Tuberculosis (TB) remains one of the most important infectious causes of morbidity and mortality worldwide. Drug-resistant TB adds substantial diagnostic and therapeutic complexity because delays in recognition permit ongoing transmission, inappropriate therapy, amplification of resistance, and poorer clinical outcomes. The World Health Organization (WHO) defines multidrug-resistant tuberculosis as disease caused by Mycobacterium tuberculosis complex resistant to at least both rifampicin and isoniazid. Rifampicin-resistant TB (RR-TB) and MDR-TB are commonly considered together programmatically as MDR/RR-TB.[1] Conventional phenotypic drug-susceptibility testing depends on isolation and growth of M. tuberculosis and may require several weeks before susceptibility results become available. Molecular diagnostic technologies have transformed this pathway. Xpert MTB/RIF and Xpert MTB/RIF Ultra simultaneously identify M. tuberculosis DNA and mutations within the rifampicin-resistance determining region of the rpoB gene. Line-probe assays such as GenoType MTBDRplus additionally assess mutations associated with rifampicin and isoniazid resistance, particularly within rpoB, katG, and the inhA promoter region.[2,3] An important diagnostic distinction is that an Xpert result indicating rifampicin resistance establishes RR-TB but does not, by itself, demonstrate MDR-TB because isoniazid susceptibility has not been determined. Confirmation or characterization of multidrug resistance therefore requires an assay capable of detecting isoniazid resistance or an appropriate phenotypic or sequencing-based drug-susceptibility test. In addition to resistance detection, several molecular assays provide indirect information regarding mycobacterial burden. Xpert MTB/RIF uses real-time polymerase chain reaction amplification, and the number of amplification cycles required for detectable fluorescence - the cycle-threshold (Ct) value - is inversely related to the amount of target DNA. Thus, lower Ct values generally indicate greater bacillary burden. Xpert and Xpert Ultra also categorize bacterial burden semiquantitatively as high, medium, low, very low, and, for Ultra, trace.[3]. Sputum smear microscopy remains an established indicator of pulmonary bacillary burden and infectious potential. Higher smear grades, especially 2+ and 3+, generally indicate greater concentrations of acid-fast bacilli. Chest radiography provides a complementary assessment of anatomical disease burden. Pulmonary cavitation, extensive parenchymal involvement, bilateral disease, fibrosis, bronchiectasis, and destructive lung changes have been frequently reported in patients with MDR-TB. None of these appearances, however, is pathognomonic for drug resistance. The relationship between molecular resistance detection, sputum bacillary burden, and structural pulmonary damage is clinically important. Patients with a high bacterial burden and extensive cavitary disease may constitute a particularly infectious and clinically severe phenotype in whom rapid resistance determination, respiratory isolation, and effective treatment are critical. The present systematic review therefore aimed to synthesize evidence concerning molecular detection of MDR/RR-TB and evaluate its relationship with sputum bacillary load and chest radiographic abnormalities. Objectives The primary objectives were to: (1) evaluate the performance and clinical utility of molecular methods for rapid detection of drug-resistant M. tuberculosis in pulmonary specimens; (2) examine the relationship between molecular bacterial-load indicators and conventional sputum smear bacillary load; (3) characterize chest radiographic and computed-tomographic abnormalities associated with MDR-TB; (4) examine whether bacillary burden correlates with the extent or severity of pulmonary radiographic abnormalities; and (5) determine the potential clinical value of integrating molecular, microbiological, and radiographic findings in patients with suspected MDR-TB.

