Inhibition of secretion of hepatitis B surface antigen by a related presurface polypeptide.

The presurface (preS) proteins of hepatitis B virus are structural components of the viral envelope that may play important roles in virion assembly and infectivity. They are specified by a large open reading frame that includes the coding region for the major surface (S) protein in its 3' half. Translation of the preS proteins initiates upstream from the S region, giving rise to proteins that are composed of the S domain and an additional 163 (preS1) or 55 (preS2) amino acids. Little is known about the biosynthesis and assembly of these proteins. The expression of the S and preS1 proteins was examined by transfecting cultured mammalian cells with viral DNA and injecting synthetic messenger RNA's into Xenopus oocytes. In contrast to the proteins encoded by the S region, the preS1 proteins are not detectably secreted into the culture medium. Furthermore, when the S and preS1 proteins are synthesized together, secretion of the S proteins is specifically and strongly inhibited. The results suggest a unique molecular interaction during secretion of the S and preS proteins that may be important for virus assembly.

Detection of Borrelia burgdorferi DNA in museum specimens of Ixodes dammini ticks.

In order to investigate the potential for Borrelia burgdorferi infection before the recognition of Lyme disease as a clinical entity, the polymerase chain reaction (PCR) was used to examine museum specimens of Ixodes dammini (deer ticks) for the presence of spirochete-specific DNA sequences. One hundred and thirty-six archival tick specimens were obtained representing various continental U.S. locations; DNA sequences characteristic of modern day isolates of B. burgdorferi were detected in 13 1940s specimens from Montauk Point and Hither Hills, Long Island, New York. Five archival specimens of Dermacentor variabilis (dog tick) from the same collection and 118 Ixodes specimens from other endemic and nonendemic sites were negative. These data suggest that the appearance of the Lyme disease spirochete in suitable arthropod vectors preceded, by at least a generation, the formal recognition of this disease as a clinical entity in the United States.

South African women's perspectives on self-sampling for cervical cancer screening: A mixed-methods study.

BACKGROUND: Self-sampling as a method of screening for cervical cancer and its precursors is an attractive option for low-resource settings. However, to allow successful integration of self-sampling into national screening programmes, it is necessary to understand women's perceptions and beliefs surrounding this method of sampling the cervix. OBJECTIVES: To explore women's attitudes to self-collection of samples for cervical screening in a low-resource setting in South Africa (SA). METHODS: Mixed methods were used to meet the study objectives. We recruited women aged 30 - 65 years into a study in Cape Town, SA, to participate in a cross-sectional survey. All women collected a vaginal self-sample, and underwent visual inspection with acetic acid, colposcopy, and collection of cervical samples and appropriate histology specimens by a doctor. Women had a quantitative questionnaire-based exit interview. A subset of these women participated in focus group discussions (FGDs). RESULTS: A total of 822 women answered the exit survey questionnaire and 41 women participated in the FGDs. Most women from the survey had a positive perception of self-sampling, with 93.6% of the women reporting not feeling embarrassed and 89.4% reporting experiencing no discomfort at all when taking a self-sample. This was corroborated by the FGD participants, who found self-sampling easier, more comfortable and less embarrassing than clinician sampling. However, many women (64.7%) felt more confident when the sample was taken by a clinician, despite having a positive attitude towards self-sampling. In most cases this was because they thought that the clinician would take a better sample, as explained by the FGD participants. Although 93.9% of the women were willing to collect a self-sample, the women in the FGDs expressed a preference for doing so at the health facility rather than at home. There were many reasons for this, including the cost of returning to the clinic with the sample. CONCLUSIONS: Attitudes regarding self-sample collection were positive in this study population. Participants were willing to perform self-sampling, but expressed concerns regarding the quality of the specimen and the financial implications of returning to the clinic with it. Pilot implementation studies will be useful before this method of sampling is adopted and integrated into screening programmes.

Effect of anti-interleukin 12 treatment on murine lyme borreliosis.

