide drug-resistance data. Other countries lack the laboratory or human resource capacity to detect drug-resistant TB.

It is estimated that as many as half of all adults in southern Africa carry a latent form of TB. People with HIV-compromised immune systems are 50 times more likely to develop active TB, but the sputum tests most commonly used to detect TB often fail to recognise it in HIV-infected patients.

In most HIV-positive patients with negative sputum test results, the most reliable way to diagnose TB is by culture testing, in which samples are cultivated in a special liquid. However, few countries in Africa have the equipment to perform culture testing.

Based on the available data, the WHO estimates there were 66,700 MDR-TB cases in Africa in 2006. However, the survey was based on smear-positive TB cases. The authors note that in countries with high HIV prevalence, both the proportion of drug resistance among patients co-infected with HIV, and the extent of links between HIV and drug-resistant TB could have been under-represented in the survey.

Only seven countries provided data on drug resistance that included the patients' HIV status. In Latvia and Ukraine, the only two countries where the number of co-infected cases was large enough to examine the connection between the two epidemics, TB/HIV patients were nearly twice as likely to have MDR-TB as HIV-negative patients.

For the first time, the survey also includes data on extensively drug-resistant (XDR) TB, a strain that is resistant to both first and second-line treatment. Forty-five countries reported at least one case of XDR-TB, but the true scale of the problem remains unclear because many countries still lack the equipment to test for resistance to second-line TB drugs.

Citing the deadly outbreak of XDR-TB in South Africa's KwaZulu-Natal Province in 2006, which mainly affected HIV-positive patients, the report warned: "Detection of this outbreak was only possible because of the extensive laboratory infrastructure available in the country.

"It is likely that similar outbreaks of drug resistance, with associated high mortality, are taking place in other countries but currently going undetected due to insufficient laboratory capacity."

Although South Africa was not among the countries that contributed data to the survey, recent figures show that nearly 6 percent of 17,615 MDR-TB cases detected over a four-year period were extremely-drug resistant; 14 percent of drug-resistant cases in KwaZulu-Natal Province were XDR.

South Africa is one of only two countries on the continent with the equipment to diagnose XDR-TB. According to Dr Paul Nunn, co-ordinator of the WHO's TB/HIV and TB Drug Resistance Unit, other countries in Africa have "a very long way to go" before they have similar laboratory capacity. "There are a number of countries in Africa that do not have a single laboratory capable of testing a culture for drug resistance," he told IRIN/PlusNews.

Nunn pointed out that Africa may have a relatively low incidence of MDR-TB because some of the first-line TB drugs available in Europe and other parts of the world were only introduced recently in Africa, meaning that resistance has had less time to develop.

The WHO is currently revising the MDR component of its Global Plan to Stop TB, to define how to achieve the goal of universal access to diagnosis and treatment for all MDR-TB patients by 2015. The plan also aims to halve TB prevalence and deaths compared with 1990 levels, and increase funding for research into new diagnostics as well as new drugs that would be effective against resistant strains, and a TB vaccine.

The WHO estimates a US$2.5 billion funding shortfall to finance TB control in 2008, including US$500 million needed to address MDR and XDR-TB.

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