Study Design and Reporting Framework This systematic review was designed according to the principles of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement.[4] Eligibility Criteria Studies were considered eligible when they included patients with bacteriologically confirmed pulmonary tuberculosis and evaluated MDR-TB, RR-TB, or other clinically significant drug-resistant pulmonary TB; assessed Xpert MTB/RIF, Xpert MTB/RIF Ultra, line-probe assays, PCR-based resistance assays, automated nucleic-acid amplification tests, or sequencing-based methods; reported sputum smear grade, molecular Ct values, semiquantitative molecular load, culture time-to-positivity, or other measures of bacillary burden; evaluated chest radiographic or computed-tomographic abnormalities; compared radiographic findings between drug-resistant and drug-sensitive TB; or analyzed relationships between bacteriological burden and radiographic extent. Studies restricted exclusively to extrapulmonary TB, non-human investigations, individual case reports, and reports without relevant molecular, sputum-load, or radiological outcomes were excluded. Information Sources and Search Strategy Electronic searches used combinations of disease-related terms (Mycobacterium tuberculosis, pulmonary tuberculosis, multidrug-resistant tuberculosis, MDR-TB, rifampicin-resistant tuberculosis, drug-resistant tuberculosis), molecular terms (Xpert MTB/RIF, GeneXpert, Xpert Ultra, line probe assay, GenoType MTBDRplus, PCR, nucleic acid amplification, molecular detection, drug-resistance mutation, targeted sequencing), bacillary-load terms (sputum smear, AFB smear grade, bacillary load, bacterial burden, cycle threshold, Ct value, semiquantitative, culture time to positivity), and radiological terms (chest radiograph, chest X-ray, CXR, cavitation, cavity, bilateral disease, disease extent, computed tomography, radiographic severity). Reference lists of relevant diagnostic-accuracy studies, systematic reviews, and WHO guidance documents were additionally screened. Study Selection The search identified 444 records: 426 through database searching and 18 through citation/reference searching. After removal of 108 duplicate records, 336 records underwent title and abstract screening, of which 252 were excluded. Eighty-four reports were sought for retrieval; four could not be retrieved, leaving 80 full-text reports for eligibility assessment. Sixty-two full-text reports were excluded because they did not specifically evaluate MDR/RR-TB (n = 18), lacked relevant molecular drug-resistance testing (n = 14), did not report sputum bacillary-load or relevant radiologic outcomes (n = 12), evaluated extrapulmonary TB or a non-relevant population (n = 7), were reviews/editorials/case reports or other non-primary research (n = 6), or represented duplicate study populations or had insufficient extractable data (n = 5). Eighteen primary studies were included in the qualitative synthesis (Figure 1). Data Extraction The following information was extracted where available: author and publication year; country or setting; study design and sample size; molecular diagnostic method; drug-resistance outcome; sputum smear grade; molecular Ct or semiquantitative load; culture-based bacillary-load measure; chest radiographic or CT abnormalities; measures of association between microbiological and radiological findings; and principal study conclusions. Quality Assessment Diagnostic-accuracy studies were interpreted using principles of QUADAS-2, including patient selection, index-test conduct, reference standard, and patient flow.[5] Observational imaging studies were evaluated according to cohort selection, comparability of resistant and susceptible groups, standardization of radiological interpretation, and adjustment for potential confounders such as previous treatment and HIV status. Data Synthesis A quantitative meta-analysis was not considered appropriate because of substantial clinical and methodological heterogeneity. Studies differed in molecular platform; definition of molecular bacterial burden; smear preparation and grading; use of solid versus liquid culture; definitions of MDR-, RR-, pre-XDR-, or XDR-TB; radiographic versus CT assessment; radiographic scoring systems; HIV prevalence; previous TB-treatment exposure; and sampling strategy. A structured qualitative synthesis was therefore undertaken.

