The dawn of a New Era for TB diagnostics? HIV Update No. 8
December 2010
Summary
A new diagnostic tool has been developed, which represents an important breakthrough in the search for an efficient and accurate TB diagnostic tool. The new method (marketed as GeneXpert速 by Cepheid), is able to detect active TB and rifampicin resistance within 90 minutes. In-order to ensure that communities in high burdened and developing counties can benefit from it, the technology should be made widely available to countries at reduced cost. This method is still not suitable for point-of-care use; more research is required to produce a point-of-care diagnostic method for TB.
Background Tuberculosis (TB) continues to cause high disease burden in developing countries. In the year 2009 alone, 1.7 million people died from TB, equal to 4700 deaths a day. Of these, 380,000 deaths occurred in women. In the same year, there were 9.4 million new TB cases, of which 3.3 million were women and 1.1 million were among people living with HIV. In addition, the burden of multi-drug resistant TB has continued to rise. Multi-drug resistant TB is a form of TB that is difficult and expensive to treat and fails to respond to the most commonly used firstline drugs. It is estimated that in 2009, 3.3% of all new TB cases had multi-drug resistant TB. Extensively drug-resistant TB occurs when resistance to second-line drugs develops on top of multidrug resistant TB. Cases of extensively drug-resistant TB have been confirmed in more than 58 countries to date. Both multi-drug and extensive drug resistant TB pose an enormous challenge because they are difficult to treat, use expensive drugs which are not easily available, and whose use has to be sanctioned by the WHO. One of the key challenges of tackling the burden of TB disease has been the poor development of new strategies for detection and treatment of TB. Current diagnosis of TB relies on smear microscopy, which can produce results within 24 hours, and culture, which may require up to 6 weeks to produce results. 2
Limitations of current diagnostic methods: These methods (smear microscopy and culture) have been in use for more than a century and little innovation has been witnessed
since
culture
was
first
described. Pharmaceutical and research organizations
have
invested
far
less
resources into tuberculosis, (and other neglected tropical diseases) which affects many people in the low and middleincome countries, as compared to their investments into diseases associated with affluence such as cardiovascular and diabetes, thereby abrogating their moral duties to make new and effective technology and medicines available to the most poor. In addition these tools (smear microscopy and culture) often perform sub-optimally and may require laboratory infrastructure (and electricity) that may be unavailable in some settings especially in rural areas. In addition, although direct microscopy for AFB can lead to a diagnosis within 24 hours, this method is limited by its poor ability to correctly identify infected persons while correctly excluding persons who are not infected, especially in settings where TB is common.
How are smear microscopy performed? A diagnosis of TB can be made by examining a sample form a patient under a microscope. Such a sample is first smeared on a glass slide and is then treated with a special stain which enables detection of the mycobacteria that cause TB when examined under a microscope. If bacteria are identified in the sample, the test is said to be positive and this indicates TB infection. Where available, results should be confirmed by culture. How are cultures performed? Cultures are performed on respiratory samples such as sputum. Normal respiratory bacteria are first removed from such samples in order to reduce the chances of misdiagnosis. The sample as are then concentrated to increase the likelihood of detecting TB mycobacteria. The samples are then incubated with nutrient so that the TB mycobacteria can multiply. Culture results are more reliable. However, since mycobacteria multiply very slowly, the process of culturing can take two to six weeks.
3
In reality, and in most settings in the developing countries, smear microscopy is the only method of diagnosis of TB, since TB Diagnostic tools: Summary
culture is not widely available. However, health care workers may consider x-rays in combination with TB specific symptoms as realistic indicators that somebody is infected
Current tools
with TB.
Smear microscopy Culture X-ray
But even then, and in some settings, TB treatment cannot be initiated until confirmatory results (either a smear test or a culture) are available, resulting in long delays in diagnosis which can impede access to treatment and may also lead to
Newly WHO approved tools (2005 - 2009) Liquid culture Molecular Line Probe Assay (LPA) Strip speciation
increased transmission of TB because people do not know about their TB infection and therefore do not take the necessary steps to avoid infecting others. Consequently, and partly due to these diagnostic limitations, TB control has not been achieved at the global level, as evidenced by the growing TB burden as well as increased
Newly approved tool (2010) with potential for scale up
cases of multidrug-resistant and extensively drug-resistant
Automated detection and MDR screening (GeneXpert®)
ensure earlier diagnosis of TB which leads to earlier initiation
tuberculosis. Rapid and reliable tests are required in-order to
of treatment, reduces the likelihood of onward transmission and increases the effectiveness of TB control programs. Tools in late development Colorimetric redox indicator
New Development:
Front loaded smear microscopy
However a new method of diagnosis of TB, known as
Interferon gamma release assay (QuantiFERON®–TB)
GeneXpert® (Cepheid MTB/RIF Assay) appears promising.