The effect of anti-interleukin (IL-12 treatment on Lyme borreliosis in C3H/HeN (C3H) mice was assessed because other studies have implicated CD4+ T cell helper (Th) type 1 responses in the genesis of disease caused by Borrelia burgdorferi. Infection of inbred mice with B. burgdorferi results in varying degrees of arthritis: BALB/c mice develop mild disease and C3H mice develop severe arthritis that is most pronounced 2-4 wk after infection. Since IL-12 is a major inducer of Th1 responses, we blocked this cytokine in vivo in B. burgdorferi infected C3H mice, and evaluated the effects of treatment on the development of arthritis at the peak of acute joint inflammation (14 d) and in the resolution phase (60 d) of disease. As expected, intraperitoneal administration of an anti-IL-12 monoclonal antibody (mAb) to C3H mice resulted in a decrease in both IFN-gamma and B. burgdorferi-specific IgG2a in serum, indicative of diminished Th1 responses. No IL-4 production was detected in serum of anti-IL-12 mAb treated or control mice. IgG1 and IgG2b levels did not increase in B. burgdorferi infected mice treated with anti-IL-12 mAb compared with controls suggesting that Th2 responses were not affected. Nevertheless, CD4+ T cells from both control and anti-IL-12 mAb treated mice had similar in vitro responses to B. burgdorferi antigens. Treatment with anti-IL-12 mAb produced a significant reduction in peak arthritis severity, and an increase in the number of spirochetes in ear tissue. These data show that treatment of B. burgdorferi infected mice with anti-IL-12 mAb results in a reduction of the Th1 and/or innate immune responses in vivo and a reduction in the severity of acute murine Lyme arthritis.

Mechanism of 2-aminopurine mutagenesis in mouse T-lymphosarcoma cells.

We investigated the mechanism of action of 2-aminopurine (Apur) in eucaryotic cells. By analogy with studies in procaryotic systems, the base analog is presumed to incorporate into DNA predominantly opposite T where, upon subsequent DNA replication, it can mispair with C, inducing an A:T leads to G:C transition. This model predicts that Apur-induced mutagenesis will be enhanced by factors that favor formation of Apur-C mispairs, e.g., high levels of dCTP or low levels of TTP. We describe the use of a mutant T-lymphosarcoma cell line, AraC-6-1, which has an abnormally high dCTP pool and a low TTP pool, to test this prediction. AraC-6-1 cells were three- to fivefold more mutable by Apur than their parental cell line, NSU-1. This enhanced mutability by Apur could not be explained by altered incorporation of 3H-labeled Apur, by generally impaired ability to repair DNA damage, or by a direct effect of Apur on the endogenous deoxynucleotide pools. The addition of 10 microM thymidine to the growth medium of AraC-6-1 cells lowered their high dCTP pool (two- to threefold), raised the TTP pool (two- to threefold), and abolished their enhanced mutability by Apur. Further manipulation to produce an abnormally high TTP/dCTP ratio suppressed Apur-induced mutagenesis (8- to 10-fold) in both AraC-6-1 and NSU-1 cells. These observations support the hypothesis that Apur induces A:T leads to G:C transitions in mammalian cells by a mispairing mechanism.

Ribosomal DNA sequencing as a tool for identification of bacterial pathogens.

Conventional methods for the identification and characterization of clinical isolates of bacterial pathogens sometimes fall short when such isolates exhibit unusual phenotypic profiles. Recent advances in DNA sequencing technology have greatly enhanced the ability of the microbiologist to determine the identity of a bacterial isolate. Given the relative objectivity of DNA sequence information and growing availability of sequence information databases, a significant movement is now afoot to use molecular methods for the identification of clinical pathogens.

Human papillomavirus type 16 integrations in cervical tumors frequently occur in common fragile sites.

