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Current time:0:00Total duration:8:43

Video transcript

this is Charles prober and Morgan theis and for this video we're going to talk about resistance among TB infections so resistance drug resistance a very important topic because it dramatically affects how we treat different patients and the timeline and the patient that Morgan has drawn is going to help us describe different scenarios about how to treat patients who have different kinds of TB in terms of the resistance pattern and so this little person we've diagnosed as having a TB infection based upon their clinical presentation and some of the laboratory tests we did which we talked about in another video and when the patient starts their therapy especially if they're in the developing world where the expert RIF test is available that's that molecular test that we described in another video that identifies that TB is present it's on a molecular assay and that that particular TB is resistant to refampin if that's the case then that's going to immediately modify how we treat this patient with their TB infection but let's assume that the expert test is negative okay and we have a TB infection that we've diagnosed we take cultures of the sputum and we know that those cultures are going to come back in four weeks or six weeks takes a bit of time and those cultures are also going to be tested the bacteria are going to be tested for sensitivity to the anti tuberculous agents but we're not going to have that information out for about six weeks because that's how long it takes a TB to grow okay so here's my little culture plate that's trying to grow out that sputum perfect so while we're waiting for the culture results in sensitivity testing to come back we need to start therapy for this TB infection and the standard therapy is using all of the first-line drugs that you've listed in the top hand corner that we referred to before as ripe the refampin isin ayazad pira's in amide and ethambutol okay refampin and ni zijn eyes eyed or i and h are used for a full six months if this turns out to be a sensitive TB bug so they're both used for six months the peer is in amide and ethambutol are used for the first two months of that six-month interval so that's the standard therapy now let's consider we've got the culture results that have come back from that sputum and we're six weeks into this treatment and we discover from those culture results that the organism the TB is resistant to one of our TB agents the most common resistance would be two inh but they can be resistant to any of the different first-line drugs if the organism turns out to be resistant dye NH we will stop the inh because it won't do much good and we'll either just continue the three drugs for a longer period of time or we may add a fluoroquinolone if the TB turns out to be resistant to refampin based upon that sensitivity testing will stop the rifampin and may continue the other three drugs and maybe even add something like streptomycin so the idea here is that if whatever drug this particular TB organism is resistant to you're going to stop using it and you're going to continue with the other ones you may consider adding a secondary drug and you might consider a longer treatment all correct yes so if the bugs are resistant the TB is resistant to both inh and refampin the term that is used for that resistance is MDR which stands for multiple drug-resistant TB and these are becoming increasingly important around the world it turns out that the countries that have the most MDR isolates are five countries in the world and those include China India Pakistan the Russian Federation countries and South Africa so that's only five countries and they have the largest amount of MDR TV TB the final type of resistant TB that I would like to mention is called xdr-tb which stands for extreme drug-resistant and XDR TB is less common than MDR TB but more serious because it's harder to treat because they're resistant to multiple drugs that are either first slide anti TB drugs or second-line which you also put in the right-hand corner of this picture they're more difficult to treat and in fact the mortality rate for these xdr-tb is much higher but let's assume that we do the sensitivity testing at when the sputum comes back positive at six weeks or so and they turn out to be sensitive and we're continuing on with just a standard ripe therapy but then as we're checking the sputum cultures as we want to do on a regular basis when you get up to three months it turns out the sputum culture is still positive it should not be still positive you should have a negative sputum culture by about two months or so or even earlier because we've been treating the TB exactly so if it's still positive there's one of two possibilities one is the TB has developed resistance to one of the anti tuberculosis in which case you'll have to modify therapy and you'll know it's resistant because you tested sensitivity again the other possibility is it's just a slow responder that the patient continues to have positive sputum z' even though the bugs are sensitive are killed by the drugs or the antibiotics you're using and it's just slow under either circumstance therapy you'll have to anticipate modifying therapy if it's resistant you'll change the ante tuberculous agents and treat the patient longer if it's sensitive you'll just anticipate treating the patient longer than the standard six months then the final scenario that I would like to mention is all goes well for the six months of therapy the patient's chest x-ray gets better they look well and you believe you have cured the infection okay so here at six months all is good my patient is is happy exactly and cured supposedly but the scenario that I'll now describe is several months or even years later that happy patient becomes sad again because the patient has a relapse of the infection the signs and symptoms of TB reappear now that may be because the patient's initial infection was never completely eradicated and it just came back or it may be that the patient acquired a new TB infection from somebody else so it's a completely different TB infection so it's not really relapse in that case it's reinfection but nonetheless the symptoms have relapsed so how could you tell the difference if a patient who is treated for their original TB then years later presented with TB again how could you tell if it was a relapse of their original bug or a new infection with a new bug so that's a great question and the only way you'd be able to tell the difference is if you had both TB bugs in your laboratory available to retest and you can do molecular testing on the two bugs and see if their DNA is the same or different if the DNA is the same then it's a relapse because it's the same bug if the DNA is different then it's a reinfect oh great so you really can figure that out exactly