Accuracy of Tongue Swab Testing Using Xpert MTB-RIF Ultra for Tuberculosis Diagnosis.

Tongue dorsum swabs have shown promise as alternatives to sputum for detecting Mycobacterium tuberculosis (MTB) in patients with pulmonary tuberculosis (TB). Some of the most encouraging results have come from studies that used manual quantitative PCR (qPCR) to analyze swabs. Studies using the automated Cepheid Xpert MTB/RIF Ultra qPCR test (Xpert Ultra) have exhibited less sensitivity with tongue swabs, possibly because Xpert Ultra is optimized for testing sputum, not tongue swab samples. Using two new sample preprocessing methods that demonstrated good sensitivity in preliminary experiments, we assessed diagnostic accuracy and semi-quantitative signals of Xpert Ultra performed on tongue swabs collected from 183 adults with presumed TB in Kampala, Uganda. Relative to a sputum Xpert Ultra reference standard, the sensitivity of tongue swab Xpert Ultra was 77.8% (95% confidence interval [CI] 64.4-88.0) and specificity was 100.0% (95% CI, 97.2-100.0). When compared to a microbiological reference standard (MRS) incorporating both sputum Xpert Ultra and sputum mycobacterial culture, sensitivity was 72.4% (95% CI, 59.1-83.3) and specificity remained the same. Semi-quantitative Xpert Ultra results were generally lower with tongue swabs than with sputum, and cycle threshold values were higher. None of the eight sputum Xpert Ultra "trace" or "very low" results were detected using tongue swabs. Tongue swabs should be considered when sputum cannot be collected for Xpert Ultra testing, or in certain mass-screening settings. Further optimization of tongue swab analysis is needed to achieve parity with sputum-based molecular testing for TB.

Impact of heteroresistance on treatment outcomes of people with drug-resistant TB.

BACKGROUND: Poor treatment outcomes among people with drug-resistant TB (DR-TB) are a major concern. Heteroresistance (presence of susceptible and resistant Mycobacterium tuberculosis in the same sample) has been identified in some people with TB, but its impact on treatment outcomes is unknown. METHODS: We used targeted deep sequencing to identify mutations associated with DR-TB and heteroresistance in culture samples of 624 people with DR-TB. We evaluated the association between heteroresistance and time to unfavorable treatment outcome using Cox proportional hazards regression. RESULTS: The proportion of drug-resistant isolates with a known mutation conferring resistance was lower for streptomycin (45.2%) and second-line injectables (79.1%) than for fluoroquinolones (86.7%), isoniazid (93.2%) and rifampin (96.5%). Fifty-two (8.3%) had heteroresistance, and it was more common for fluoroquinolones (4.6%) than rifampin (2.2%), second-line injectables (1.4%), streptomycin (1.7%), or isoniazid (1.3%). There was no association between heteroresistance and time to unfavorable outcome among people with multidrug-resistant TB (adjusted hazard ratio [aHR] 1.74, 95% CI 0.39-7.72) or pre-extensively DR-TB (aHR 0.65, 95% CI 0.24-1.72). CONCLUSIONS: Heteroresistance was relatively common (8.3%) among people with DR-TB in the Philippines. However, we found insufficient evidence to demonstrate an impact on unfavorable treatment outcomes.

CONTEXTE: Les résultats médiocres du traitement chez les personnes atteintes de TB résistante aux médicaments (DR-TB, pour l'anglais « drug-resistant TB ¼) constituent une préoccupation significative. L'hétérorésistance, caractérisée par la coexistence de souches sensibles et résistantes de Mycobacterium tuberculosis dans un même échantillon, a été observée chez certains patients, mais les conséquences de cette situation sur l'efficacité des traitements demeurent incertaines. MÉTHODES: Nous avons recouru au séquençage profond ciblé afin d'identifier les mutations liées à la DR-TB et à l'hétérorésistance dans les échantillons de culture provenant de 624 personnes atteintes de DR-TB. Nous avons analysé le lien entre l'hétérorésistance et le délai jusqu'à l'issue défavorable du traitement en utilisant une régression des risques proportionnels de Cox. RÉSULTATS: La proportion d'isolats, présentant une mutation connue associée à la résistance, était inférieure pour la streptomycine (45,2%) et les médicaments injectables de deuxième ligne (79,1%) par rapport aux fluoroquinolones (86,7%), à l'isoniazide (93,2%) et à la rifampicine (96,5%). Parmi les isolats, cinquante-deux (8,3%) manifestaient une hétérorésistance, plus courante pour les fluoroquinolones (4,6%) que pour la rifampicine (2,2%), les médicaments injectables de deuxième ligne (1,4%), la streptomycine (1,7%) ou l'isoniazide (1,3%). Aucune association n'a été observée entre l'hétérorésistance et un délai d'évolution défavorable chez les patients atteints de TB multirésistante (rapport de risque ajusté [aHR] 1,74 ; IC à 95% 0,39­7,72) ou de DR-TB pré-extensive (aHR 0,65 ; IC à 95% 0,24­1,72). CONCLUSIONS: L'hétérorésistance a été observée de manière relativement fréquente (8,3%) chez les personnes atteintes de DR-TB aux Philippines. Néanmoins, nous n'avons pas identifié de preuves suffisantes pour établir un lien avec des résultats de traitement défavorables.

