# Factors predicting 2-month culture positivity in smear-positive pulmonary tuberculosis

Mickael Manchon, Mallorie Kerjouan, Delphine Bachelet, Stéphane Jouneau, Charles Ricordel, Cédric Laouénan, Nathalie de Castro, Pierre Tattevin

<figure><img src="image_1.png" /></figure>

## To cite this version:

Mickael Manchon, Mallorie Kerjouan, Delphine Bachelet, Stéphane Jouneau, Charles Ricordel, et al. "Factors predicting 2-month culture positivity in smear-positive pulmonary tuberculosis. Infectious Diseases Now, 2025, 56 (1), pp.105220. 10.1016/j.idnow.2025.105220. hal-05399959

HAL Id: hal-05399959

https://hal.science/hal-05399959v1

Submitted on 7 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
Original article

# Factors predicting 2-month culture positivity in smear-positive pulmonary tuberculosis

Mickael Manchon<sup>a,*</sup>, Mallorie Kerjouan<sup>a</sup>, Delphine Bachelet<sup>b</sup>, Stéphane Jouneau<sup>a,c</sup>, Charles Ricordel<sup>a</sup>, Cédric Laouenan<sup>b</sup>, Nathalie De Castro<sup>d</sup>, Pierre Tattevin<sup>e</sup>

Check for
updates

## ARTICLE INFO

**Keywords:**

Cough

Sputum

Culture

Prolonged treatment

## ABSTRACT

**Introduction:** Failure to achieve sputum culture conversion after two months of treatment (M2) for pulmonary tuberculosis (TB) is associated with treatment failure. We aimed to identify the determinants of persistent culture-positive sputum at M2.

**Methods:** We performed an ancillary study of the multicentric randomized trial FAST-TB, which enrolled adult patients with smear-positive rifampicin-susceptible pulmonary TB in France in 2014–2018.

**Results:** Among the 203 patients enrolled in the FAST-TB study, 177 were evaluated at M2, including 104 with sputum culture: 82 (79 %) culture-negative, and 22 (21 %) culture-positive. Persistence of cough and sputum during follow-up was associated with culture positivity at M2: This was significant for sputum at different time points (respectively 84 % in culture-positive vs. 50 % in culture-negative at M1, 65 % vs. 37 % at M2, and 43 % vs. 17 % at M4, P < 0.05 for all), and for persistent cough at M4 (71 %, vs. 36 %, P = 0.006). Treatment success was similar between groups.

**Conclusion:** The main predictors of culture-positive sputum at M2 in patients with smear-positive rifampicin-susceptible pulmonary TB are persistent cough and sputum during treatment. Systematic monitoring of these symptoms could contribute to early detection of patients who may require prolonged anti-TB treatment.

## 1. Introduction

Tuberculosis (TB) is a major public health issue, with an estimated 10.8 million new cases, and 1.25 million deaths worldwide in 2023 [1].

In most countries, the standard treatment for rifampin-susceptible pulmonary TB relies on a four-drug regimen with rifampicin, isoniazid, pyrazinamide, and ethambutol during the first two months followed by rifampicin and isoniazid for four months [2,3].

Conversion of sputum cultures at two months of treatment (M2) is the most widely recognized predictive factor of treatment success [4–10]. Previous studies found that cavitary lesions [11–17], extensive pulmonary parenchymal involvement [13,18,19] and high density of acid-fast bacilli (AFB) on microscopic examination (ME) at diagnosis were associated with failure to sterilize sputum at M2 [11,13,16,17,19–21].

The American Thoracic Society (ATS) recommends that in patients with culture-positive sputum at M2, susceptibility testing to anti-TB drugs be repeated on bacilli isolated at M2, and that the consolidation two-drug therapy be extended by three months, for a total duration of nine months [2,3,22].

Baseline and on-treatment clinical variables that would contribute to early identification of patients at risk of persistent culture-positive sputum at M2 could be used to implement specific interventions in these patients, including anti-TB treatment intensification or prolongation, adherence reinforcement, and strengthened respiratory isolation procedures. We aimed to evaluate the prevalence and determinants of culture-positive sputum at M2, in patients with smear-positive pulmonary TB. Performed an ancillary study nested within the FAST-TB randomized controlled trial [23].

