Factsheets

Drug Resistant TB

When TB patients are not prescribed their drugs properly or do not take their medicines as prescribed, TB bacilli become resistant to a certain drugs. This means that that drug is no longer effective against the TB bacillus.

Multidrug-resistant TB, or MDR TB refers to Mycobacterium Tuberculosis isolates that  are resistant to at least both isoniazid and rifampicin, the two most powerful anti-TB drugs. This is a very serious problem. People with MDR TB disease can only be treated with reserve or second-line drugs. These drugs are not as effective as the first-line drugs. They also cause more side-effects.

 People who have spent time with someone sick with MDR TB disease can become infected with TB bacteria that are resistant to several drugs. Close contacts of patients therefore must be carefully examined for active disease and treated accordingly. This is particularly important for people who are at high risk of developing MDR TB disease, such as children and HIV-infected people. 

Drug resistance develops when people

     are not prescribed or do not take their medicines properly

     develop TB disease again, after having taken TB medicine in the past 

     have spent time with someone with drug-resistant TB disease 

MDR TB: Epidemiology in the Region

Emerging MDR-TB is posing a new threat to TB control in the Region. Three countries in the Region India, Nepal and Thailand, have been participating in successive rounds of DRS held since the late 1990s. While higher rates of drug resistance to any anti-TB drug have been reported, the mean prevalence of MDR-TB among new smear-positive cases in the South-East Asia Region is estimated to be low, at an overall 2.2%. MDR-TB rates reported from countries in the Region are as shown in the table below. Isolated reports of higher levels of MDR-TB are reported mainly from hospital settings. Levels as high as 60% are reported among previously treated cases in tertiary care facilities. 

Multi-drug resistance rates in SEAR

Next steps:

The establishment of nation-wide regular DRS in countries in the Region and particularly in all five high TB burden countries is thus a priority. Recently a DRS survey was completed in Myanmar and national DRS surveys are expected to commence in Bangladesh, Indonesia and Sri Lanka in 2006. India and Nepal have established projects according to international guidelines, in close consultation with the Green Light Committee that has been set up to assist countries in establishing treatment for cases with multidrug resistance under national programmes. 

Future strategies for MDR-TB

The Regional Strategic Plan for 2006-2015 includes establishing interventions to address MDR-TB:

     Assisting countries in building laboratory capacity to undetake quality assured culture and drug susceptibility testing

     Intensifying and expanding surveillance for MDR-TB in the Region.

     Strengthening capacity to diagnose and manage MDR-TB including ensuring essential standard of care.

     Assisting countries with preparing general health systems to deliver MDR-TB interventions.

XDR-TB – Extensive Drug-Resistant TB

XDR TB, or extensive drug-resistant TB, is currently defined as resistance to the 2 most potent anti-TB drugs, isoniazid and rifampicin, and resistance to at least 2 of the 6 classes of second-line drugs.  These strains leave patients without treatment options that meet international standards and are therefore virtually untreatable.

The emergence of XDR-TB Findings from a WHO/US CDC survey of 14 supranational TB reference laboratories, using a 17,690 convenience sample from 49 countries, were reported in March 2006.  XDR-TB was documented in 10% of the detected MDR-TB cases, and was present in 17 countries.  In USA, Republic of Korea and Latvia, population-based studies showed that 4%,15% and 19% respectively, of MDR-TB cases were XDR-TB. Following an outbreak of XDR-TB in KwaZulu Natal in South Africa and in recognition that XDR-TB is a threat to the major gains made in global TB control, WHO issued a global alert in September 2006, over the emerging threat of these highly lethal strains of drug-resistant TB.

Extent of XDR-TB in the SEA Region: Very little data is available from countries in South East Asia. Detection of XDR-TB requires drug susceptibility testing for resistance to second-line drugs, which is technically difficult and only done at a very small number of laboratories. Second-line drug susceptibility testing has been performed at the Tuberculosis Research Center, Chennai, for many years. Between May 2000 and March 2005, 66 patients from the Chennai area with MDR-TB had isolates tested for second-line drug resistance to 3 classes of second line drugs (flouroquinolones, aminoglycosides, and ethionamide). Resistance to all three tested classes of second line drugs (XDR) was found in 1 isolate (1.5%). While this represents a minimum estimate due to the limitations in testing, these findings suggest that XDR-TB is rare at this time.

Implications

The emergence of XDR TB could seriously jeopardize the success of TB control programs in the Region. Second-line drugs are widely available throughout the South East Asia region, the majority of which are prescribed outside of national programmes, in the absence of treatment protocols for MDR-TB patients under national TB programmes except at pilot sites. It is therefore unknown how many patients are being treated using these drugs.

Action to combat XDR-TB

An emergency meeting of experts was held in September 2006, co-organized by the South African Medical Council, CDC and WHO. WHO was requested to urgently establish and lead a global task force on XDR-TB. This task force has now been formed with following aims:

     Development of an appropriate coordinated global response to XDR-TB

     Ensuring timely and effective response to requests for assistance from countries

     Provision of a pro-active flow of information to all stakeholders, including Governments and the media

     Mobilization of sufficient funds to support efforts globally to combat MDR-TB and XDR-TB

Next steps to support countries in the Region:

     Intensifying support and resource mobilization for tuberculosis control programmes, with focus on MDR prevention through the DOTS strategy.

     Strengthening national capacity for quality-assured laboratory diagnosis of MDR and XDR-TB

     Promoting appropriate treatment of MDR-TB through expansion of DOTS-Plus treatment programmes

     Gathering the evidence needed to inform ongoing response and action for this emerging challenge

     Provision of a pro-active flow of information to all stakeholders, including Governments and the media

Latest information and regular updates on XDR-TB and related TB issues are published on the WHO Stop TB website at www.who.int/tb and on the Stop TB Partnership web site at www.stoptb.org