LED fluorescence microscopy
diagnoses tuberculosis and detects resistance to one of the
It’s a closed, self-contained, and automated method which
most commonly used TB drugs (rifampicin) at the same time. Tools in early development
This new method of diagnosis has a number of key
Breathalyser screening test (has the best potential for community point of care)
advantages:
LAM detection in urine
system. Often times, samples may get contaminated during
Firstly there is less risk of contamination since it is a closed
the process of culturing leading to erroneous results.
4
Secondly, the risk of infection to the health worker is reduced since it is a closed system and requires a relatively short sample-handling period, compared to the several weeks it takes to grow a pure culture of TB mycobacterium. Health workers may get infected from handing sputum laden with TB mycobacterium. This risk is reduced in this diagnostic method because the potential exposure of the health care worker is reduced significantly. Thirdly, GeneXpertŽ produces the results within 90 minutes. This is in contrast to the several weeks it takes to make a diagnosis of TB using culture and the 1-2 days it may take to make a diagnosis on smear microscopy. Fourthly, the diagnostic platform not only makes a diagnosis of TB in 90 minutes possible, but it also determines the resistance to rifampicin, a key drug of Tuberculosis treatment. This is an important step towards diagnosing multidrug resistant TB. Rifampicin is one of the key drugs in the treatment of TB. There is a growing trend of rifampicin-resistant tuberculosis which is difficult to treat, often requiring expensive alternative drugs for a longer period of time. Technology The system relies on molecular analysis and combines on-board sample preparation with real-time PCR (polymerase chain reaction) amplification and detection functions for an integrated and automated nucleic acid analysis. The system is designed to purify, concentrate, detect and identify targeted nucleic acid sequences thereby delivering answers directly from unprocessed samples. Samples do not need to be pre-processed before using this system. Process The patient’s sputum sample is gathered in a bottle, a buffer fluid is added, and the sample is transferred to a cartridge which is then placed in the machine. The operator pushes a button and a result is obtained 90 minutes later. Broad Utility The diagnostic platform has a number of configurations and hence can be used for diagnosis of viral infections (such as Influenza) as well as other bacterial infections (such as Staphylococcus and Clostridium). It can also be used to monitor cancer patients.
5
Towards the Implementation of GeneXpert®: What are the Issues? Cost Firstly, the price of the system is too high. Current indications show that the machine will be available commercially at price estimated from 20,000 to 30,000 USD. This initial cost is prohibitively expensive for a rapid roll out to countries with the highest burden of disease and which are in most in need of such technology. The recurring cost of running the test is USD 30 for each test, mainly the cost of a cartridge, which is used every time a test is run. This cost per test is extremely high, considering the present global incidence of TB. Developing countries bear the burden of TB. Indeed, all the 22 high burden countries globally are low or middle income countries.
Price reduction for both the machine and the recurrent cartridge cost is necessary in order to make the machine (and technology) affordable in the regions where the epidemic is most serious, including sub-Saharan Africa which has some of the highest rates of multi drug resistant TB. In addition, the cost will be a major barrier to the availability to communities that require this technology. In-order to have comprehensive access to the new technology, the tests cost and acceptability to the new diagnostic method need to be carefully considered as key relevant factors.
Fitting the GeneXpert® diagnostic platform into the current health systems The new diagnostic method will have to fit into one of the level of the health systems, whether primary, secondary or tertiary. It is important for countries to determine where the diagnostic ability of the GeneXpert® will most useful and coherently fit, in line with the infrastructure and health personnel to sustain it. The level of fit will be different depending on the local context. However, in the long run, the technology should be available at the lowest level of health systems in countries where TB is a public health issue. Availability at Community Level The technology requires electricity and therefore this may be an immediate impediment for use of the machine in remote and rural areas where there is no electricity. Secondly, this system is still complicated for a lay person to operate and therefore may not match the skills set of a community health worker. It is still way off from the desired point of care diagnostic method – such as the rapid screening methods used for HIV testing. Community health workers, who perform intensified case finding, contract tracing and community based screening of TB suspects need to be equipped with a point-of-care tool which they can use at the community level with minimum technical skills.