Overview of Included Evidence The search yielded 444 records. After duplicate removal and title/abstract screening, 80 full-text reports were assessed for eligibility; 62 were excluded and 18 primary studies were included in the principal qualitative synthesis. Nine studies primarily addressed molecular diagnosis or molecular estimates of bacillary burden, seven principally evaluated radiographic patterns associated with drug-resistant tuberculosis, and two provided integrated assessments linking microbiological burden with radiographic disease severity. Table 1. Summary of evidence domains and principal findings Evidence domain Representative methods Consistent findings Clinical interpretation Rapid molecular resistance detection Xpert MTB/RIF, Xpert Ultra, MTBDRplus and other LPAs High diagnostic performance in smear-positive disease; reduced direct-test yield at low bacillary burden Molecular testing is essential for rapid resistance recognition; RIF resistance alone is not synonymous with MDR-TB Bacillary-load estimation AFB smear grade, Xpert/Ultra Ct, semiquantitative categories, culture time-to-positivity Lower Ct values correlate with higher smear grades and shorter culture time-to-positivity Molecular burden estimates complement smear microscopy but are not exact viable-bacillus counts Radiographic severity Chest radiography and CT MDR-TB cohorts show more cavitation, multiple/bilateral cavities, extensive involvement, bronchiectasis and destructive changes Imaging raises suspicion and defines structural severity but cannot establish resistance Integrated severity phenotype Molecular load + sputum burden + imaging extent High bacillary burden often coexists with extensive cavitary disease and worse outcomes in advanced drug-resistant TB Combined assessment may support isolation, monitoring and risk stratification Molecular Detection of Drug-Resistant Tuberculosis Boehme et al. demonstrated the diagnostic potential of Xpert MTB/RIF in a large multicountry study of patients with suspected drug-sensitive or multidrug-resistant pulmonary TB.[6] A single direct Xpert test identified approximately 98% of culture-confirmed smear-positive pulmonary TB cases, while sensitivity was lower among smear-negative culture-positive disease. This illustrates the interaction between molecular assay performance and bacillary burden. Xpert detects rifampicin resistance by interrogating the rpoB rifampicin-resistance determining region. Because rifampicin resistance frequently coexists with isoniazid resistance in high-burden settings, it provides an important warning for MDR-TB. Nevertheless, rifampicin resistance and MDR-TB should not be used interchangeably at the individual-patient level. Xpert MTB/RIF Ultra incorporates multicopy insertion-sequence targets in addition to rpoB, reducing its analytical detection threshold compared with the original Xpert assay.[3,13] Its increased sensitivity is particularly valuable in paucibacillary disease, although residual DNA in previously treated patients can complicate interpretation of very low-level positive results. Line-Probe Assays and Bacillary Burden Line-probe assays provide an advantage over rifampicin-only testing because MTBDRplus can identify mutations associated with both rifampicin and isoniazid resistance. Raizada et al. evaluated GenoType MTBDRplus directly on 320 smear-positive sputum specimens in India and reported high sensitivity and specificity for rifampicin resistance, with substantially shorter turnaround time than conventional culture-based susceptibility testing.[9] Ninan et al. similarly demonstrated strong performance of LPA for rifampicin and isoniazid resistance, but direct detection was better in smear-positive specimens than in smear-negative or scanty specimens.[11] In a large Central Indian programmatic experience, Desikan et al. tested 1,294 smear-positive specimens from MDR-TB suspects; among LPA-positive M. tuberculosis complex specimens, MDR, rifampicin monoresistance, and isoniazid monoresistance were all identified, demonstrating the utility of LPA for rapid programmatic stratification.[12] Taken together, these results indicate that low sputum bacterial burden does not exclude MDR-TB but may reduce the probability that a direct sputum line-probe assay will generate a fully interpretable resistance profile. Correlation Between Molecular Measurements and Sputum Bacillary Load One of the most consistent findings across the literature was the association between molecular Ct values and conventional bacillary-load measures. Blakemore et al. assessed 2,008 specimens from 741 patients and demonstrated that decreasing Xpert MTB/RIF Ct values were associated with increasing AFB smear grade, with inverse correlations of approximately -0.77 for concentrated sputum and -0.71 for direct sputum preparations.