<footnote><sup>a</sup> Service de pneumologie, CHU Rennes, Rennes, France</footnote>

<footnote><sup>b</sup> AP-HP Hopital Bichat-Claude Bernard, Paris, France</footnote>

<footnote><sup>c</sup> Université de Rennes, CHU Rennes, Inserm, EHESP, Irset (Institut de recherche en santé, environnement et travail) – UMR_S 1085, France</footnote>

<footnote><sup>d</sup> Département de maladies infectieuses et tropicales, Lariboisière Saint-Louis, APHP, France</footnote>

<footnote><sup>e</sup> Service de maladies infectieuses et tropicales, CHU Rennes, Rennes, France</footnote>

<footnote>* Corresponding author at: CHU Rennes, 2 rue Henri Le Guilloux, 35000 Rennes, France.</footnote>

<footnote>E-mail address: mickael.manchon@gmail.com (M. Manchon).</footnote>
## 2. Material and Methods

### 2.1. Study design and procedures

Our study is a post-hoc analysis of the FAST-TB randomized trial, which demonstrated the non-inferiority of early discontinuation of ethambutol, in patients with rifampicin and isoniazid-susceptible pulmonary TB documented by PCR, compared to the standard initial four-drug regimen [23]. In brief, patients with AFB positive pulmonary TB were enrolled between September 2014 and January 2018 across 34 centers in France. Sputum specimens were cultured at M2 and at the end of treatment. Patients were prescribed a fixed-dose combination (Rifater®) of isoniazid (3–5 mg/kg/d), rifampicin (8–12 mg/kg/d), pyrazinamide (25–30 mg/kg/d) with or without ethambutol (15–20 mg/kg/d).

For this post-hoc analysis, we included all participants with data available at M2. Participants who provided sputum for culture were categorized in two groups: culture-negative (C-M2) and culture-positive (C + M2).

All participants provided written informed consent. The protocol was approved by the National French Ethics committee (IDRCB2013-A01406-39) and registered in [ClinicalTrials.gov (NCT # 02231229).](https://ClinicalTrials.gov)

### 2.2. Collected data

Data collected included sociodemographic factors, comorbidities, smoking status, body mass index [BMI], tuberculosis characteristics (clinical, microbiology, imaging), and treatment outcomes. Bacteriological cure was defined by two negative sputum cultures, including one during the last month of treatment, and treatment success defined by clinical response with complete treatment without bacteriological criteria, in line with the WHO definitions [24].

Symptom severity was assessed using the Teeter score, a composite clinical score ranging from 0 to 24, based on six tuberculosis-related symptoms (cough, sputum production, chest pain, dyspnea, wheezing, and WHO performance score) each rated from 0 (absent) to 4 (severe).

We further examined the characteristics associated with culture-positive sputum at M2, including data collected on visits scheduled at two weeks (W2), one month (M1), M2, M4, M6, M12, M18, and M24.

### 2.3. Additional analyses compared to the initial study design

We compared patients who did not attend the M2 consultation with those who did. Additionally, among patients who attended the M2 consultation, we compared those who had no sputum culture sampled at M2 to those with culture-negative sputum.

### 2.4. Statistical analysis

The variables were presented using descriptive statistics for the entire population. Proportions were used for qualitative data, and medians with interquartile ranges (IQR) were used for quantitative data. Patients with C-M2 and C + M2) were compared using the Wilcoxon test, and Pearson's Chi-squared test with Yates' continuity correction, as appropriate. A P-value < 0.5 was considered significant.

## 3. Results

Among the 203 participants included in the FAST-TB study, 177 (87 %) attended the M2 visit, of whom 105 (52 %) provided sputum for culture, including one with a non-contributive sample. Within these 104 cultures available at M2, 82 (79 %) were negative and 22 (21 %) were positive (Fig. 1).

The study population was predominantly male (72 %), with a median age of 38.5 years (IQR 30.8–49) and 58/104 (56 %) participants were from Sub-Saharan Africa. Cough was present in 94 % (96/104 patients), 51 % (53/104) reported dyspnea, and 30 % (31/104) had fever. Median BMI was 19.7 kg/m² (IQR 17.3–21.7) and 34 % (35/104) had BMI < 18.5 kg/m². The main comorbidities were diabetes (9/104, 9 %) and HIV (6/104, 6 %). Baseline characteristics were similar in C-M2 and C + M2 patients (Table 1).

Most patients (99 %) had abnormal chest X-ray, with bilateral lesions in 48/104 (46 %), and cavitary disease in 70/104 (67 %). Pulmonary TB was diagnosed on sputum samples in 97/104 (93 %). The baseline resistance rate was similar in C-M2 and C + M2 (10 % vs 10.5 %).

During treatment, the proportion of participants with persistent cough was numerically higher in the C + M2 group than in the C-M2 group at S2, M1, M2, and M4, but the difference was statistically significant only at M4 (Table 2, Fig. S1). The proportion of patients with persistent sputum production was higher at M1, M2, and M4 in the C + M2 group (respectively 84 % in culture-positive vs. 50 % in culture-negative at M1, 65 % vs. 37 % at M2, and 43 % vs. 17 % at M4, P < 0.05 for all, Table 3, Fig. S2). More patients had fever at M4 in the C + M2 group, 12 % (2/22) vs 0/82 (0 %), P = 0.04 (Table S1).

Treatment success was achieved in 95/104 (91 %) participants overall: 76/82 (93 %) for C-M2 patients and 19/22 (86 %) for C + M2 (P = 0.349) (Tables 4 and S2). There was no significant difference in total treatment duration (Table S3) or in the proportion of participants attending follow-up visits. Treatment prolongation after six months tended to be more common in the C + M2 group: 11/22 (50 %) vs. 22/78 (28 %), P = 0.0548.