6
Health Systems Strengthening The World Health Organization estimates that the current number of Tuberculosis cases reported by countries is far lower than the estimated true incidence of TB. Thus significant cases of Tuberculosis remain undiagnosed which continue to be an important source of new infections. The new GeneXpert® Diagnostic method has the potential to achieve the much desired increase in case detection of Tuberculosis disease as well as increased detection of Multidrug-resistant Tuberculosis. However, this means that health systems in developing and high-burden countries will have increased cases of Tuberculosis to treat immediately following widespread implementation of the new technology. Further, it is estimated that this new method of diagnosis, if widely scaled up, will also lead to early detection of tuberculosis since it can detect TB at lower concentrations as opposed to culture which depends on the presence of a significant amount of mycobacterium (at least 10,000 CFU/ML) for the disease to be detected. Consequently, widespread use of this method could lead to increased numbers of patients in need of TB drugs. As a result, more TB drugs, health personnel and infrastructure will eventually be required to keep up with the increased diagnostic capacity of the GeneXpert® and similar new technologies. This calls for the urgent need to ensure that the health system will be in a position to handle this increased demand for TB treatment and care. Impact Assessment New diagnostic methods such as the GeneXpert® are often scientifically-rated according to their specificity and sensitivity – i.e. ability of the test to correctly identify cases and correctly exclude the uninfected persons. However, in real terms, the ability of the test to increase the access to health care is of greater importance. Concrete evidence of the ability of this new technology to increase access to TB diagnosis, care and treatment needs to be examined and documented outside clinical trial settings. This operational research is urgently required in-order to inform the best approaches to scale up the implementation of the GeneXpert® (or similar) systems in different settings. It is important for countries to be engaged in the creation of protocols for use of new technologies, and for clinicians to be involved in demand creation. Community involvement is critical to ensure that the diagnostic gaps are highlighted and acted upon. In addition there is an opportunity to ensure that clear information on cost effectiveness is generated from settings outside clinical trials by early roll out of new technologies in high burden countries.
7
Children It is noted that the new diagnostic method still relies on use of sputum sample for diagnosis of TB. This method does not surmount the challenge faced in making a TB diagnosis among people who are unable to produce sputum, such as gravely sick persons or children. There is therefore a need to identify new biomarkers which could be used on the new diagnostic platform for enhanced diagnosis using other samples (e.g. blood, urine or stool). Conclusion This new diagnostic platform has moved closer to the objectives of simplifying and improving the detection of TB cases, including smear-negative sputum and drug- resistant cases. However, there is still a need to innovate and widely distribute a simple and cheap test that can be performed at the point-of-care level by both health care and community health workers. There is still no reliable method of identification of all latently TB infected cases. The search for reliable biomarkers for the various stages of TB infection needs to progress at a faster rate than presently is the case. Impact assessments of the new diagnostic method be performed urgently in-order to inform implementation in high burden and other countries.
8
References and further reading 1. WHO 2010 Global tuberculosis control. Geneva WHO 2. WHO 2010 Multidrug and extensively drug-resistant TB (M/XDR-TB): 2010 global report on surveillance and response. Geneva. WHO 3. Moore DF, Guzman JA, Mikhail LT. Reduction in turnaround time for laboratory diagnosis of pulmonary tuberculosis by routine use of a nucleic acid amplification test. Diagn Microbiol Infect Dis 2005;52:247--54. 4. Taegtmeyer M, Beeching NJ, Scott J, et al. Clinical impact of nucleic acid amplification tests on the diagnosis and management of tuberculosis in a British hospital. Thorax 2008;63:317-21. 5. CDC. National plan for reliable tuberculosis laboratory services using a systems approach: recommendations from CDC and the Association of Public Health Laboratories Task Force on Tuberculosis Laboratory Services. MMWR 2005;54 (RR-6):1-12. 6. American Thoracic Society; CDC; Council of the Infectious Disease Society of America. Diagnostic standards and classification of tuberculosis in adults and children. Am J Respir Crit Care Med 2000;161:1376-95. 7. Guerra RL, Hooper NM, Baker JF, et al. Use of the Amplified Mycobacterium tuberculosis Direct Test in a public health laboratory: test performance and impact on clinical care. Chest 2007;132:946-51.
Glossary (Alphabetical list) Assay: Laboratory test CFU: Colony Forming Units: a quantitative indicator of the presence of infectious agent in a sample. Extensively drug-resistant TB (XDR-TB) occurs when resistance to second-line drugs develops on top of MDR-TB Mycobacterium tuberculosis: Bacteria responsible for causing Tuberculosis infection and disease Multidrug-resistant TB (MDR-TB): Tuberculosis disease which does not respond to either Rifampicin or Isoniazid Rifampicin: one of the key dugs for the treatment of Tuberculosis Sputum: Viscous material that is derived from the lower air passages such as the lungs and bronchi that may contain substances such as mucus, blood, pus and/or bacteria; it is not the saliva that is produced by the glands in the mouth.
9
For further information please contact: Gitau Mburu, Senior Advisor: HIV and Health Systems E-mail address:gmburu@aidsalliance.org Telephone: +44(0)1273 718929 International HIV/AIDS Alliance (International secretariat) Telephone: +44(0)1273 718900 Fax: +44(0)1273 718901 mail@aidsalliance.org www.aidsalliance.org Registered British charity number: 1038860
10