Addressing the Threat of Drug-Resistant Tuberculosis A Realistic Assessment of the Challenge: Workshop Summary (2009) / Chapter Skim
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3 MDR TB Transmission, HIV Coinfection, and Transmission Control
3 MDR TB Transmission, HIV Coinfection, and Transmission Control
Pages 35-50
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From page 35... ...
Friedland suggested that the present situation, characterized by recent increases in MDR and XDR TB, illuminates past and current deficiencies in existing knowledge of TB, as well as the practices, programs, and strategies used to combat the disease. Areas with high TB and HIV rates threaten the success of both the Stop TB Partnership and historic antiretroviral rollout programs.
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From page 36... ...
TREATMENT Murray discussed the inadequacies of current TB treatment strategies and how these inadequacies lead to increases in drug resistance and transmission. She cited estimates that of the half million MDR TB cases and 40,000 XDR TB cases newly diagnosed in 2006, only a small proportion are being treated through either GLC-approved or non-GLC-approved treatment programs (see Figure 3-1)
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From page 37... ...
Murray discussed a study from the 1950s that exposed animals to labo ratory TB strains selected for resistance to isoniazid. The isoniazid-resistant strain was found to be less virulent than susceptible strains in the animals.
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From page 38... ...
Edward Nardell of Brigham and Women's Hospital stated that he and colleagues at the South African Medical Research Council and CDC have been researching the transmission of MDR TB from patients directly to sentinel guinea pigs to replicate and expand upon some of the early research of Richard Riley discussed by Murray. Although Nardell's group has observed higher rates of transmission than were reported in the past, rates of progression to active disease have been low.
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From page 39... ...
Gandhi stated that this latter mechanism has largely been neglected in the development of TB control programs. While acquired or amplified resistance due to inadequate treatment may explain how the very first cases of XDR TB emerged in South Africa and other parts of the world, it is difficult to say that the current magnitude of the epidemic could be attributable to acquired resistance alone.
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From page 40... ...
Genotyping, however, demonstrated that these two new XDR TB isolates resulted from new infections due to primary transmission, not acquired resistance to second-line therapy. Gandhi suggested that three important lessons should be learned from these findings: • Efforts must focus on creating infection control programs to prevent the further transmission of drug-resistant strains.
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From page 41... ...
Image B shows the genotypes of initial susceptible isolates and the follow-up XDR TB isolates for 10 patients. All 17 patients had different genotypes in their relapse isolates compared with their initial isolates.
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From page 42... ...
Drug-susceptible strain MDR TB strain Two XDR TB strains FIGuRE 3-4 Four TB strains in a single patient. SOURCE: Andrews et al., 2008.
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From page 43... ...
(Information on the current situation in Shanghai, China, presented by Qian Gao of Shanghai Medical College, is provided in Box 3-1.) MITIGATING TRANSMISSION Nardell stated that, given a setting with appropriate resources for transmission control strategies and more effective treatment, it is possible to cure and control the spread of MDR TB.
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From page 44... ...
. However, implementing effective transmission control in resource-limited settings globally presents major challenges: • Establishing community-based treatment outside a hospital cur rently is not feasible in some settings because the tradition and infrastructure for community care do not exist.
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From page 45... ...
As mentioned earlier, between 1985 and 1992 there was a somewhat focal MDR TB epidemic in the United States. Studies showed that MDR TB was being spread in hospitals, jails, prisons, homeless shelters, and residential AIDS facilities, among other congregate settings where both HIVpositive and -negative persons were exposed.
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From page 46... ...
The strategy is imperfect for several reasons: sputum smear-positive patients can transmit their disease, smear-positive patients in the TB pavilion can reinfect one another, and unsuspected cases pose a threat. Compared with current conditions, however, this baseline strategy could be highly effective if adapted and widely implemented in settings where no transmission control currently exists.
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From page 47... ...
air disinfection; the TB ward has natural ventilation with fenestrated brick and more UV fixtures to disinfect the air than the general ward has; the six isolation rooms are off a common corridor, and each has a large exhaust fan built into the 3-5 that draws air into the room from the corridor, as well Figure wall as a UV fixture. R01436 SOURCE: Nardell, 2008.
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From page 48... ...
New research is under way on several novel interventions to enhance transmission control: • Nardell stated that installation of upper-room UV air disinfection in a hospital and TB/HIV ward in Lima has been shown to reduce transmission by 72 percent. Additional experiments with upper room UV disinfection are being conducted at an MDR TB hospital in South Africa, with sentinel guinea pigs being used to determine whether the intervention is effective in preventing transmission.
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From page 49... ...
Among health care workers involved in treating those afflicted by the XDR TB epidemic, there were four in whom XDR TB was suspected; all four were HIV infected, and all four died with a rapid course similar to that of the 53 patients. Since the initial cases were described, additional health care workers have been infected with both MDR and XDR TB.
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