[7] Theron et al. likewise demonstrated that Ct values could provide useful information regarding sputum bacillary burden, although no single Ct cutoff reliably replaced smear microscopy for predicting smear status.[8] More recent Xpert Ultra evidence has confirmed meaningful correlations between Ct measurements, smear grade, and liquid-culture time-to-positivity.[14] Thus, a lower Ct value generally indicates a greater concentration of M. tuberculosis DNA and a higher sputum bacillary burden, whereas a higher Ct value is associated with paucibacillary disease. However, Ct should be interpreted as a semiquantitative molecular estimate rather than an exact measurement of viable bacilli. Sputum Bacillary Load and MDR-TB The relationship between bacillary load and resistance is clinically relevant but should not be interpreted as causal. MDR-TB does not inherently require a high bacillary burden, and paucibacillary disease may still contain highly resistant organisms. Nevertheless, multiple observational studies have reported higher smear positivity and greater smear grades among established MDR-TB populations, potentially reflecting delayed effective therapy, previous treatment failure, prolonged disease duration, and extensive cavitary pathology. Chuchottaworn et al. provided particularly informative evidence: an AFB smear grade of 3+ was independently associated with MDR-TB, with an odds ratio of approximately 13.09, while cavitation and previous treatment-related factors were also associated with resistance.[19] A 3+ smear is not diagnostic of MDR-TB, but in an appropriate epidemiological context it should increase the urgency of rapid molecular drug-susceptibility testing. Chest Radiographic Findings in MDR-TB Cavitation emerged as the most consistently reported radiological feature associated with MDR-TB. Kim et al. found cavitation to be significantly more frequent in MDR-TB than in matched drug-sensitive TB, and multiple cavities were particularly characteristic of the resistant cohort.[15] Yeom et al. similarly reported that bilateral involvement and increasing cavity number were independently associated with primary MDR-TB.[17] Chuchottaworn et al. reported substantially more cavitation among MDR-TB patients than drug-sensitive controls; large cavities, three or more cavities, bilateral cavitation, and involvement of multiple lung zones occurred more often in MDR-TB.[19] Icksan et al. also observed much greater lesion extent, cavitation, fibrosis, bronchiectasis, and destructive changes among MDR-TB patients.[21] These findings suggest that cavity number, distribution, and size may carry more discriminatory information than the simple presence or absence of a cavity. Nevertheless, bilateral or cavitary disease remains nonspecific and also occurs in advanced drug-sensitive TB. Relationship Between Bacillary Load and Radiographic Severity The association between cavity formation and bacillary burden has a strong biological basis. Cavities contain large extracellular populations of M. tuberculosis and communicate with the airways, facilitating sputum bacillary shedding and transmission. te Riele et al. evaluated patients with extensively drug-resistant TB and found that cavitation, disease extent, and overall radiographic severity correlated with microbiological bacterial burden measured by culture time-to-positivity. Greater radiographic severity was also associated with poorer treatment outcomes.[22] This supports a clinically relevant pathway in which greater pulmonary destruction can coexist with higher bacillary burden and adverse outcome risk. Recent evidence evaluating combined molecular bacterial burden and chest-radiographic disease extent further supports the concept that these domains provide complementary prognostic information, even though such evidence is not specific to MDR-TB alone.[23] Integrated Interpretation of Molecular, Sputum and Radiographic Findings The overall evidence supports a three-component framework: molecular testing establishes the resistance profile; sputum smear, Ct value, semiquantitative molecular category, and culture time-to-positivity estimate bacillary burden; and chest radiography or CT defines anatomical disease burden. No component should replace the others. A patient may have MDR-TB with low bacillary burden and minimal radiographic disease, particularly when detected early. Conversely, extensive cavitation and a 3+ smear may occur in severe drug-sensitive TB. Molecular drug-susceptibility testing therefore remains essential. Table 2. Detailed characteristics of the primary studies included in the qualitative synthesis Study Setting / design Sample Index / assessment Bacillary-load measure Radiographic component Principal finding Boehme et al., 2010[6] Multicountry prospective diagnostic study 1,730 evaluable participants Xpert MTB/RIF vs culture/DST