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Selection bias in multidrug-resistant tuberculosis cohort studies assessing sputum culture conversion | Journal Article / Research | MSF Science Portal
Journal Article
|Research

Selection bias in multidrug-resistant tuberculosis cohort studies assessing sputum culture conversion

Rodriguez CA, Lodi S, Horsburgh CR, Bastard M, Hewison C, Huerga H, Khan M, Khan PY, Khan U, Oyewusi L, Padayachee S, Mitnick CD, Franke MF

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Abstract

BACKGROUND


Conversion of sputum culture from positive to negative for M. tuberculosis is a key indicator of treatment response. An initial positive culture is a pre-requisite to observe conversion. Consequently, patients with a missing or negative initial culture are excluded from analyses of conversion outcomes. To identify the initial, or “baseline” culture, researchers must define a sample collection interval. An interval extending past treatment initiation can increase sample size but may introduce selection bias because patients without a positive pre-treatment culture must survive and remain in care to have a culture in the post-treatment interval.


METHODS


We used simulated data and data from the endTB observational cohort to investigate the potential for bias when extending baseline culture intervals past treatment initiation. We evaluated bias in the proportion with six-month conversion.


RESULTS


In simulation studies, the potential for bias depended on the proportion of patients missing a pre-treatment culture, proportion with conversion, proportion culture positive at treatment initiation, and proportion of patients missing a pre-treatment culture who would have been observed to be culture positive, had they had a culture. In observational data, the maximum potential for bias when reporting the proportion with conversion reached five percentage points in some sites.


CONCLUSION


Extending the allowable baseline interval past treatment initiation may introduce selection bias. If investigators choose to extend the baseline collection interval past treatment initiation, the proportion missing a pre-treatment culture and the number of deaths and losses to follow up during the post-treatment allowable interval should be clearly enumerated.


Subject Area

tuberculosis

Collections

The endTB project

Languages

English
DOI
10.1371/journal.pone.0276457
Published Date
10 Nov 2022
Journal
PLOS One
Volume | Issue | Pages
Volume 17, Issue 11, Pages e0276457
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