The development of cervical cancer is highly associated with human papillomavirus (HPV) infection. HPV integration into the genome of infected cervical cells is temporally associated with the acquisition of the malignant phenotype. A relationship between the sites of HPV integration in cervical cancer and the position of the common fragile sites (CFSs) has been observed at the cytogenetic level. To explore this relationship at the molecular level, we used a PCR-based method to rapidly isolate cellular sequences flanking the sites of HPV16 integrations in primary cervical tumors. Human bacterial artificial chromosome clones were isolated based on these flanking sequences and used as probes for fluorescence in situ hybridization on metaphases derived from cells cultured in the presence of aphidicolin. Our data demonstrate that HPV16 integrations in cervical tumors frequently occur within CFSs at the molecular level. In addition, we have determined the precise molecular locations of the CFSs FRA6C and FRA17B.

L552S, an alternatively spliced isoform of XAGE-1, is over-expressed in lung adenocarcinoma.

Using a combination of cDNA subtraction and microarray analysis, we report here the identification and characterization of L552S, an over-expressed, alternatively spliced isoform of XAGE-1 in lung adenocarcinoma. Real-time RT-PCR analysis shows that L552S is expressed at levels greater than 10-fold in 12 of 25 lung adenocarcinoma tumors compared with the highest expression level found in all normal tissues tested. L552S is expressed in both early and late stages of lung adenocarcinoma, but it was not detected in large cell carcinoma, small cell carcinoma, or atypical lung neuroendocrine carcinoid. The full-length cDNA for L552S comprises 770 bp and encodes a polypeptide of 160 amino acids. C-terminal 94 amino acids of L552S are identical to a cancer testis antigen, XAGE-1, found in Ewing's sarcoma. Genomic sequence analysis has revealed that L552S and XAGE-1 are alternatively spliced isoforms, and expression of both L552S and XAGE-1 isoforms are present in lung adenocarcinoma. Immunohistochemistry analysis using affinity purified L552S polyclonal antibodies demonstrated specific nuclear staining in 10 of 12 lung adenocarcinoma samples. Furthermore, antibody responses to recombinant L552S protein were observed in seven of 17 lung pleural effusion fluids of lung cancer patients. These results strongly imply that L552S protein is immunogenic and suggest that it might have use as a vaccine target for lung cancer.

A first-tier rapid assay for the serodiagnosis of Borrelia burgdorferi infection.

BACKGROUND: The present recommendation for the serologic diagnosis of Lyme disease is a 2-tier process in which a serum sample with a positive or equivocal result by an enzyme-linked immunosorbent assay (ELISA) or immunofluorescent assay is then followed by supplemental testing by Western blot. Our laboratory has developed recombinant chimeric proteins composed of key Borrelia epitopes. These novel antigens are consistent and are easily standardized. METHODS: We adapted these recombinant proteins into a new immunochromatographic format that can be used as a highly sensitive and specific first-tier assay that can be used to replace the ELISA or immunofluorescent assay. RESULTS: This rapid test was equally sensitive (P>.05) and more specific (P<.05) than a frequently used commercial whole cell ELISA. The overall clinical accuracy achieved on agreement studies among 3 Lyme research laboratories on clinically defined serum panels was shown to be statistically equivalent to the commercial ELISA. The assay can detect anti-Borrelia burgdorferi antibodies in either serum or whole blood. CONCLUSION: This sensitive and specific rapid assay, which is suited for the physician's office, streamlines the 2-tier system by allowing the physician to determine if a Western blot is necessary at the time of the initial office visit.

A case-control study to assess possible triggers and cofactors in chronic fatigue syndrome.