Smear status; molecular detection level No primary imaging comparison Very high sensitivity in smear-positive TB; lower sensitivity in smear-negative disease; rapid RIF-resistance detection. Blakemore et al., 2011[7] Multisite quantitative Xpert assessment 741 patients; 2,008 specimens Xpert MTB/RIF Ct, smear grade, CFU/culture measures None Ct inversely correlated with smear grade (about -0.71 to -0.77); supported Ct as semiquantitative burden marker. Theron et al., 2012[8] Pulmonary TB cohort Study cohort of Xpert-positive pulmonary specimens Xpert MTB/RIF Ct vs smear status None Ct predicted smear positivity reasonably well but no universal cutoff could fully replace smear microscopy. Raizada et al., 2014[9] India; multisite validation 320 smear-positive sputum specimens GenoType MTBDRplus Smear-positive direct specimens None High sensitivity/specificity for RIF resistance; rapid direct MDR-related testing compared with conventional DST. Madhuri et al., 2015[10] India; diagnostic utility study 100 AFB-positive specimens Line probe assay AFB smear grades including 2+ and 3+ None Demonstrated rapid detection of RIF/INH resistance in smear-positive pulmonary samples. Ninan et al., 2016[11] South India; MDR-TB suspects 91 patients Line probe assay Smear-positive, scanty, smear-negative categories None Strong resistance detection in smear-positive disease; lower direct-test performance at low bacillary burden. Desikan et al., 2017[12] Central India; programmatic study 1,294 smear-positive specimens Line probe assay Smear-positive specimens None Among LPA-positive MTB specimens, MDR and mono-resistance patterns were rapidly identified, supporting programmatic use. Dorman et al., 2018[13] Multicentre prospective diagnostic study 1,439 participants in primary diagnostic analysis Xpert MTB/RIF Ultra vs Xpert/culture Smear status; semiquantitative molecular detection None Ultra increased sensitivity, particularly in paucibacillary disease, with high RIF-resistance detection performance. Martin-Higuera et al., 2023[14] Pulmonary TB laboratory cohort 204 Xpert Ultra-positive specimens Xpert MTB/RIF Ultra Ct, smear grade, liquid-culture TTP None Strong relationship between Ultra Ct and smear/culture burden; Ct useful for rapid burden estimation. Kim et al., 2004[15] HIV-negative MDR vs drug-sensitive TB 47 MDR-TB + 47 matched DS-TB Drug-susceptibility classification Not primary endpoint Chest CT MDR-TB showed more cavitation; multiple cavities were particularly suggestive of resistant disease. Cha et al., 2009[16] DS-, MDR-, and XDR-TB comparison Comparative radiologic cohorts Resistance category by DST Not primary endpoint CXR and CT Multiple cavities and bronchial dilatation were more frequent with increasing drug resistance. Yeom et al., 2009[17] Primary MDR vs drug-sensitive TB Comparative cohort Primary MDR status Not primary endpoint Chest CT Bilateral disease and increasing cavity number independently associated with primary MDR-TB. Dholakia et al., 2012[18] Mumbai TB programme Programmatic pulmonary TB cohort DST-based resistance classification Smear/culture information in programme data Chest radiography Bilateral cavitation and extensive abnormalities were associated with MDR phenotype. Chuchottaworn et al., 2015[19] Thailand; case-control study 145 MDR-TB + 145 DS-TB DST-defined MDR-TB AFB smear grade Chest radiography AFB 3+ and cavitation independently associated with MDR-TB; large, multiple, bilateral cavities were more frequent. Li et al., 2017[20] HIV-negative primary MDR vs DS-TB 89 MDR-TB + 89 DS-TB DST-defined primary MDR-TB Not primary endpoint Chest CT Greater extent of cavitary lesions and bronchiectasis in primary MDR-TB. Icksan et al., 2018[21] MDR vs drug-sensitive TB 183 MDR-TB + 183 DS-TB Resistance category Not primary endpoint Chest radiography MDR-TB associated with much greater lesion extent, cavitation, fibrosis, bronchiectasis and destructive changes. te Riele et al., 2019[22] South Africa; XDR-TB cohort 97 patients XDR-TB classification Culture time-to-positivity Chest radiographic severity score Radiographic cavitation and extent correlated with bacterial burden and were associated with adverse outcomes. Grint et al., 2026[23] RIFASHORT cohort secondary analysis Trial cohort; pulmonary TB Xpert/Ultra burden measures Semiquantitative molecular burden / Ct Chest radiographic extent Combined high molecular burden and extensive CXR disease identified a clinically severe, higher-risk phenotype; not MDR-specific. Abbreviations: AFB, acid-fast bacilli; CFU, colony-forming units; CXR, chest radiograph; Ct, cycle threshold; DS-TB, drug-sensitive tuberculosis; DST, drug-susceptibility testing; INH, isoniazid; LPA, line-probe assay; MDR-TB, multidrug-resistant tuberculosis; RIF, rifampicin; TTP, time-to-positivity; XDR-TB, extensively drug-resistant tuberculosis.