Magnitude of Mycobacterium tuberculosis transmission among household and non-household contacts of TB patients.

The household and non-household contacts of patients with tuberculosis (TB) face varying degrees of risk of infection by Mycobacterium tuberculosis. To quantify new infection and to determine the risk factors associated with new infection among named contacts in San Francisco, CA, USA. We performed a cohort study in patients with culture-positive pulmonary TB. We analyzed patient, contact, environmental and bacterial characteristics. Of the 2422 contacts named by 256 patients, 149 (6.2%) had new infection due to recent transmission from 79 (30.9%) patients. Of the 149 new infections, 87 (58.4%) occurred among household contacts and 62 (41.6%) among non-household contacts. Numerous acid-fast bacilli in sputum (odds ratio [OR] 2.64, 95%CI 1.32-5.25) and contacts being named by more than one patient (OR 2.90, 95%CI 1.23-6.85) were associated with new infection among household contacts. Being older than 50 years (OR 1.93, 95%CI 1.09-3.41) and an Asian/Pacific Islander (OR 3.09, 95%CI 1.50-6.37) were associated with new infection among non-household contacts. Fewer than one third of patients caused new infection to his/her contacts. A substantial proportion of transmission resulting in new infection occurred outside of the household. The risk factors for infection among household and non-household contacts are different and should be considered when prioritizing control interventions. .

Interplay of strain and race/ethnicity in the innate immune response to M. tuberculosis.

BACKGROUND: The roles of host and pathogen factors in determining innate immune responses to M. tuberculosis are not fully understood. In this study, we examined host macrophage immune responses of 3 race/ethnic groups to 3 genetically and geographically diverse M. tuberculosis lineages. METHODS: Monocyte-derived macrophages from healthy Filipinos, Chinese and non-Hispanic White study participants (approximately 45 individuals/group) were challenged with M. tuberculosis whole cell lysates of clinical strains Beijing HN878 (lineage 2), Manila T31 (lineage 1), CDC1551 (lineage 4), the reference strain H37Rv (lineage 4), as well as with Toll-like receptor 2 agonist lipoteichoic acid (TLR2/LTA) and TLR4 agonist lipopolysaccharide (TLR4/LPS). Following overnight incubation, multiplex assays for nine cytokines: IL-1ß, IL-2, IL-6, IL-8, IL-10, IL-12p70, IFNγ, TNFα, and GM-CSF, were batch applied to supernatants. RESULTS: Filipino macrophages produced less IL-1, IL-6, and more IL-8, compared to macrophages from Chinese and Whites. Race/ethnicity had only subtle effects or no impact on the levels of IL-10, IL-12p70, TNFα and GM-CSF. In response to the Toll-like receptor 2 agonist lipoteichoic acid (TLR2/LTA), Filipino macrophages again had lower IL-1 and IL-6 responses and a higher IL-8 response, compared to Chinese and Whites. The TLR2/LTA-stimulated Filipino macrophages also produced lower amounts of IL-10, TNFα and GM-CSF. Race/ethnicity had no impact on IL-12p70 levels released in response to TLR2/LTA. The responses to TLR4 agonist lipopolysaccharide (TLR4/LPS) were similar to the TLR2/LTA responses, for IL-1, IL-6, IL-8, and IL-10. However, TLR4/LPS triggered the release of less IL-12p70 from Filipino macrophages, and less TNFα from White macrophages. CONCLUSIONS: Both host race/ethnicity and pathogen strain influence the innate immune response. Such variation may have implications for the development of new tools across TB therapeutics, immunodiagnostics and vaccines.