PURPOSE: To assess possible triggers and cofactors for chronic fatigue syndrome (CFS) and to compare levels of selected cytokines between cases and an appropriately matched control group. PATIENTS AND METHODS: We conducted a case-control study of 47 cases of CFS obtained through a regional CFS research program maintained at a tertiary care medical center. One age-, gender-, and neighborhood-matched control was identified for each case through systematic community telephone sampling. Standardized questionnaires were administered to cases and controls. Sera were assayed for transforming growth factor-beta (TGF-beta), interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha, and antibody to Borrelia burgdorferi and Babesia microti. RESULTS: Cases were more likely to have exercised regularly before illness onset than controls (67% versus 40%; matched odds ratio (MOR) = 3.4; 95% CI = 1.2 to 11.8; P = 0.02). Female cases were more likely to be nulliparous prior to onset of CFS than controls (51% versus 31%; MOR = 8.0; 95% CI = 1.03 to 170; P = 0.05). History of other major factors, including silicone-gel breast implants (one female case and one female control), pre-morbid history of depression (15% of cases, 11% of controls) and history of allergies (66% of cases, 51% of controls) were similar for cases and controls. However, cases were more likely to have a diagnosis of depression subsequent to their diagnosis of CFS compared to a similar time frame for controls (MOR = undefined; 95% CI lower bound = 2.5; P < 0.001). Positive antibody titers to B burgdorferi (one case and one control) and B microti (zero cases and two controls) were also similar. CONCLUSIONS: Further investigation into the role of prior routine exercise as a cofactor for CFS is warranted. This study supports the concurrence of CFS and depression, although pre-morbid history of depression was similar for both groups.

Transfer of porcine endogenous retrovirus across hollow fiber membranes: significance to a bioartificial liver.

BACKGROUND: A porcine endogenous retrovirus (PERV) capable of infecting human cells has been identified. This study was designed to determine whether hollow fiber membranes, such as those used in a bioartificial liver, block the transfer of PERV. METHODS: Three hollow fiber cartridges (HFCs) were studied in duplicate: cellulose fibers with 70 kD nominal molecular weight cut-off (MWCO), polysulfone fibers with 400 kD MWCO, and mixed cellulose fibers with 200 nm porosity. PK15 cells (porcine kidney cell line), known to produce PERV, were grown in the intraluminal compartment of HFCs fiber cartridges. Samples of medium were collected from both intraluminal and extraluminal compartments of the HFCs fiber cartridge during 14 days of culture. Samples were screened for PERV using reverse transcription polymerase chain reaction. All positive samples were tested for PERV infectivity in human 293 cells. RESULTS: PERV was detected in all samples from the intraluminal space and all intraluminal samples seemed to infect 293 cells. All extraluminal samples from the fibers of 200 nm porosity tested positive for PERV. Detection of PERV in the extraluminal space was delayed by fibers of 400 kD MWCO and 70 kD MWCO until at least day 3 and day 7, respectively, after inoculation of PK15 cells. Positive extraluminal samples from fibers of 400 kD MWCO and 70 kD MWCO did not infect 293 cells. CONCLUSION: Pore size, membrane composition, and duration of exposure influenced the transfer of PERV across HFCs. Some HFCs decrease the risk of viral exposure to patients during bioartificial liver therapy.

Relationship between hepatitis C genotype and severity of recurrent hepatitis C after liver transplantation.

BACKGROUND: Recurrence of hepatitis C virus (HCV) infection after liver transplantation is universal, but the relationship between hepatitis C genotype and posttransplant outcome has been controversial. The aim of this study was to assess the relationship between hepatitis C genotype on posttransplant frequency of recurrent hepatitis, histologic severity of recurrence, and progression to cirrhosis. METHODS: We studied 42 HCV RNA positive patients who received transplants between 1985 and 1994. Sera were tested for HCV RNA and protocol liver biopsies were in obtained the posttransplant period. Biopsies were scored according to the histologic activity index (HAI) and staged in a blinded fashion. RESULTS: The distribution of hepatitis C genotypes distribution was as follows: 1a, 19 (45%); 1b, 17 (40%); 2b, 3 (7%); and 1 each of 2a, 3a, and 4a. There was histologic evidence of hepatitis in 38 of 42 (90.4%) of patients. Hepatitis C was mild, moderate, or severe (HAI>3) in 38% of grafts and minimal (HAI 0-3) in 62%. Overall HAI scores and histologic stage were higher in the genotype 1b group. Six of 17 (35%) genotype 1b patients had cirrhosis compared with 2 of 25 (8%) in the non-1b genotype group. CONCLUSIONS: (1) Histologic evidence of recurrent hepatitis C is seen in 90% of liver allografts; (2) Histologic hepatitis C recurs with similar frequency in genotype 1b and non-1b recipients; (3) Genotype 1b is associated with more severe histologic disease recurrence than non-1b genotypes; (4) Genotype 1b appears to be associated with a higher degree of posttransplant fibrosis and cirrhosis than non-1b genotypes.

