Molecular Diagnosis of TB and MDR-TB in HIV-Coinfection in Nigeria
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CitationDinic, Lana. 2012. Molecular Diagnosis of TB and MDR-TB in HIV-Coinfection in Nigeria. Doctoral dissertation, Harvard University.
AbstractTuberculosis (TB) is the most common opportunistic infection in HIV-infected patients and the emergence of drug-resistant tuberculosis (DR-TB) is a growing problem in resource-limited settings (RLS). TB diagnosis in most RLS still depends on smear microscopy for acid-fast bacilli (AFB) while adequate infrastructure for testing drug sensitivity is unavailable. However, molecular diagnostics that detect Mycobacterium tuberculosis (Mtb) DNA and its genetic markers of drug resistance were recently developed. In this thesis I describe the use of a molecular diagnostic, Genotype MTBDRplus, for characterizing DR-TB and patterns of tuberculosis-like infection in two cities in south-west and north-central Nigeria. I found high rates of DR-TB in Nigerian HIV-infected individuals (9.3% for RIF or INH) with significantly different amounts by location (18.18% in south-west vs. 3.91% in north-central Nigeria, p=0.01). RIF resistance, indicative of MDR-TB, was found in 5.52% treatment-naïve patients, far exceeding the WHO predictions (0-4.3%). Furthermore, RIF resistance was genetically distinct, suggesting location-specific transmission of drug resistance (p=0.04). Genotype MTBDRplus correctly identified the drug-resistant samples compared to sequencing in 96.8% of cases. Mtb was confirmed in 56% of patients and was less likely to be found in patients on ART, while controlling for other relevant demographic characteristics (OR 0.29, P=0.02). Only abnormal respiratory findings on auscultation and the direct sputum smear grade greater than 3/100 were significant predictors of Mtb infection (OR 3.28, P=0.03; OR 6.40, p<0.01 respectively). Concentrated sputum smear was not significantly correlated with Mtb infection, except at the highest grades (>2+). Furthermore, in 49% of samples that were not confirmed for Mtb other actinomycetes were found: atypical Mycobacteria (ATM), Rhodococcus spp., Nocardia spp., Corynebacterium spp. I conclude that concentrated sputum AFB smears may misidentify bacteria as Mtb in a subset of HIV-infected patients. These individuals may have a different, even uncharacterized, actinomycete infection in the respiratory tract. Furthermore, total DR-TB in HIV-infection is high and transmission of DR-TB in HIV-infected patients in Nigeria is higher than estimated by the WHO. Molecular diagnostics are a rapid method for identifying Mtb and monitoring DR-TB, and can guide appropriate treatment decisions for respiratory infections in RLS with a high HIV burden.
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