Drug susceptible TB is the opposite of drug resistant TB. If someone is infected with TB bacteria that are fully susceptible, it means that all of the TB drugs will be effective so long as they are taken properly. It still means that several drugs need to be taken together to provide effective TB treatment.
Drug susceptibility testing is how you find out which drugs will be effective against certain TB bacteria.
There are two ways that people get drug resistant TB.
In 2013 the World Health Organisation (WHO) estimated that 3.5% of new cases and 20.5% of previously treated cases of TB were of MDR (Multi Drug Resistant) TB. There were an estimated 300,000 new cases of MDR TB among those cases of pulmonary TB that were reported to them.2 MDR TB is just one of the different types of drug resistant TB, and is TB that is resistant to the TB drugs isoniazid and rifampicin.
It was also estimated that there were 480,000 new cases of MDR TB among the world’s 12 million prevalent cases of active TB. The number of prevalent cases of MDR-TB is important as it directly influences the active transmission of strains of MDR TB.3 (For more about TB incidence and prevalence see the TB statistics page.) There were also approximately 210,000 deaths from MDR-TB and more than half of these patients were in India, China and the Russian Federation.
The WHO is starting to look at trends focusing on the period 2008 – 2011. The current figures suggest that globally the estimated proportion of new cases with MDR-TB has not changed and remains at about 3.5%.
Some organisations believe that the current statistics for drug resistant TB greatly underestimate the extent of the problem.
“Wherever we’re looking for drug resistant TB we’re finding it in very alarming numbers. And that suggests to us that the current statistics that are being published about the prevalence of multi drug resistant TB are really just scratching the surface of the problem.”
Dr Leslie Shanks, Medical Director, MSF4
There are 27 “high burden” countries. These are countries where there are at least 4,000 cases of MDR TB each year and/or at least 10% of newly registered TB cases are of MDR TB.8
The 27 “high burden” countries are:
Armenia, Azerbaijan, Bangladesh, Belarus, Bulgaria, China, Democratic Republic of the Congo, Estonia, Ethiopia, Georgia, India, Indonesia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Myanmar, Nigeria, Pakistan, Philippines, Republic of Moldova, Russian Federation, South Africa, Tajikistan, Ukraine, Uzbekistan, Viet Nam.
The cost of just the drugs for treating the average multi drug resistant TB patient can be 50 to 200 times higher than the cost of treating a drug susceptible TB patient. The total costs though are much more than just the drug costs, and must include such costs as the equipment for diagnosis as well as all the labor costs.
In addition although the disease may be the same in different countries of the world, the overall costs of treatment can be very different. This is not just because the finances and facilities may be different, but also because the expectations of both patients and health care workers and what is considered to constitute good treatment may be different.
For example, in many countries discussion about the costs of drug resistant TB may well be about using DOTS Plus and whether it can be afforded, and can the system possibly afford drug susceptibility testing on all initial isolates of TB, as well as the cost of second line drugs for the treatment of drug resistant TB.
By contrast, in many parts of the United States and in some parts of Western Europe, the political and social pressures regarding the financing of drug resistant TB control may well be to locate enough money for negative pressure isolation rooms, so that every single patient coming through the door of a hospital who might possibly have pulmonary TB, can be put in such a room and kept there until it has been proven that they have not got drug resistant TB.8
However, short term decisions about, for example, the affordability of drug susceptibility testing, can and indeed does result in a lack of effective treatment for drug resistant TB in many countries and areas. This not only causes many unnecessary deaths, but also helps to fuel the ongoing spread of drug resistant TB.
There are a number of major problems with providing effective treatment for drug resistant TB. Although many of these also apply to the provision of treatment for drug susceptible TB, they are particularly important in respect of the large scale effective provision of treatment for drug resistant TB.9 10
Globally there is very limited capacity to rapidly diagnose drug resistant TB. Although some new TB tests are becoming available such as the Xpert TB test, point of care testing is still practically non existent in the areas with the highest TB burden. To overcome the problems of drug resistant TB there needs to be development of true point of care drug susceptibility tests, and their widespread implementation at affordable cost.
National TB control programs must include a universal right to treatment for drug resistant TB. It is now accepted that there is a universal right to treatment, for the treatment of HIV/AIDS. Treatment for drug resistant TB should be viewed in the same way.
There also needs to be a significant increase in the number of manufacturers of quality assured second line anti TB drugs. Action needs to be taken on this by the Global Drug Fund (GDF) and the Green Light Committee (GLC), as well as by WHO and their international partners, as part of global TB control initiatives.
A major cause of the current drug resistance problems is the complexity and length of even the “basic” treatment regime for drug sensitive TB. There is an urgent need for new drugs with shorter simpler regimes for drug sensitive TB, as well as new drugs for the treatment of TB that is resistant to all the current TB drugs.
“These drugs are so horrible to eat every day. After nearly a year and a half, I thought it was just too much; I couldn’t keep taking all those pills. I thought it would be OK if I stopped taking them. But they told me if I didn’t keep going I might get sick again and then I would have to start again from the beginning with all the injections. So I kept going with the pills and now I am cured. It was such a long time.”
Drug resistant TB patient11
In areas of minimal or no multi drug resistant TB, TB cure rates of up to 95 per cent can be achieved. Cure rates for multi drug resistant TB are lower, typically ranging from around 50% to 70%.12
At the level of global TB control there is a tension between concentrating on either drug susceptible or drug resistant TB. Some people consider that the way forward is to concentrate on drug susceptible TB, and to particularly strengthen national TB control programs, believing that this will limit or even eliminate drug resistant TB. Others consider that drug resistant TB is where the emphasis must be.
“There is a need to directly confront MDR TB and XDR TB, whereas emphasis in the past has been on strengthening TB control programs per se, believing that we could thereby control the problem of MDR and XDR TB.” 13
At local, national and global level, the resources and the commitment need to be found to do both. National TB control programs need to more effectively find and treat people with drug susceptible TB, and they then won’t develop and spread drug resistant TB. There is also a need to find and treat those with drug resistant TB, to not only save their lives, but also to prevent them transmitting drug resistant TB to others. There is no reason why this should not be possible.
“Today MDR TB spreads unchecked in most of the world. It is fuelled by poverty at the individual and family levels, – limiting access to effective treatment – and at the regional and national level, where under resourced governments lack the capacity to tackle this disease.” 14
Drug-resistant TB 2014 Supplement Global Tuberculosis Report, WHO, Geneva, 2014 www.who.int/tb/publications/global_report/