Time discrepancy for tuberculosis-negative microscopy and culture - the diagnostic gap remains: systematic analysis...

Patients with open pulmonary tuberculosis (opTB) are subject to strict isolation rules. Sputum smear microscopy is used to determine infectivity, but sensitivity is lower than for culture. This study aimed to investigate the clinical relevance of this mismatch in contemporary settings.

Differential results between microscopy and culture were determined at the time of microscopic sputum conversion, from all patients with opTB between 01/2013 and 12/2017. In addition, data on HIV, multi/extensive drug-resistant TB status, time to smear- and cultural-negativity conversion were analyzed; and a Kaplan-Meier curve was developed.

Of 118 patients with opTB, 58 had demographic data available for microbiological and clinical follow-up analysis; among these, 26 (44.8%) had still at least one positive culture result. Median time from opTB-treatment initiation to full microscopic sputum- or culture conversion, was 16.5 days (range 2-105), and 20 days (1-105), respectively (median difference: +3.5 days). Sixteen days after de-isolation, >90% had converted culturally. HIV- or multi/extensive drug-resistant TB status did not impact conversion time.

When patients with opTB were de-isolated after 3 negative sputum smear microscopy tests, a substantial part still revealed cultural growth of Mycobacterium tuberculosis complex, but it remains unclear, whether smear-negative and culturally-positive individuals on therapy are really infective. Thus, the clinical relevance of this finding warrants further investigation.