Among participants not evaluated at M2 visit (n = 26, Table S4), 18/26 (69 %) had bilateral radiological involvement compared to 80/169 (47 %) in those evaluated at M2 (P = 0.021). Treatment failure was more common in patients not evaluated at M2: 14/26 (54 %) vs. 20/177 (11 %), P < 0.001.

<figure><img src="image_3.png" /><figcaption>Fig. 1. Flow chart.</figcaption></figure>
<caption>**Table 1**</caption>

Baseline characteristics of the 104 patients with sputum culture at 2 months (M2).

<table><thead><tr><th></th><th>Total (N = 104)</th><th>C-M2 (N = 82)</th><th>C + M2 (N = 22)</th></tr></thead><tbody><tr><td>Randomization arm: treatment without ethambutol</td><td>55 (53%)</td><td>42 (51%)</td><td>13 (59%)</td></tr><tr><td>Male</td><td>75 (72%)</td><td>60 (73%)</td><td>15 (68%)</td></tr><tr><td>Median age (years)</td><td>38.5</td><td>38.5</td><td>40</td></tr><tr><td>Patient (or a parent) from an endemic tuberculosis zone</td><td>76 (73%)</td><td>63 (77%)</td><td>13 (59%)</td></tr><tr><td>Region of origin: Africa</td><td>58 (76%)</td><td>48 (76%)</td><td>10 (77%)</td></tr><tr><td>Comorbidities</td><td></td><td></td><td></td></tr><tr><td>HIV infection</td><td>6 (6%)</td><td>5 (6%)</td><td>1 (5%)</td></tr><tr><td>Positive for hepatitis B virus surface antigen</td><td>5 (6%)</td><td>5 (6%)</td><td>0 (0%)</td></tr><tr><td>Positive for hepatitis C virus antibodies</td><td>4 (4%)</td><td>2 (2%)</td><td>2 (10%)</td></tr><tr><td>Diabetes</td><td>9 (9%)</td><td>7 (9%)</td><td>2 (9%)</td></tr><tr><td>Kidney failure</td><td>1 (1%)</td><td>0 (0%)</td><td>1 (5%)</td></tr><tr><td>Cancer / Solid tumor</td><td>2 (2%)</td><td>1 (1%)</td><td>1 (5%)</td></tr><tr><td>Smoking</td><td></td><td></td><td></td></tr><tr><td>Never smoker</td><td>44 (42,3%)</td><td>35 (43%)</td><td>9 (41%)</td></tr><tr><td>Former smoker</td><td>16 (15,4%)</td><td>13 (16%)</td><td>3 (14%)</td></tr><tr><td>Current occasional and regular smoker</td><td>44 (42,3%)</td><td>34 (41%)</td><td>10 (45%)</td></tr><tr><td>BMI (kg/m²) at inclusion: median</td><td>19.7</td><td>19.8</td><td>19.3</td></tr><tr><td>BMI < 18.5 kg/m² at inclusion</td><td>35 (34%)</td><td>26 (32%)</td><td>9 (45%)</td></tr><tr><td>Clinical presentation at inclusion</td><td></td><td></td><td></td></tr><tr><td>Cough</td><td>96 (94%)</td><td>75 (94%)</td><td>21 (95%)</td></tr><tr><td>Sputum (Productive cough)</td><td>91 (89%)</td><td>71 (89%)</td><td>20 (91%)</td></tr><tr><td>Dyspnea</td><td>53 (51%)</td><td>44 (54%)</td><td>9 (41%)</td></tr><tr><td>Temperature: median</td><td>37</td><td>37</td><td>37.2</td></tr><tr><td>Fever > 38°</td><td>31 (30.1%)</td><td>23 (28%)</td><td>8 (38.1%)</td></tr><tr><td>Abnormal chest X-ray at inclusion</td><td>100 (99%)</td><td>78 (99%)</td><td>22 (100%)</td></tr><tr><td>Bilateral infiltrates</td><td>48 (46%)</td><td>35 (45%)</td><td>13 (59%)</td></tr><tr><td>Cavity</td><td>70 (67%)</td><td>52 (66%)</td><td>18 (82%)</td></tr><tr><td>Miliary</td><td>3 (3%)</td><td>2 (3%)</td><td>1 (5%)</td></tr><tr><td>Extrathoracic location</td><td>7 (6.7%)</td><td>6 (7.3%)</td><td>1 (4.5%)</td></tr><tr><td>Pleural effusion</td><td>8 (8%)</td><td>6 (7.7%)</td><td>2 (9.1%)</td></tr><tr><td>Type of sample smear at inclusion</td><td></td><td></td><td></td></tr><tr><td>Sputum</td><td>97 (93%)</td><td>76 (93%)</td><td>21 (95%)</td></tr><tr><td>Bronchoaspiration or bronchoalveolar lavage or gastric aspirates</td><td>7 (7%)</td><td>6 (7%)</td><td>1 (5%)</td></tr><tr><td>Positive culture for Mycobacterium (complex) tuberculosis</td><td>102 (100%)</td><td>82 (100%)</td><td>20 (100%)</td></tr><tr><td>Drug susceptibility testing (phenotypic)</td><td></td><td></td><td></td></tr><tr><td>Rifampicin resistance</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Isoniazid resistance</td><td>6 (60%)</td><td>6 (75%)</td><td>0 (0%)</td></tr><tr><td>Ethambutol resistance</td><td>2 (20%)</td><td>2 (25%)</td><td>0 (0%)</td></tr><tr><td>Pyrazinamide resistance</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr></tbody></table>

