Time-to-Detection in Culture of M. tuberculosis: performance for assessing index cases contact-positivity.

Publication date: Jul 09, 2023

Time-to-Detection (TTD) in culture on liquid media is inversely correlated to bacillary load and should be a contributing factor for assessing tuberculosis transmission. We wanted to assess if TTD was a better alternative than smear-status to estimate transmission risk. From October 2015 to June 2022, we studied retrospectively a cohort of index cases (IC) with pulmonary tuberculosis (tuberculosis disease TD) from which samples were was culture-positive before treatment. We studied the correlation between TTD and contact-positivity of IC-contacts: contact positivity cp, was defined as cp=1 (CP group) in case of TD or LTI (latent tuberculosis infection) in at least one screened contact of an IC, and cp=0 otherwise (CN group). Univariate and multivariable analysis (logistic regression) were done. Of the 185 IC, 122 were included, generating 846 contact-cases of which 705 were assessed. A transmission event (LTI ot TD) was identified in 193 contact-cases (transmission rate: 27%). At Day 9, 66% and 35% of the IC had their sample positive in culture for CP and CN groups respectively. Age and TTD ≤ 9 days were independent criteria of CP (OR 0. 97, CI [0. 95 – 0. 98], p=0. 002 and OR 3. 52, CI [1. 59 – 7. 83], p=0. 001, respectively). TTD was a more discriminating parameter than smear-status to evaluate transmission risk of an IC with pulmonary tuberculosis. Therefore, TTD should be considered in the contact-screening strategy around an IC.

Concepts Keywords
Cohort contact-screening
June index cases
Td Mycobacterium tuberculosis
Tuberculosis smear-status


Type Source Name
disease MESH latent tuberculosis infection
disease MESH pulmonary tuberculosis
drug DRUGBANK Tropicamide
pathway KEGG Tuberculosis
disease MESH tuberculosis

Original Article

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