If we set it up in a rural setting with a very high HIV and TB burden?
The advantage of GeneXpert is that it will give identification of MTB and resistance to RIF in two hours; it can be operated with minimal training, and biohazzard risk is even less than that associated to microscopy. The equipment and cartridges costs have been dramatically reduced and the maintenance costs that used to be astronomical are now very affordable. If a patient has a positive test for RIF (and sensitivity of the newer cartridges has been upgraded) the patient should not be started in Category I regimen and should be tested for full first line drugs resistance (most of those with RIF resistance will also be resistant to INH); this will reduce the probability of extending drug resistance in a given case. The MODS assay is an alternative for costly DST (for example MGIT); it takes about a week, has a potential of biohazzard and requires trained personal and laboratory facilities
Dear Rafael,
Thanks a lot for your commentaries. I agree GeneXpert looks amazing. Nevertheless there are some drawbacks.
First, production is dependent on only one company and they are having some trouble to supply all the worldwide need.
Second, costs are still very high, they are only reduced due to subventions and for certain countries. Real cost is as expensive as MGIT. And funding is not going to last forever...Compared to MODS that has a cost of 2 USD per test once everything is setup. MODS looks much more sustainable although the initial investment is maybe higher than investment for a subventioned GeneXpert, but not for a real cost GeneXpert...
Third, diagnostic test accuracy for MODS is clearly superior to GeneXpert and especially for HIV positive patients.
I personally believe that MODS is more expensive and more difficult to setup than GeneXpert ,but in the long run much more sustainable.
Any other opinion?
Dear Philip, sorry for the late to your question. The best way to diagnose TB is whatever works in your context!!! However,although we have the opportunity to maximize new technologies (G-Xpert and MODS) neither these diagnostic methods would not do the job Sputum microscopy does. The best way to diagnose TB is use LED-FM microscopy for pulmonary TB with have well trained lab-techs. For MDR-TB diagnosis, a combined method of G-Xpert and MODS. MODS will help you diagnose Isoniazid resistance. G-Xpert will help you tell 3 things: 1. if the person has TB, 2. TB has a resistant strain, and 3. whether the resistant is to Rifompicin. But really the key is whether the Lab-techs know what they are doing in all areas of lab-work (sputum collection, processing, examination and quantification). So, we need to focus not so much on technologies but knowledge and skills of lab-techs.
Hope that helps, and sorry for the long comment.
Halima
TB control program in a country if include this as a policy, and bear the cost then you people think G-Xpert is better option for MDR TB ?
Every Rif resistance result diagnosed by GeneXpert ahs to be confirmed by culture, and the Positive predictive value is highly dependent on the prevalence of MDR-TB in your context. The usefulness of GeneXpert for the diagnose of MDR-TB has to be cautiously interpreted.
Hi Philip, what test did you set up in the rural area? Any recommendation? Thanks
We arrived to the conclusion that GeneXpert was the most cost-effective technique.
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