Impact of Euro-American sublineages of Mycobacterium tuberculosis on new infections among named contacts.

BACKGROUND: The impact of demographic, clinical, and bacterial factors on new infection by Euro-American lineage Mycobacterium tuberculosis among contacts of patients with tuberculosis (TB) has not been evaluated. OBJECTIVE: To describe the risk factors for new infection by Euro-American M. tuberculosis sublineages in San Francisco, California. DESIGN: We included contacts of patients with TB due to Euro-American M. tuberculosis. Sublineages were determined by large-sequence polymorphisms. We used tuberculin skin testing or QuantiFERON®-TB Gold In-Tube to identify contacts with new infection. Regression models with generalized estimating equations were used to determine the risk factors for new infection. RESULTS: We included 1488 contacts from 134 patients with TB. There were 79 (5.3%) contacts with new infection. In adjusted analyses, contacts of patients with TB due to region of difference 219 M. tuberculosis sublineage were less likely to have new infection (OR 0.23, 95%CI 0.06-0.84) than those with other sublineages. Other risk factors for new infection were contacts exposed to more than one patient with TB, contacts exposed for 30 days, or contacts with a history of smoking or excessive alcohol consumption. CONCLUSIONS: In addition to well-known exposure and clinical characteristics, bacterial characteristics independently contribute to the transmissibility of TB in San Francisco.

Clinical and bacteriological characteristics associated with clustering of multidrug-resistant tuberculosis.

SETTING: The impact of the genetic characteristics of Mycobacterium tuberculosis on the clustering of multidrug-resistant tuberculosis (MDR-TB) has not been analyzed together with clinical and demographic characteristics. OBJECTIVE: To determine factors associated with genotypic clustering of MDR-TB in a community-based study. DESIGN: We measured the proportion of clustered cases among MDR-TB patients and determined the impact of clinical and demographic characteristics and that of three M. tuberculosis genetic characteristics: lineage, drug resistance-associated mutations, and rpoA and rpoC compensatory mutations. RESULTS: Of 174 patients from California and Texas included in the study, the number infected by East-Asian, Euro-American, Indo-Oceanic and East-African-Indian M. tuberculosis lineages were respectively 70 (40.2%), 69 (39.7%), 33 (19.0%) and 2 (1.1%). The most common mutations associated with isoniazid and rifampin resistance were respectively katG S315T and rpoB S531L. Potential compensatory mutations in rpoA and rpoC were found in 35 isolates (20.1%). Hispanic ethnicity (OR 26.50, 95%CI 3.73-386.80), infection with an East-Asian M. tuberculosis lineage (OR 30.00, 95%CI 4.20-462.40) and rpoB mutation S531L (OR 4.03, 95%CI 1.05-23.10) were independent factors associated with genotypic clustering. CONCLUSION: Among the bacterial factors studied, East-Asian lineage and rpoB S531L mutation were independently associated with genotypic clustering, suggesting that bacterial factors have an impact on the ability of M. tuberculosis to cause secondary cases.

Reduced sensitivity of the QuantiFERON(®) test in diabetic patients with smear-negative tuberculosis.

SETTING: Immunosuppressive conditions have been associated with low sensitivity of interferon-gamma release assays (IGRAs) and the tuberculin skin test (TST) for the diagnosis of tuberculosis (TB). However, no systematic analysis of patient and bacterial characteristics has been performed before. OBJECTIVE: To determine the sensitivity and the risk factors for false-negative QuantiFERON(®)-TB (QFT) assay and TST in TB patients. DESIGN: We performed a retrospective analysis of data collected in a community-based study of TB in San Francisco, CA, USA. We included 300 TB patients who underwent QFT and TST. RESULTS: The risk factors for false-negative QFT were human immunodeficiency virus infection and the use of QuantiFERON(®)-TB Gold. In patients with sputum smear-negative TB, diabetes mellitus (DM) was associated with false-negative QFT (OR 2.85, 95%CI 1.02-7.97, P = 0.045). TST sensitivity was higher than QFT sensitivity in DM patients (OR 9.46, 95%CI 2.53-35.3). CONCLUSIONS: In San Francisco, QFT sensitivity was lower than that of TST, especially in patients with DM. Stratified analysis by sputum smear results showed that this association was specific to smear-negative TB. In contrast, TST was not affected by the presence of DM.