This systematic review demonstrates that rapid molecular diagnostics, sputum bacillary-load measurements, and chest imaging represent complementary rather than competing approaches to evaluation of drug-resistant pulmonary tuberculosis. The first major finding was the high diagnostic value of molecular assays. Xpert MTB/RIF markedly shortened the time required to recognize rifampicin-resistant TB, while line-probe assays extended rapid resistance detection to isoniazid. More recent molecular platforms and sequencing approaches broaden the number of drugs for which resistance can be characterized. The critical interpretive distinction remains that rifampicin resistance detected by Xpert should trigger management for RR-TB and additional testing, but it does not itself establish resistance to isoniazid. The second major finding was the strong relationship between molecular bacterial burden and sputum microscopy. Xpert Ct values consistently showed an inverse relationship with smear grade: specimens containing larger concentrations of M. tuberculosis DNA required fewer amplification cycles to cross the detection threshold. However, Ct measurements should not be interpreted as exact quantitative cultures because DNA amplification may detect both viable and nonviable organisms and is influenced by specimen quality, inhibition, processing, and assay platform. The third important finding was that direct molecular resistance testing becomes less consistently interpretable at very low bacillary loads. This issue is especially relevant to line-probe assays. High performance demonstrated in smear-positive samples cannot be extrapolated without qualification to smear-negative disease, where culture followed by molecular or phenotypic testing may still be required. The fourth major finding was a consistent association between MDR-TB and cavitary or extensive pulmonary abnormalities. Multiple studies across different geographic settings reported greater cavitation, multiple cavities, bilateral disease, bronchiectasis, fibrosis, and overall disease extent among MDR-TB patients compared with drug-sensitive controls. Nevertheless, previous unsuccessful treatment and longer disease duration can confound this relationship. Studies of primary MDR-TB still suggest that cavity number and bilateral involvement can be associated with resistance, indicating that chronicity alone does not fully explain the pattern. The fifth finding concerned the relationship between radiographic severity and bacterial burden. Cavitary lesions provide a biological environment in which large extracellular populations of bacilli can accumulate and drain into the conducting airways, explaining the frequent association between cavitation, smear positivity, and transmissibility. In advanced drug-resistant TB, radiographic extent and cavitation have been directly correlated with culture-based bacterial burden and adverse treatment outcomes.[22] The integrated model proposed in Figure 2 therefore has practical value: molecular testing answers whether resistance-associated mutations are present; microbiological burden measurements estimate the quantity of organisms being shed; and imaging defines the anatomical consequences of disease. A patient with confirmed resistance, a high smear or low Ct value, and extensive bilateral cavitation represents a different infection-control and clinical-risk phenotype from a patient with early, low-burden, minimally destructive disease, even though both may have MDR-TB. Implications for Clinical Practice Patients with pulmonary TB should be prioritized for rapid comprehensive resistance testing when one or more high-risk features coexist, particularly previous treatment or treatment failure, known MDR/RR-TB exposure, persistent smear positivity, AFB smear grade 3+, high or medium molecular bacillary load, low Xpert Ct value, large pulmonary cavities, three or more cavities, bilateral cavitary disease, extensive multizonal involvement, or progressive radiographic abnormalities despite therapy. These variables identify risk and disease burden; they do not independently establish resistance. Implications for Infection Control The combination of low Ct, high smear grade, and extensive cavitary disease is consistent with a large respiratory bacillary burden and may indicate increased infectiousness. Rapid recognition may support timely airborne precautions, contact investigation, rapid initiation of an effective drug-resistant TB regimen, prioritization of repeat sputum testing, and close monitoring of microbiological conversion. Conversely, smear negativity must not be interpreted as absence of drug-resistant TB because sensitive molecular assays and culture can detect disease at much lower organism concentrations. Role of Chest CT Most TB programmes rely principally on chest radiography because of its availability, lower cost, and lower radiation exposure. CT provides superior characterization of small cavities, cavity wall morphology, tree-in-bud nodules, bronchiectasis, endobronchial spread, subtle bilateral disease, destroyed lung, and mediastinal abnormalities. CT is not routinely required to diagnose MDR-TB but can be useful when chest radiography underestimates disease extent or complications and structural detail may influence management. Strengths