Abbreviations: BMI: body mass index, C-M2: Negative culture at 2 months, C + M2: Positive culture at 2 months.

## 4. Discussion

The main finding of this prospective multicenter study of adult patients with smear-positive pulmonary TB is that the persistence of sputum and cough during treatment is associated with culture-positive sputum at M2. This is consistent with Hales et al. [25], who showed that productive cough was present in 51 % of patients with C + M2, compared to 29 % in those with C-M2 (P = 0.001). In that study, the initial analysis, adjusted for treatment duration, demonstrated that patients with cough were at two-fold higher risk of positive sputum culture. Therefore, in patients treated for pulmonary TB with persistent cough and/or sputum, monitoring of sputum culture at M2 is particularly important to determine whether, along with additional measures to ensure that treatment adherence is optimal, an additional three months of consolidation treatment may be necessary; it is also important to ensure that the risk of secondary transmission is controlled (e.g., no close contact with high-risk populations). Of note, there was a high proportion of active smokers in our cohort (42 %), which may have contributed to the high rate of patients with cough and sputum during follow-up, as smoking is a major cause of chronic bronchitis [26]. However, the percentage of smokers was identical in C + M2 and C-M2.

<caption>**Table 2**</caption>

Cough during treatment in the 104 patients with sputum culture at 2 months (M2). Cough was self-reported using a numerical scale ranging from 0 (no cough) to 4.

<table><thead><tr><th></th><th>Total (N = 104)</th><th>C-M2 (N = 82)</th><th>C + M2 (N = 22)</th><th>p-value</th></tr></thead><tbody><tr><td><strong>Cough at inclusion</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>6 (6%)</td><td>5 (6%)</td><td>1 (5%)</td><td rowspan="3">1</td></tr><tr><td>Yes</td><td>96 (94%)</td><td>75 (94%)</td><td>21 (95%)</td></tr><tr><td>Missing</td><td>2</td><td>2</td><td>0</td></tr><tr><td><strong>Cough at W2</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>16 (21%)</td><td>15 (22%)</td><td>1 (5%)</td><td rowspan="3">0.11</td></tr><tr><td>Yes</td><td>72 (79%)</td><td>53 (78%)</td><td>19 (95%)</td></tr><tr><td>Missing</td><td>16</td><td>14</td><td>2</td></tr><tr><td><strong>Cough at M1</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>25 (26%)</td><td>23 (30%)</td><td>2 (11%)</td><td rowspan="2">0.14</td></tr><tr><td>Yes</td><td>70 (74%)</td><td>53 (70%)</td><td>17 (89%)</td></tr><tr><td><strong>Missing</strong></td><td>9</td><td>6</td><td>3</td><td></td></tr><tr><td><strong>Cough at M2</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>50 (50%)</td><td>43 (54%)</td><td>7 (35%)</td><td rowspan="2">0.21</td></tr><tr><td>Yes</td><td>50 (50%)</td><td>37 (46%)</td><td>13 (65%)</td></tr><tr><td><strong>Missing</strong></td><td>4</td><td>2</td><td>2</td><td></td></tr><tr><td><strong>Cough at M4</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>55 (56%)</td><td>49 (64%)</td><td>6 (29%)</td><td rowspan="3">0.006</td></tr><tr><td>Yes</td><td>43 (44%)</td><td>28 (36%)</td><td>15 (71%)</td></tr><tr><td>Missing</td><td>6</td><td>5</td><td>1</td></tr><tr><td><strong>Cough at M6</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>64 (66%)</td><td>54 (71%)</td><td>10 (48%)</td><td rowspan="2">0.067</td></tr><tr><td>Yes</td><td>33 (34%)</td><td>22 (29%)</td><td>11 (52%)</td></tr><tr><td>Missing</td><td>7</td><td>6</td><td>1</td><td></td></tr></tbody></table>

Abbreviations: C-M2: Negative culture at 2 months, C + M2: Positive culture at 2 months.

<caption>**Table 3**</caption>

Sputum production during treatment in the 104 Patients with sputum culture at 2 months (M2). Sputum was self-reported using a numerical scale ranging from 0 (no sputum) to 4.