Serum biomarkers of treatment response within a randomized clinical trial for pulmonary tuberculosis.

RATIONALE: Biomarkers for monitoring response to anti-tuberculosis treatment are needed. We explored immune markers previously published as having predictive capability for 8 week culture status in 39 adults enrolled in a clinical trial in Kampala, Uganda. METHODS: We consecutively selected 20 HIV-negative pulmonary TB subjects with positive cultures, and 19 subjects with negative cultures at the end of intensive phase therapy. At baseline and after 8 weeks, serum was assayed for nine cytokines and soluble cytokine receptors using multiplexed platforms or ELISA. We evaluated their association with week 8 culture status first using single-variable logistic models, then using cross-validated estimates of the C-statistic, a measure of discrimination, of candidate models including 2 or 3 analytes in addition to age. RESULTS: All but one analyte decreased from baseline to week 8 (all p < 0.01). Individual biomarkers were not associated with 8 week culture status. Logistic models including increasing age, higher baseline soluble tumor necrosis factor receptor alpha 1 (sTNF-R1), and higher week 8 C-reactive protein (CRP) concentration classified subjects by culture status with up to 85% accuracy and acceptable discrimination (cross-validated C-statistic 0.76) and calibration (Hosmer-Lemeshow P > 0.2). CONCLUSION: Exploratory post-hoc models including sTNF-R1, CRP, and age, classified 8 week culture status with promising accuracy.

Bloodborne viral infections in patients attending an emergency room in Mexico City: estimate of seroconversion probability in healthcare workers after an occupational exposure.

The frequency of hepatitis C (HCV), hepatitis B (HBV), human immunodeficiency virus (HIV), and human T-cell lymphotropic virus (HTLV) I/II was determined in the emergency room of a teaching hospital. Of 909 patients, 19% had at least one infection; 7.8% had HCV, 6.9% HBV, 3.3% HIV, and 2.8% HTLV I/II. The probability that a healthcare worker would have an accident with an infected patient and seroconvert was 4.99 to 24.9 per 100,000 venipunctures for HBV, 5.6 to 8.4 for HCV, and 0.12-0.16 for HIV in our emergency room.

[Microsporidiasis in AIDS patients with chronic diarrhea. Expieriences at the National Institute of Nutrition "Salvador Zubrirán"]. / Microsporidiasis en pacientes con SIDA y diarrea crónica. Experiencia en el Instituto Nacional de la Nutrición "Salvador Zubirán".

BACKGROUND: Microsporidium sp. has been considered as a rare cause of diarrhea in AIDS patients. However, the improvement of some histochemical stains in the analysis of small bowel biopsies has shown an increase in its prevalence. In Mexico there are no series reporting intestinal microsporidiasis. DESIGN: Small bowel biopsies of 98 patients with AIDS and chronic diarrhea stained with HE and Giemsa were reviewed (January 1987-December 1994). The clinical, demographic and laboratory information was obtained from the clinical charts. RESULTS: In 50 patients an opportunistic microorganism was identified in the small bowel biopsy (51%). Microsporidium sp. was identified in 30 patients (31%). The clinical charts were reviewed in all but six cases. Of the 24 patients with microsporidiasis as the cause of diarrhea, 17 were male and seven female with a median age, of 33 years, old. Homosexuality was the main risk factor in males (11/17), and blood transfusion in females (4/7). A low socioeconomical classification was found in 75% cases. The initial manifestation of AIDS was diarrhea in 16/24 (67%), CD4 count cell below 200 mm3 was identified in 13/24 patients and more than 200 mm3 in 2/24. The stool examination and the original histologic interpretations were negative for Microsporidium sp. Lymphoplasmocytic inflammatory infiltrate with eosinophils in the lamina propia and atrophy was frequently seen. A pale red and gray color was observed in spore and merogonial phases of Microsporidium stained with Giemsa. CONCLUSION: Microsporidium sp. was present as the only pathogen in 31% of the small bowel biopsies reviewed by light microscopy. Diarrhea due to Microsporidium sp. is frequently seen in advanced stages of AIDS with CD4 count cell below 200 mm3 Giemsa stain in the evaluation of small biopsies is a cheap and useful method to, identify Microsporidium sp.

Sublineages of lineage 4 (Euro-American) Mycobacterium tuberculosis differ in genotypic clustering.

