Leprosy Mailing List – March 4, 2013
Ref.: (LML) New Diagnostic Test
From: Wim van Brakel, Royal Tropical Institute, Amsterdam
Dear Dr. Schreuder,
With interest I have read the various contributions to the 'New Diagnostic Test' discussion. It was presented as 'the answer to the leprosy problem'. "This will bring leprosy management out of the Dark Ages", so it was claimed. Fortunately for the hundreds of thousands of new leprosy patients detected each year, leprosy management has come out of the Dark Ages a long time ago in most endemic countries, especially in Brazil where the test was launched. Most people are diagnosed well, given free MDT and every effort is made to prevent them developing permanent disabilities.
Would a test for leprosy not be useful? Yes, it would be! There are several situations in which a reliable test with high sensitivity and specificity would be very useful.
1. Diagnosis of suspect cases who lack clinical cardinal signs of leprosy.
Normally speaking, leprosy is diagnosed by clinical examination. For the majority of patients, this is perfectly adequate, since the signs and symptoms are clear and easy to recognize for the trained health worker. However, research has shown that, in about 30% of multibacillary (MB) cases, the tell-tale anesthetic skin lesions and clearly enlarged peripheral nerves are absent during the early stages of clinical disease. This makes this category difficult to diagnose. From a diagnostic perspective, this group, and other suspects who do not have the 'cardinal signs' of leprosy, could benefit from a laboratory test. In other patients, adding a lab test may make leprosy control much more complicated and unnecessarily expensive. One could debate at what level such a test should be available, but this is probably at the first referral level.
2. Predicting leprosy in contacts of leprosy patients IDRI – the makers of the test – expect the test "to detect infections as much as a year before symptoms appear." In other words, the test will predict leprosy in persons at risk. The only context in which this could be used is in contact screening, since mass population screening will never be cost-effective no matter how good the test. If we had a test that could reliably predict whether a given contact of a known leprosy patient is infected and will develop leprosy, then preventive treatment could be given. This would indeed be a big step forward, since such early treatment will most likely lead to a disability-free cure. In addition, the person would not need to be labeled as a 'leprosy patient', thus potentially preventing social problems due to stigma as well. However, as far as I have been able to find out, prospective evidence from cohort studies of the predictive value of the new test is still lacking.
At the moment, the Indonesian government and NLR are involved in an operational study of chemoprophylaxis using a single dose of rifampicin. The chemoprophylaxis is given to a group of 20 contacts of each new case, including household members, neighbours and social contacts. Research has shown this intervention to reduce the risk of leprosy by ~60% in the chemoprophylaxis group. In this context, a test for leprosy could be used in two ways. One could test all the contacts and only give chemoprophylaxis to those testing positive. This would probably reduce the number of people needing rifampicin significantly. However, it would be a question what treatment should be given. If the predictive value of the current test is confirmed, it would indicate that contacts may be developing MB leprosy. Is a single dose of rifampicin an adequate treatment for that? Nobody knows. This will require further intervention research, once the properties of a new test have been confirmed.
In addition, in the chemoprophylaxis context, one would need a test that would detect both MB and PB leprosy. Otherwise, people developing PB leprosy would be wrongly excluded from chemoprophylaxis. Having a test will not help to overcome the significant difficulties with disclosure, informed consent and stigma that are reported from the pilot area.
3. Providing evidence that leprosy is a real disease. One potential advantage of a test is of a non-biomedical nature. A diagnostic test for leprosy would help to bring the disease out of the mystical sphere that still surrounds the disease in many cultures. NLR-sponsored anthropological research has demonstrated this at the time when the PGL-1 lateral flow test was being field tested. Patients, household members, health workers and others interviewed in several countries were positive about the test, despite the fact that it failed as a diagnostic and predictive test on grounds of insufficient sensitivity, specificity and predictive value. Based on this experience, it is reasonable to expect that patients, their contacts and health workers will welcome a test for leprosy. It would help patients discuss the disease at home and may even help reduce stigma. If the latter would prove to be true, it would certainly be worth a dollar per patient.
In most leprosy-endemic settings, the most challenging tasks in leprosy control are training health workers, getting people to self-report when they have signs of leprosy, providing access to treatment, preventing permanent disability, reducing stigma and rehabilitation of those who already have developed disability. Despite a test for leprosy, these will continue to require dedicated staff and flexible, innovative leprosy control services that operate through the general public health system. A new test, even if excellent, will at best make a small contribution to this very complicated work.
Dr. Wim van Brakel
Technical Advisor NLR
Royal Tropical Institute, Amsterdam, Netherlands
LML - S Deepak, B Naafs, S Noto and P Schreuder
LML Archives: http://www.aifo.it/english/resources/online/lml-archives/index.htm
Contact: Dr Pieter Schreuder << editorlml@gmail.com >>.
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