<table><thead><tr><th></th><th>Total (N = 104)</th><th>C-M2 (N = 82)</th><th>C + M2 (N = 22)</th><th>p-value</th></tr></thead><tbody><tr><td><strong>Sputum production at inclusion</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>11 (11%)</td><td>9 (11%)</td><td>2 (9%)</td><td rowspan="3">1</td></tr><tr><td>Yes</td><td>91 (89%)</td><td>71 (89%)</td><td>20 (91%)</td></tr><tr><td>Missing</td><td>2</td><td>2</td><td>0</td></tr><tr><td><strong>Sputum production at W2</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>31 (35%)</td><td>25 (37%)</td><td>6 (30%)</td><td rowspan="3">0.79</td></tr><tr><td>Yes</td><td>57 (65%)</td><td>43 (63%)</td><td>14 (70%)</td></tr><tr><td>Missing</td><td>16</td><td>14</td><td>2</td></tr><tr><td><strong>Sputum production at M1</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>41 (43%)</td><td>38 (50%)</td><td>3 (16%)</td><td rowspan="2">0.009</td></tr><tr><td>Yes</td><td>54 (57%)</td><td>38 (50%)</td><td>16 (84%)</td></tr><tr><td><strong>Missing</strong></td><td>9</td><td>6</td><td>3</td><td></td></tr><tr><td><strong>Sputum production at M2</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>57 (57%)</td><td>50 (63%)</td><td>7 (35%)</td><td rowspan="3">0.042</td></tr><tr><td>Yes</td><td>43 (43%)</td><td>30 (37%)</td><td>13 (65%)</td></tr><tr><td>Missing</td><td>4</td><td>2</td><td>2</td></tr><tr><td><strong>Sputum production at M4</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>76 (78%)</td><td>64 (83%)</td><td>12 (57%)</td><td rowspan="3">0.018</td></tr><tr><td>Yes</td><td>22 (22%)</td><td>13 (17%)</td><td>9 (43%)</td></tr><tr><td>Missing</td><td>6</td><td>5</td><td>1</td></tr><tr><td><strong>Sputum production at M6</strong></td><td></td><td></td><td></td><td>1</td></tr><tr><td>No</td><td>83 (86%)</td><td>65 (86%)</td><td>18 (86%)</td><td></td></tr><tr><td>Yes</td><td>14 (14%)</td><td>11 (14%)</td><td>3 (14%)</td><td></td></tr><tr><td>Missing</td><td>7</td><td>6</td><td>1</td><td></td></tr></tbody></table>

Abbreviations: C-M2: Negative culture at 2 months, C + M2: Positive culture at 2 months.
<table><caption>**Table 4**
Treatment outcomes in the 104 patients according to culture status at 2 months (M2).</caption><thead><tr><th></th><th>Total (N = 104)</th><th>C-M2 (N = 82)</th><th>C + M2 (N = 22)</th><th>p-value</th></tr></thead><tbody><tr><td>Treatment success</td><td>95 (91 %)</td><td>76 (93 %)</td><td>19 (86 %)</td><td>0.35</td></tr><tr><td>Bacteriological cure</td><td>65 (80 %)</td><td>56 (89 %)</td><td>9 (50 %)</td><td>&lt;0.001</td></tr><tr><td>Treatment failure</td><td></td><td></td><td></td><td></td></tr><tr><td>Death</td><td>2 (2 %)</td><td>1 (1 %)</td><td>1 (1 %)</td><td></td></tr><tr><td>Lost to follow-up</td><td>7 (7 %)</td><td>5 (6 %)</td><td>2 (9 %)</td><td></td></tr></tbody></table>

Abbreviations: C-M2: Negative culture at 2 months, C + M2: Positive culture at 2 months.

Other variables were numerically more common in C + M2 than in C-M2, including cavitary lesions (82 % vs 66 %) and bilateral lung involvement (59 % vs 45 %), but the differences were not statistically significant. According to Su et al. [11], 47 % of patients with C + M2 had baseline cavitary lesions, as compared to 20 % of patients with C-M2 (P < 0.001). Similarly, Hesseling et al. [19], reported that 64 % of patients with C + M2 had extensive lung involvement compared to 40 % of patients with C-M2 (OR = 2.71, 95 % CI 1.55–4.71, P = 0.001), and 93 % of patients with C + M2 had cavitary lesions as compared to 78 % with C-M2 (OR = 4.01, 95 % CI 1.74–9.20, P = 0.001).

The proportion of patients with a BMI < 18.5 kg/m² in our cohort was also numerically higher in the C + M2 group (45 vs 36 % in the C-M2). This finding is consistent with the literature [11]. Unfortunately, we did not collect quantitative data on weight loss at diagnosis, which could have been a more relevant factor than BMI insofar as it reflects recent changes related to the infection.