SETTING: Mycobacterium tuberculosis is classified into six phylogenetic lineages, each of which can be divided into sublineages. Sublineages of the same lineage have phenotypic differences, including their capacity to cause disease (pathogenicity). OBJECTIVE: 1) To test the hypothesis that different sublineages of lineage 4, which causes most of the tuberculosis (TB) in the United States, have varying ability to cause secondary cases as determined by genotypic clustering, a proxy for pathogenicity; and 2) to determine if spoligotype and mycobacterial interspersed repetitive units (MIRU) typing could infer sublineage. DESIGN: We included TB cases caused by lineage 4 strains from our community-based study in San Francisco. Sublineage was determined by regions of difference. Genotypic clustering was determined by insertion sequence 6110 and polymorphic guanine-cytosine-rich sequence. Associations between sublineages and patient characteristics were evaluated with adjusted and unadjusted analyses. RESULTS: The most frequent sublineage was H37Rv-like. In the adjusted analysis, sublineage 183 was associated with clustering and homelessness. We found that strains from different sublineages had convergent spoligotype and MIRU types. CONCLUSIONS: Sublineage 183 is associated with genotypic clustering, evidence of its being more able to cause secondary cases than the other lineage 4 sublineages. This finding suggests that bacterial factors contribute to the pathogenesis of TB. Spoligotype and MIRU type cannot be used to infer sublineage.

Strain classification of Mycobacterium tuberculosis: congruence between large sequence polymorphisms and spoligotypes.

Spoligotyping is used in molecular epidemiological studies, and signature patterns have identified strain families. However, homoplasy occurs in the markers used for spoligotyping, which could lead to identical spoligotypes in phylogenetically unrelated strains. We determined the accuracy of strain classification based on spoligotyping using the six large sequence and single nucleotide polymorphisms-defined lineages as a gold standard. Of 919 Mycobacterium tuberculosis isolates, 870 (95%) were classified into a spoligotype family. Strains from a particular spoligotype family belonged to the same lineage. We did not find convergence to the same spoligotype. Spoligotype families appear to be sub-lineages within the main lineages.

Differences among sublineages of the East-Asian lineage of Mycobacterium tuberculosis in genotypic clustering.

SETTING: The East-Asian lineage of Mycobacterium tuberculosis is composed of five sublineages, and includes the strains from the Beijing spoligotype family. In some studies these strains were highly pathogenic, although other studies did not support this finding. OBJECTIVE: To determine if the sublineages of the East-Asian lineage of M. tuberculosis differ in their capacity to cause secondary cases, as assessed by genotypic clustering of isolates. DESIGN: In a population-based study of 545 patients with M. tuberculosis from the East-Asian lineage in San Francisco, we used DNA-based fingerprinting to identify genotypic clustering, which was compared among the different sublineages defined by large sequence polymorphism. RESULTS: Strains from sublineage 207 had the highest frequency of genotypic clustering. In the multivariate analysis, only patients born in the United States were associated with clustering. CONCLUSIONS: We found evidence in a univariate analysis that the different East-Asian sublineages of M. tuberculosis have different frequencies of genotypic clustering. The effect size for this difference was unchanged in multivariate analysis, although loss of observations due to missing data resulted in a non-significant P value. It is tantalizing to hypothesize that the different East-Asian sublineages may differ in their capacity to cause secondary cases.

User's guide to tuberculosis resources on the internet.

The World Wide Web has become a source of information for clinicians and researchers about virtually every aspect of tuberculosis (TB). We provide information about TB-related Internet portal sites. We classify selected TB-related Web pages according to user needs. The questions that we address are as follows: (1) Where can I find scientific information about TB? (2) Where can I find epidemiologic data? (3) Where can I find literature for laypeople? (4) Where can I find recommendations, guidelines, and clinical decision-making algorithms for management of TB? (5) Where can I find research databases? (6) Where can I find research groups? (7) Where can I find resources for research, teaching, and training? (8) Where can I find information about regulatory action? The total number of TB-related Web pages is immense, their scope is vast, and their content is perpetually changing. Nonetheless, the sites identified here provide the reader with a manageable number of entry points to this increasingly important resource.

Microarray analysis of pathogens and their interaction with hosts.