of the Review This review integrates three areas that are frequently studied independently: molecular resistance detection, sputum bacillary burden, and pulmonary imaging. Additional strengths include the distinction between RR-TB and confirmed MDR-TB; evaluation of bacillary-load effects on molecular assay performance; inclusion of both chest radiography and CT evidence; and emphasis on clinically meaningful integration rather than reliance on a single test. Limitations Substantial heterogeneity prevented a meaningful pooled meta-analysis. Bacillary burden was measured using smear grade, Ct values, semiquantitative molecular categories, or culture time-to-positivity, while radiographic severity was evaluated using different methods and scoring systems. Many radiological investigations were retrospective and therefore potentially vulnerable to selection and information bias. Previous TB treatment was more common among MDR-TB patients in several cohorts, and some extensive radiographic abnormalities may therefore reflect chronicity or previous ineffective therapy rather than resistance itself. HIV infection can modify both radiographic presentation and sputum bacillary burden, potentially weakening associations between cavitation, smear positivity, and resistance. Evidence directly evaluating molecular resistance, molecular bacterial burden, and standardized radiographic severity simultaneously within the same MDR-TB cohort remains limited. A universal molecular Ct threshold defining infectiousness, radiographic severity, or MDR-TB cannot currently be recommended because Ct values depend on assay type, specimen processing, PCR inhibition, and patient characteristics. Study selection was documented using a PRISMA 2020 flow diagram, with 444 records identified and 18 primary studies ultimately included. Nevertheless, the breadth of study designs, diagnostic platforms, bacillary-load measures, and radiographic scoring systems limited direct comparability across studies. Future Research Future prospective studies should evaluate molecular, microbiological, and radiographic characteristics concurrently at the time of diagnosis and use a standardized dataset including Xpert/Ultra Ct or semiquantitative category, comprehensive resistance profile, AFB smear grade, liquid-culture time-to-positivity, standardized chest-radiographic severity score, cavity number and size, HIV status, previous TB treatment, time to smear and culture conversion, recurrence, and mortality. Quantitative imaging and machine-learning approaches integrating molecular bacterial burden with chest radiography may eventually improve risk stratification, but such tools should augment rather than replace microbiological drug-susceptibility testing.

Molecular diagnostic assays have fundamentally improved recognition of drug-resistant pulmonary tuberculosis by reducing diagnostic delay from weeks to hours or days. Xpert MTB/RIF and Xpert MTB/RIF Ultra provide rapid detection of M. tuberculosis and rifampicin resistance, while line-probe assays and additional molecular approaches allow broader characterization of drug resistance. Sputum bacillary burden substantially influences molecular diagnostic performance. Lower Xpert Ct values are consistently associated with higher sputum smear grades and greater culture-based bacterial burden, whereas paucibacillary disease increases the likelihood of smear negativity and may decrease interpretability of direct line-probe testing. MDR-TB is more frequently associated with extensive pulmonary abnormalities, particularly cavitation, multiple cavities, bilateral disease, bronchiectasis, and greater overall radiographic involvement. Nevertheless, neither bacillary load nor chest radiographic appearance can independently diagnose MDR-TB. Multiple or bilateral cavities should prompt rapid resistance testing rather than empirical classification as MDR-TB. The most clinically informative approach is therefore an integrated one in which molecular testing establishes resistance, sputum measurements estimate bacillary burden, and chest imaging defines anatomical disease severity. Combining these complementary domains may permit earlier identification of patients with highly resistant and high-burden pulmonary disease, improve infection-control decisions, and support individualized monitoring and management. Declarations Ethics Approval: Ethical approval was not required because this study was a systematic review of previously published data and did not involve recruitment of human participants or collection of identifiable patient information. Consent for Publication: Not applicable. Availability of Data and Materials: All data summarized in this review were derived from publicly available published literature. Competing Interests: The authors declare no competing interests. Funding: No specific funding was received for this systematic review. Author Contributions: Siddhant Ray: conceptualization, literature review, data synthesis, manuscript drafting. S. Zeeshan Ahmad Hashmi: methodology, microbiological interpretation, critical review. Manish Jha: radiological interpretation, imaging evidence synthesis, critical review. All authors reviewed and approved the final manuscript..

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