Out of the 177 participants in the FAST-TB study who attended M2 visits, 22/177 (12 %) were C + M2, a finding in line with the data of the literature. Prevalence of C + M2 ranged from 5 % to 30 % for Lee et al. [27], and amounted to 10 % for, Fitzwater et al. [28], and 21 % for Romanowski et al. [10]. Of note, patients enrolled in FAST-TB were all smear-positive, which is associated with advanced pulmonary TB by the time of diagnosis. In point of fact, culture positivity at M2 (C + M2) is correlated with bacillary load at diagnosis [11,13,16,17,19–21]. The overall treatment success rate in our study population was 91 % (95/104), with treatment failures observed in 7 % of the C-M2 group and 14 % of the C + M2 group (P = 0.349). However, most of these treatment failures were associated with loss to follow-up.

Duration of treatment did not differ significantly between the two groups. According to current recommendations, the C + M2 group should have received prolongation of the two-drug regimen (consolidation phase) for an additional three months. However, only half of the patients (11/22) with C + M2 extended their treatment beyond six months. Among the remaining 11 patients, nine had cavities and were therefore definitely eligible for this additional three-month treatment. Qin et al. [29] reported similar findings; in a cohort of over 5000 patients from the California TB Registry between 2004 and 2009, nearly a quarter of the patients (23 %) at risk of relapse, defined by the presence of cavitary lesions at diagnosis and C + M2, did not receive recommended additional treatment. These discrepancies between guidelines and practices suggest that physicians may not be aware of this recommendation for an additional three-month treatment in these particular situations.

Conversely, approximately a quarter of the patients with C-M2 received more than six months of treatment. This extension could not be explained by extra-thoracic locations, such as neuro-meningeal or osteo-articular TB. Additionally, the average duration of pyrazinamide treatment was 85 days, significantly longer than recommended [2,3].

Our study has limitations. First, due to limited sample size, it was not adequately powered to identify all of the factors associated with persistent positive culture at M2. This may help to explain why no baseline characteristics were associated with C + M2 status. Hence, our

study provides no robust data on the characteristics of patients who would benefit from prolonged induction therapy. The FAST-TB study had recruitment difficulties, due particularly to the national regulatory requirement that patients without baseline medical insurance coverage could not be enrolled in the study. Second, only 51 % of patients underwent sputum analysis at M2, which not only reduced our sample size, but could also introduced a selection bias. After all, the patients who underwent M2 sampling may have been more compliant with treatment constraints. TB treatment and follow-up adherence are fundamental for therapeutic success. Su et al. [11], demonstrated that patients under Directly Observed Therapy (DOT) had a higher rate of culture conversion at M2 compared to those with no DOT (OR 3.57, 95 % CI 1.94–6.55; P = 0.001). Nevertheless, the majority of patients in the FAST-TB study (177/203) attended follow-up consultations at M2, suggesting that the absence of sampling for M2 culture was primarily due to the resolution of cough and sputum. Patients with C + M2 were more likely to have sputum cultures performed at M4, in line with recommendations to monitor sputum cultures until conversion. However, due to the disappearance of their respiratory symptoms, approximately a quarter of patients with C + M2 had no sputum cultures performed at M4.

Comparison of patients who did not attend the M2 consultation with C-M2 patients highlights the importance of follow-up, and it is by no means surprising that the patients not evaluated at M2 had a higher rate of treatment failure.

In patients without sputum production, obtaining one or more induced sputum is a promising approach to assessing their bacteriological status. According to the meta-analysis by Luo et al. [30], the sensitivity and specificity of induced sputum for mycobacterial culture were 0.72 (95 % CI: 0.66–0.77) and 1.00 (95 % CI: 0.99–1.00), respectively, while bronchoscopy yielded sensitivity of 0.70 (95 % CI: 0.64–0.75) and specificity of 1.00 (95 % CI: 0.99–1.00). Given its diagnostic performance, induced sputum could be considered at M2 for non-expectorating patients. Its primary advantage lies in being non-invasive, although its use is limited by its short duration – approximately 30 min – and its poor tolerability.

Sputum culture at two months has its own limitations. Its performance is influenced by the (liquid or solid) culture media used. Historically, solid culture has been more commonly used, but liquid culture has better sensitivity [31,32]. Culture takes time (typically several weeks) and can be contaminated by fast-growing organisms. Additionally, a negative culture at two months may also result from a sub-optimal sputum sample. Last not but least, at two months some patients may no longer be able to produce sputum.

Although as a predictor of outcome culture conversion is the most validated biomarker, its performance remains modest. Positive cultures at M2 were associated with sensitivity of 40 % (95 % CI 25–56) and specificity of 85 % (95 % CI 77–91) to predict relapse [4], while another study [33] estimated their sensitivity at 33 % and their specificity at 71 % to predict treatment failure. Innovative biomarkers would help to improve our skills in prediction of outcome [34].

## 5. Conclusion

In conclusion, patients with smear-positive rifampicin-susceptible pulmonary TB with persistent cough and sputum on treatment are at increased risk of positive sputum cultures at M2. These simple clinical markers may be used as warning signs that pulmonary TB may be difficult to control and that the patients would be advised to consider prolonged anti-TB treatment.