Microarrays are a promising technique for elucidating and interpreting the mechanistic roles of genes in the pathogenesis of infectious disease. Microarrays have been used to analyse the genetic polymorphisms of specific loci associated with resistance to antimicrobial agents, to explore the distribution of genes among isolates from the same and similar species, to understand the evolutionary relationship between closely related species and to integrate the clinical and genomic data. This technique has also been used to study host-pathogen interactions, mainly by identifying genes from pathogens that may be involved in pathogenicity and by surveying the scope of the host response to infection. The RNA expression profile of pathogens has been used to identify regulatory mechanisms that ensure gene expression in the appropriate environment, to hypothesize functions of hundreds of uncharacterized genes and to identify virulence genes that promote colonization or tissue damage. This information also has the potential to identify targets for drug design. Furthermore, microarrays have been used to investigate the mechanism of drug action and to delineate and predict adverse effects of new drugs. In this paper, we review the use of spotted and high-density oligonucleotide arrays to study the genetic polymorphisms of pathogens, host-pathogen interactions and whole-genome expression profiles of pathogens, as well as their use for drug discovery.

Detection of deleted genomic DNA using a semiautomated computational analysis of GeneChip data.

Genomic diversity within and between populations is caused by single nucleotide mutations, changes in repetitive DNA systems, recombination mechanisms, and insertion and deletion events. The contribution of these sources to diversity, whether purely genetic or of phenotypic consequence, can only be investigated if we have the means to quantitate and characterize diversity in many samples. With the advent of complete sequence characterization of representative genomes of different species, the possibility of developing protocols to screen for genetic polymorphism across entire genomes is actively being pursued. The large numbers of measurements such approaches yield demand that we pay careful attention to the numerical analysis of data. In this paper we present a novel application of an Affymetrix GeneChip to perform genome-wide screens for deletion polymorphism. A high-density oligonucleotide array formatted for mRNA expression and targeted at a fully sequenced 4.4-million-base pair Mycobacterium tuberculosis standard strain genome was adapted to compare genomic DNA. Hybridization intensities to 111,000 probe pairs (perfect complement and mismatch complement) were measured for genomic DNA from a clinical strain and from a vaccine organism. Because individual probe-pair hybridization intensities exhibit limited sensitivity/specificity characteristics to detect deletions, data-analytical methodology to exploit measurements from multiple probes in tandem locations across the genome was developed. The TSTEP (Tandem Set Terminal Extreme Probability) algorithm designed specifically to analyze the tandem hybridization measurements data was applied and shown to discover genomic deletions with high sensitivity. The TSTEP algorithm provides a foundation for similar efforts to characterize deletions in many hybridization measures in similar-sized and larger genomes. Issues relating to the design of genome content screening experiments and the implications of these methods for studying population genomics and the evolution of genomes are discussed.

Comparing genomes within the species Mycobacterium tuberculosis.

The study of genetic variability within natural populations of pathogens may provide insight into their evolution and pathogenesis. We used a Mycobacterium tuberculosis high-density oligonucleotide microarray to detect small-scale genomic deletions among 19 clinically and epidemiologically well-characterized isolates of M. tuberculosis. The pattern of deletions detected was identical within mycobacterial clones but differed between different clones, suggesting that this is a suitable genotyping system for epidemiologic studies. An analysis of genomic deletions among an extant population of pathogenic bacteria provided a novel perspective on genomic organization and evolution. Deletions are likely to contain ancestral genes whose functions are no longer essential for the organism's survival, whereas genes that are never deleted constitute the minimal mycobacterial genome. As the amount of genomic deletion increased, the likelihood that the bacteria will cause pulmonary cavitation decreased, suggesting that the accumulation of mutations tends to diminish their pathogenicity. Array-based comparative genomics is a promising approach to exploring molecular epidemiology, microbial evolution, and pathogenesis.

rpoB Gene mutations in rifampin-resistant Mycobacterium tuberculosis identified by polymerase chain reaction single-stranded conformational polymorphism.

The use of polymerase chain reaction-single-stranded conformational polymorphism (PCR-SSCP) to study rpoB gene mutations in rifampin-resistant (RIFr) Mycobacterium tuberculosis has yielded contradictory results. To determine the sensitivity of this method, we analyzed 35 RIFr strains and 11 rifampin-susceptible (RIFs) strains, using the DNA sequencing of the core region of rpoB for comparison. Of the RIFr, 24 had a PCR-SSCP pattern identical to that of H37Rv; the other 11 had four different patterns. The 11 RIFs had PCR-SSCP patterns identical to that of H37Rv. The sensitivity of the assay was 31.4%; its specificity was 100%. We observed a strong correlation between the degree of resistance and the type of mutation.