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New investigation tools for diagnosis of Pulmonary Tuberculosis

By JEEWAN PANDEY | 31 Mar, 2017

In poor countries like Nepal we still depend upon Mantoux test besides clinical examinations, chest xray and sputum examination for diagnosis of Pulmonary Tuberculosis. In case of Sputum negative samples, we then send Sputum forGeneXpert to diagnose the case. What other investigational tools can precisely help in diagnosis of PTB? What are the latest diagnostic investigations available? Are they feasible and readily available in country like ours?

Replies

 

mayuranki almaula Replied at 11:43 AM, 31 Mar 2017

Dr Pandey
A US based company called Codiagnostics has come up with a real time PCR test that is doing very well on pulmonary and extra pulmonary samples. We have just completed a detailed study in India and compared the outcomes even with other existing RT PCR systems that are closed system
It will be possible for us to help you out with a CoDx box which includes a small portable machine that is based on magnetic induction. We also have a melt technology on this system that helps with our drug resistant panel for TB
We have a group based in India. Please let us know how to reach you
Mayuranki Almaula

Dr. Saleh Mohammad Saleh Replied at 12:11 PM, 31 Mar 2017

One of those poor countries is Afghanistan that only tests such as Mantoux test, clinical examinations, chest x-ray and sputum examination for diagnosis of Pulmonary Tuberculosis.

Edward Nardell, MD Moderator Replied at 12:35 PM, 31 Mar 2017

Drs. Pandey and Almaula,

While the development of new diagnostics are encouraged, and need to be
tested in carefully controlled field trials, results published, and
approval from regulatory organizations like US FDA sought, companies should
not offer tests that have not been validated and approved for clinical use
outside of clinical trails. Dr. Pandey, I believe, is asking for additional
studies that are approved and affordable. Mayuranki appears to be offering
a test under development which should not be used for clinical decision
making until it is approved by local or international regulatory bodies. I
would not suggest using such tests for diagnosis until they are approved.
If it is an approved test, that is another story.

Re. diagnosing clinical tuberculosis, Dr. Pandey, except in children, the
TST is generally not recommended. In Nepal high rates of TST positivity are
found, so a positive test indicates Mtb infection or BCG vaccination, but
does not indicate active TB. Likewise, a negative test regularly occurs in
patients with clinical TB, so the TST is not a good rule out test. In
children, as part of a clinical diagnosis where bacteriological
confirmation is difficult, a positive TST is one factor favoring TB - in
part because positive reactions in young children is less common despite
BCG.

Ed Nardell

mayuranki almaula Replied at 12:58 PM, 31 Mar 2017

Dear Dr Nardell,
I was not offering it for a clinical decision . He asked if there were any newer developments that could possibly offer some options.
We are not selling the tests, we are not there yet. We could just offer some data that shows that this test performs well enough to warrant comparison, just like you said more studies that can be approved and affordable .

Mayuranki

JEEWAN PANDEY Replied at 1:12 PM, 31 Mar 2017

Thank your Dr. Nardell and Dr. Almaula for your feedbacks. We soley do not depend on Mantoux test because like you said Dr. Nardell, they are not very sensitive as well as specific test for Pulmonary Tuberculosis. We depend upon clinical symptoms and signs along with other tests like I have mentioned in my question. My query is regarding any new tests that have been available recently. I hope this healthy dicussion will be very fruitful and informative.

Dr. Saleh, yes indeed the poorer countries like Nepal, Afghanistan and many others are heavily dependent on tests like Mantoux along with sputum examination and imaging like chest xrays besides clinical examinations. I hope the newer technologies will be readily available to poor countries in the days to come!

Regarding GeneXpert, though it is available in few centers in our country, its not as readily available as it is expected to be. At the same time, for the diagnosis of extra pulmonary Tuberculosis, it still is difficult and as per my experience, I still have not been able to know what are the tests modalities to look for!

Edward Nardell, MD Moderator Replied at 1:36 PM, 31 Mar 2017

Dear Mayuranki,
To quote you, "It will be possible for us to help you out with a CoDx box which includes a small portable machine that is based on magnetic induction. We also have a melt technology on this system that helps with our drug resistant panel for TB. We have a group based in India. Please let us know how to reach you"

Exactly why would you supply a clinician with a diagnostic tool if you do not intend for it to be used for clinical decision making?

Mark M.C. Replied at 5:26 PM, 5 Apr 2017

The same happens here in Latin America where we only have auxiliary tests such as Mantoux test, chest X-ray and a sputum exam for the diagnosis of pulmonary tuberculosis.

Donald Catanzaro Replied at 1:13 AM, 6 Apr 2017

Good Day Dr. Pandey,

For resource limited countries the MODS (microscopic-observation drug-susceptibility) assay is faster and cheaper than other culture-based tests currently in use for TB diagnosis.

MODS can be used as a drug susceptibility test and has been recommended for direct testing of sputum specimens by the WHO since 2011 (see Noncommercial Culture and Drug-Susceptibility Testing Methods for Screening Patients at Risk for Multidrug-Resistant Tuberculosis: Policy Statement available here https://www.ncbi.nlm.nih.gov/books/NBK131916/).

Our group has extended MODS from MDR-TB test to an XDR-TB test (see Second-line drug susceptibility breakpoints for Mycobacterium tuberculosis using the MODS assay available at https://www.ncbi.nlm.nih.gov/pubmed/24429318).

We later tested the MODS XDR-TB test in three countries (India, South Africa, Moldova) with quite good results against MGIT culture/DST. See Performance Comparison of Three Rapid Tests for the Diagnosis of Drug-Resistant Tuberculosis available at https://www.ncbi.nlm.nih.gov/pubmed/26322781.

MODS has been tested in many other countries (e.g. Peru, Mali, Boliva, India, China, Thailand) and there is a lot of literature out there on its performance.

Is it new? In a word "that depends" - MODS has been around for a while and it certainly is ready for use in a country such as yours!

Can it be used on "sputum negative samples"? That depends on if you mean smear negative or culture negative. Most tests out there will suffer performance differences depending on smear-culture results.

Interestingly our study showed that test failure when compared to MGIT culture/DST was different between the molecular tests (Hain LPA and Pyrosequencing) and MODS. By that I mean, some samples that failed in LPA worked in MODS while some samples that failed in MODS worked in LPA.

PS - You can perform MODS very cheaply (it is all open source!) but if you want to buy a "kit" there is a company (http://hardydiagnostics.com/) that sells MODS kits that detects Mtb and resistance to isoniazid and rifampicin.

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