### CRediT authorship contribution statement

Mickael Manchon: Conceptualization, Methodology, Writing – original draft. Mallorie Kerjouan: Conceptualization, Methodology, Writing – review & editing. Delphine Bachelet: Conceptualization, Methodology, Formal analysis. Stéphane Jouneau: Conceptualization,
Methodology, Writing – review & editing. **Charles Ricordel:** Conceptualization, Methodology. **Cédric Laouenan:** Conceptualization, Methodology. **Nathalie De Castro:** Conceptualization, Methodology, Writing – review & editing. **Pierre Tattevin:** Conceptualization, Methodology, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We wish to thank all the investigators and study staff involved in the
FAST-TB trial, as well as the patients who participated. We also
acknowledge the support of the French National Reference Center for
Mycobacteria and the clinical teams at participating centers.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.
org/10.1016/j.idnow.2025.105220.

References

[1] World Health Organization [Internet]. 2024. Global Tuberculosis Report 2024 [cited November 11, 2025]. Available from: https://www.who.int/teams/global-programme-on-tuberculosis-and-lung-health/tb-reports/global-tuberculosis-report-2024.

[2] Nahid P, Dorman SE, Alipanah N, Barry PM, Brozek JL, Cattamanchi A, et al. Official American Thoracic Society/Centers for Disease Control and Prevention/ Infectious Diseases Society of America Clinical Practice guidelines: Treatment of Drug-Susceptible Tuberculosis. Clin Infect Dis 2016;63(7):e147–95.

[3] Sotgiu G, Nahid P, Loddenkemper R, Abubakar I, Miravittles M, Migliori GB. The ERS-endorsed official ATS/CDC/IDSA clinical practice guidelines on treatment of drug-susceptible tuberculosis. Eur Respir J 2016;48(4):963–71.

[4] Horne DJ, Royce SE, Gooze L, Narita M, Hopewell PC, Nahid P, et al. Sputum monitoring during tuberculosis treatment for predicting outcome: systematic review and meta-analysis. Lancet Infect Dis 2010;10(6):387–94.

[5] Mitchison DA. Assessment of new sterilizing drugs for treating pulmonary tuberculosis by culture at 2 months. Am Rev Respir Dis 1993;147(4):1062-3.

[6] Benator D, Bhattacharya M, Bozeman L, Burman W, Cantazaro A, Chaisson R, et al. Rifapentine and isoniazid once a week versus rifampicin and isoniazid twice a week for treatment of drug-susceptible pulmonary tuberculosis in HIV-negative patients: a randomised clinical trial. Lancet Lond Engl 2002;360(9332):528–34.

[7] Perrin FM, Lipman MC, McHugh TD, Gillespie SH. Biomarkers of treatment response in clinical trials of novel antituberculosis agents. Lancet Infect Dis 2007;7(7):481–90.

[8] Jo KW, Yoo JW, Hong Y, Lee JS, Lee SD, Kim WS, et al. Risk factors for 1-year relapse of pulmonary tuberculosis treated with a 6-month daily regimen. Respir Med 2014;108(4):654–9.

[9] Phillips PPJ, Fielding K, Nunn AJ. An evaluation of culture results during treatment for tuberculosis as surrogate endpoints for treatment failure and relapse. PloS One 2013;8(5):e63840.

[10] Romanowski K, Balshaw RF, Benedetti A, Campbell JR, Menzies D, Ahmad Khan F, et al. Predicting tuberculosis relapse in patients treated with the standard 6-month regimen: an individual patient data meta-analysis. Thorax 2019;74(3):291–7.

[11] Su WJ, Feng JY, Chiu YC, Huang SF, Lee YC. Role of 2-month sputum smears in predicting culture conversion in pulmonary tuberculosis. Eur Respir J 2011;37(2): 376-83.

[12] Domínguez-Castellano A, Muniain MA, Rodríguez-Baño J, Garcia M, Rios MJ, Galvez J, et al. Factors associated with time to sputum smear conversion in active pulmonary tuberculosis. Int J Tuberc Lung Dis 2003;7(5):432–8.

[13] Singla R, Osman MM, Khan N, Al-Sharif N, Al-Sayegh MO, Shaikh MA. Factors predicting persistent sputum smear positivity among pulmonary tuberculosis patients 2 months after treatment. Int J Tuberc Lung Dis 2003;7(1):58-64.

[14] Hernandez-Romieu AC, Little BP, Bernheim A, Schechter MC, Ray SM, Bizune D, et al. Increasing Number and volume of Cavitary Lesions on Chest Computed Tomography are Associated with Prolonged Time to Culture Conversion in Pulmonary Tuberculosis. Open Forum. Infect Dis 2019;6(6):ofz232.

[15] Visser ME, Stead MC, Walzl G, Warren R, Schomaker M, Grewal HM, et al. Baseline predictors of sputum culture conversion in pulmonary tuberculosis: importance of cavities, smoking, time to detection and W-Beijing genotype. PloS One 2012;7(1): e29588.

