Evaluation of four molecular methods for the diagnosis of tuberculosis in pulmonary and blood samples from immunocompromised patients

The present study analysed the concordance among four different molecular diagnostic methods for tuberculosis (TB) in pulmonary and blood samples from immunocompromised patients. A total of 165 blood and 194 sputum samples were collected from 181 human immunodeficiency virus (HIV)-infected patients with upper respiratory complaints, regardless of suspicious for TB. The samples were submitted for smear microscopy, culture and molecular tests: a laboratory-developed conventional polymerase chain reaction (PCR) and real-time quantitative PCR (qPCR) and the Gen-Probe and Detect-TB Ampligenix kits. The samples were handled blindly by all the technicians involved, from sample processing to results analysis. For sputum, the sensitivity and specificity were 100% and 96.7% for qPCR, 81.8% and 94.5% for Gen-Probe and 100% and 66.3% for Detect-TB, respectively. qPCR presented the best concordance with sputum culture [kappa (k) = 0.864)], followed by Gen-Probe (k = 0.682). For blood samples, qPCR showed 100% sensitivity and 92.3% specificity, with a substantial correlation with sputum culture (k = 0.754) and with the qPCR results obtained from sputum of the corresponding patient (k = 0.630). Conventional PCR demonstrated the worst results for sputa and blood, with a sensitivity of 100% vs. 88.9% and a specificity of 46.3% vs. 32%, respectively. Commercial or laboratory-developed molecular assays can overcome the difficulties in the diagnosis of TB in paucibacillary patients using conventional methods available in most laboratories.

High frequency of resistance to the drugs isoniazid and rifampicin among tuberculosis cases in the city of Cabo de Santo Agostinho, an urban area in Northeastern Brazil

The objective of the present study was to investigate the frequency and risk factors for developing multidrug-resistant tuberculosis in Cabo de Santo Agostinho, PE. This was a prospective study conducted from 2000 to 2003, in which suspected cases were investigated using bacilloscopy and culturing. Out of 232 confirmed cases of tuberculosis, culturing and antibiotic susceptibility tests were performed on 174. Thirty-five of the 174 cultures showed resistance to all drugs. The frequencies of primary and acquired resistance to any drug were 14 percent and 50 percent respectively, while the frequencies of primary and acquired multidrug resistance were 8.3 percent and 40 percent. Previous tuberculosis treatment and abandonment of treatment were risk factors for drug resistance. The high levels of primary and acquired resistance to the combination of isoniazid and rifampicin contributed towards the difficulties in controlling tuberculosis transmission in the city.

O objetivo do presente estudo foi investigar a freqüência e fatores de risco para o desenvolvimento de tuberculose multidroga resistente, na Cidade do Cabo de Santo Agostinho, PE. Este é um estudo prospectivo realizado entre 2000-2003 onde casos suspeitos foram investigados por baciloscopia e cultura. De 232 casos de tuberculose confirmados, 174 tiveram cultura e antibiograma realizados. Trinta e cinco das 174 culturas mostraram resistência a qualquer uma das drogas. A freqüência de resistência primária e adquirida a qualquer droga foi 14 por cento e 50 por cento respectivamente enquanto a freqüência primária e adquirida para multidroga resistência foi 8,3 por cento e 40 por cento. Tratamento prévio para tuberculose ou abandono de tratamento consistiu em fatores de risco para resistência a drogas. Os altos níveis de resistência primária e adquirida a combinação isoniazida e rifampicina contribuem para as dificuldades no controle da transmissão da tuberculose no Cabo.