Caracterización clínica y microbiológica de pacientes con trazas en Xpert MTB/RIF Ultra / Clinical and microbiological characterization of patients with Xpert MTB/RIF Ultra traces

INTRODUCCIÓN: El Xpert MTB/RIF Ultra (Ultra) ha mejorado dramáticamente el diagnóstico de la tuberculosis (TBC). Con él ha nacido la categoría de trazas, que es la menor carga bacilar detectable por este examen. OBJETIVO: Describir las características clínicas de los pacientes con presencia de trazas en el Ultra y evaluar la confirmación de la TBC como diagnóstico clínico. MATERIALES Y MÉTODOS: Estudio descriptivo de serie de casos. Se extrajo la información de fichas clínicas de pacientes con positividad a trazas. Se confrontaron datos clínicos, microbiológicos e histopatológicos. RESULTADOS: Se analizaron 21 pacientes. La edad promedio fue de 52 años. Todos los casos presentaron baciloscopias negativas. Cuatro cultivos en medio líquido MGIT fueron positivos, dos en pleura parietal, uno en líquido pleural y otro en expectoración. En pleura parietal, tres casos presentaron granulomas con necrosis caseosa y un granuloma esbozos de necrosis. En tejido pulmonar se observaron dos casos con granulomas con esbozos de necrosis y dos con granulomas no necrotizantes. Tres pacientes tenían el antecedente de TBC previa, se interpretó la positividad de trazas en ellos como falsos positivos. Finalmente se diagnosticaron 13 casos como TBC activa, donde cinco de ellos fueron TBC pleurales. La mayor concordancia clínica, microbiológica e histopatológica fue en muestras de líquido y tejido pleural. DISCUSIÓN: Se debe interpretar con cautela los hallazgos de esta prueba en muestras de vía aérea; el análisis multidisciplinario (clínica, imágenes, microbiología, histología) es crucial en las decisiones de nuestras conductas clínicas futuras. El hallazgo de trazas en pleura tiene, a nuestro parecer, un alto valor diagnóstico en el estudio de la tuberculosis en esta localización.

INTRODUCTION: Xpert MTB/RIF Ultra has dramatically changed the diagnosis of tuberculosis. A new category called traces appeared, which is the smallest amount of bacillar load detectable. OBJECTIVE: Describe the clinical characteristics of patients that present traces in Xpert MTB/RIF Ultra test, and to evaluate the confirmation of tuberculosis as clinical diagnosis. METHODS: We perform a descriptive case series study. Information was recovered from clinical records of patients with positive test for traces. Clinical, histopathological and microbiological results were confronted. RESULTS: Twenty one patients were analyzed. The mean age was 52 years-old. All cases had negative smear microscopy and four MGIT cultures were positive, two in pleural fluid and another in sputum. In parietal pleura, three cases presented granulomas with caseous necrosis, and one showed granuloma with very little necrosis. In pleural tissue we observed two cases of granulomas with traces of necrosis and two with non-necrotizing granulomas. Three patients had history of previous tuberculosis and positive traces, the test was interpreted as a false positive result. Finally, active tuberculosis was diagnosed in 13 cases, and five of them were pleural tuberculosis. The highest clinical, microbiological and histopathological agreement was in fluid and pleural tissue samples. DISCUSSION: The findings of Xpert MTB/RIF Ultra in airway samples must be interpreted carefully. Multi-disciplinary analysis is crucial in future clinical decisions. The finding of traces in pleura has, in our opinion, a high diagnostic value in the study of tuberculosis in this location.

Preanalytical conditions can interfere with M. tuberculosis detection by PCR in respiratory samples

OBJECTIVES: Tuberculosis is one of the most prevalent infections in humans. Although culture is the reference for diagnosis, its sensitivity is compromised, especially in paucibacillary samples. Because polymerase chain reaction (PCR) amplifies mycobacterial DNA, it is more sensitive than culture for the diagnosis of Mycobacterium tuberculosis (Mtb). However, its performance can be affected by intrinsic sample inhibitors and by the extraction/detection techniques used. METHODS: We evaluated the influence of preanalytical conditions on Mtb detection in samples of sputum (SPU), bronchoalveolar lavage (BAL), and pleural fluid (PF) using combinations of extraction/detection methods. Respiratory samples were prepared to contain different concentrations of red blood cells and nucleated cells to which increasing amounts of Mtb colonies were inoculated and submitted to PCR. RESULTS: Up to 102 CFU/ml of Mtb were detected in the SPU in all methods, except for the Roche extraction/detection method, regardless of the preanalytical sample condition. In BAL samples, medium and high concentrations of cells and high concentrations of red blood cells contributed to a lower Mtb detection, regardless of the extraction method used. In PF, red blood cells were the variable that most interfered with Mtb detection, with better recovery (102 CFU/ml) observed with the Qiagen/Nanogen combination. CONCLUSION: The choice of Mtb extraction and detection method is of fundamental importance for PCR analytical sensitivity, especially when paucibacillary samples and/or samples containing potential PCR inhibitors are analyzed.

Avaliaçäo de modificaçöes na rotina laboratorial do líquido pleural no rendimento diagnóstico de tuberculose pleural / Evaluation of laboratory routine of pleural fluid in diagnostic yield for pleural tuberculosis

Foi comparado o rendimento diagnóstico de tuberculose obtido em estudo propesctivo do líquido pleural de 80 pacientes e em análise retrospectiva de 105 prontuários médicos. Na série prospectiva foi introduzido o controle de qualidade, quando atençäo especial foi dada à colheita, transporte e processamento (precedido ou näo de descontaminaçäo) do líquido pleural. Na série retrospectiva utilizou-se a rotina do Serviço de Bacteriologia da Tuberculose, que consistia em descontaminaçäo de todos os materiais. Na abordagem prospectiva, 97 por cento dos pacientes tiveram seu diagnóstico confirmado. Este foi obtido histopatologicamente em 87 por cento e bacteriologicamente em 56 por cento dos casos. No estudo retrospectivo, a confirmaçäo diagnóstica ocorreu em 94 por cento dos casos. Na série prospectiva, a sensibilidade da cultura no líquido pleural näo precedida de descontaminaçäo (36 por cento) foi superior àquela observada no material submetido a descontaminaçäo (29 por cento) (p = 0,02). O rendimento da cultura do líquido pleural submetido a descontaminaçäo foi de 29 por cento e o oservado no exame bacteriológico do fragmento pleural, de 42 por cento (p < 0,02). Entretanto, na ausência de descontaminaçäo, o rendimento bacteriológico do líquido pleural (36 por cento) e o do fragmento pleural (42 por cento) foram semelhantes (p = 0,22). O controle de qualidade introduzido na série prospectiva aumentou o rendimento da cultura do líquido pleural de 26 por cento para 29 por cento.