[16] Mah A, Kharrat H, Ahmed R, Gao Z, Der E, Hansen E, et al. Serum drug concentrations of INH and RMP predict 2-month sputum culture results in tuberculosis patients. Int J Tuberc Lung Dis 2015;19(2):210–5.

[17] Telzak EE, Fazal BA, Pollard CL, Turett GS, Justman JE, Blum S. Factors influencing time to sputum conversion among patients with smear-positive pulmonary tuberculosis. Clin Infect Dis 1997;25(3):666-70.

[18] Güler M, Unsal E, Dursun B, Aydın O, Capan N. Factors influencing sputum smear and culture conversion time among patients with new case pulmonary tuberculosis. Int J Clin Pract 2007;61(2):231-5.

[19] Hesseling AC, Walzl G, Enarson DA, Carroll NM, Duncan K, Lukey PT, et al. Baseline sputum time to detection predicts month two culture conversion and relapse in non-HIV-infected patients. Int J Tuberc Lung Dis 2010;14(5):560-70.

[20] Velayutham BV, Allaudeen IS, Sivaramakrishnan GN, Perumal V, Nair D, Chinnaiyan P, et al. Sputum culture conversion with moxifloxacin-containing regimens in the treatment of patients with newly diagnosed sputum-positive pulmonary tuberculosis in South India. Clin Infect Dis 2014;59(10):e142-9.

[21] Kanda R, Nagao T, Tho NV, Ogawa E, Murakami Y, Osawa M, et al. Factors Affecting Time to Sputum Culture Conversion in adults with Pulmonary Tuberculosis: a Historical Cohort Study without Censored cases. PloS One 2015;10 (11):e0142607.

[22] Recomm Rep Morb Mortal Wkly Rep 2003;52(RR-11):1-77.

[23] De Castro N, Mechaï F, Bachelet D, Canestri A, Joly V, Vandenhende M, et al. Treatment with a Three-Drug Regimen for Pulmonary Tuberculosis based on Rapid Molecular Detection of Isoniazid Resistance: a Noninferiority Randomized Trial (FAST-TB). Open Forum. Infect Dis 2022;9(8):ofac353.

[24] Linh NN, Viny K, Gegia M, Falzon D, Glazious P, Floyd K, et al. World Health Organization treatment outcome definitions for tuberculosis: 2021 update. Eur Respir J 2021;58(2):2100804.

[25] Hales CM, Heilig CM, Chaisson R, Leung CC, Chang KC, Goldberg SV, et al. The association between symptoms and microbiologically defined response to tuberculosis treatment. Ann Am Thorac Soc 2013;10(1):18-25.

[26] Chung KF, Pavord ID. Prevalence, pathogenesis, and causes of chronic cough. Lancet Lond Engl 2008;371(9621):1364-74.

[27] Lee HY, Chae KO, Lee CH, Choi SM, Lee J, Park YS, et al. Culture Conversion Rate at 2 months of Treatment according to Diagnostic Methods among patients with Culture-positive Pulmonary Tuberculosis. PLoS ONE 2014;9(8):e103768.

[28] Fitzwater SP, Caviedes L, Gilman RH, Coronel J, LaChira D, Salazar C, et al. Prolonged infectiousness of tuberculosis patients in a directly observed therapy short-course program with standardized therapy. Clin Infect Dis 2010;51(4):371-8.

[29] Qin F, Barry PM, Pascopella L. Factors associated with extended treatment among tuberculosis patients at risk of relapse in California. Int J Tuberc Lung Dis 2016;20 (3):363-9.

[30] Luo W, Lin Y, Li Z, Wang W, Shi Y. Comparison of sputum induction and bronchoscopy in diagnosis of sputum smear-negative pulmonary tuberculosis: a systemic review and meta-analysis. BMC Pulm Med 2020;20(1):146.

[31] Phillips PPJ, Mendel CM, Nunn AJ, McHugh TD, Crook AM, Hunt R, et al. A comparison of liquid and solid culture for determining relapse and durable cure in phase III TB trials for new regimens. BMC Med 2017;15(1):207.

[32] Hongler J, Musaazi J, Ledergerber B, Eberhard N, Sekaggya-Wiltshire C, Keller PM, et al. Comparison of Löwenstein–Jensen and BACTEC MGIT 960 culture for Mycobacterium tuberculosis in people living with HIV. HIV Med 2018;19(9): 654-61.

[33] Magombedze G, Pasipanodya JG, Gumbo T. Bacterial load slopes represent biomarkers of tuberculosis therapy success, failure, and relapse. Commun Biol 2021;4(1):664.

[34] Goletti D, Lee MR, Wang JY, Walter N, Ottenhoff THM. Update on tuberculosis biomarkers: from correlates of risk, to correlates of active disease and of cure from disease. Respiriol Carlton Vic 2018;23(5):455-66.