Hepatitis G virus infection in patients transplanted for cryptogenic cirrhosis: red flag or red herring?

BACKGROUND: The significance of hepatitis G (HGV) infection in liver transplant recipients is not known. We set out to determine the pre-orthotopic liver transplantation (OLT) prevalence, the pre- and postoperative viral titers of HGV, and the allograft histology in patients infected with HGV who underwent OLT for cryptogenic cirrhosis. METHODS: HGV RNA was measured using a research-based branched DNA assay. The assay used a target-specific probe set that was based on the 5'-untranslated region of the HGV genome. Allograft histology was assessed with protocol liver biopsies in all patients who survived longer than 6 months. RESULTS: The preoperative prevalence of HGV infection in recipients transplanted for cryptogenic cirrhosis was 26%. Thirty-seven percent (12 of 33) of recipients who had serum available in the first postoperative month had HGV infection. Mean HGV RNA levels were 9.8 (+/-4.2) (viral molecular equivalents/ml x 10[6]) before OLT and 37.5 (+/-10.7) at 1 year after OLT. In 4 of the 11 cryptogenic recipients in whom HGV RNA was detectable in the first postoperative month, HGV RNA fell to undetectable levels at the most recent follow-up (mean 70 months). Of the five cryptogenic recipients who continue to have measurable HGV RNA, three have unexplained hepatitis histologically. CONCLUSIONS: These findings suggest the following: 1) The prevalence of HGV infection in patients undergoing OLT for cryptogenic cirrhosis is about 25%. 2) In recipients persistently infected with HGV, mean HGV RNA titers increase after OLT. 3) HGV RNA becomes undetectable in about one third of recipients who had detectable HGV RNA in the first month after OLT. 4) Hepatitis of uncertain etiology occurs in 60% (3 of 5) of persistently HGV-infected cryptogenic recipients.

Hepatitis C genotypes: current trends and future implications.

OBJECTIVE: To review the geographic distribution and current understanding of hepatitis C virus (HCV) genotypes in regard to liver disease activity and response to treatment. MATERIAL AND METHODS: We review the relevant medical literature and discuss our recent findings relative to chronic HCV infection and the importance of HCV genotypes. RESULTS: HCV genotypes 1a and 1b are the most commonly found genotypes in patients with chronic HCV in the United States. Infection with HCV genotype 1b may be associated with more severe liver disease and may have a higher risk for the development of hepatocellular carcinoma. HCV genotype 2b seemed to be the most sensitive and HCV genotype 1b was the least sensitive to interferon therapy. CONCLUSION: The identification of the infectious HCV genotype may be beneficial in clinical settings and may assist in the selection of patients who would benefit from interferon treatment.

Genotype-dependent serologic reactivities in patients infected with hepatitis C virus in the United States.

OBJECTIVE: To evaluate the serologic reactivities in patients infected with different hepatitis C virus (HCV) genotypes to four HCV proteins that are components of the second-generation recombinant immunoblot assay. MATERIAL AND METHODS: Serum samples from 36 patients with chronic HCV infection were obtained. RNA was extracted by using chaotropic lysis and isopropanol precipitation. Reverse-transcriptase polymerase chain reaction of the NS-5 region was performed, followed by automated single-pass dideoxy sequencing of desalted amplification products. Classification of isolated HCV subtypes was based on Simmonds' system. All samples were tested for antibodies to proteins 5-1-1, C100-3, C33c, and C22-3 with the second-generation recombinant immunoblot assay. RESULTS: Reactivity to protein 5-1-1 was significantly lower for patients with genotypes 2b and 3a than for those infected with HCV types 1a or 1b (P < 0.05). Antibody reactivity to the C100-3 protein was also reduced in patients infected with HCV types 2b and 3a. CONCLUSION: These data indicate that the genotype-dependent differences in serologic reactivities are substantial among patients with chronic HCV infection.

Viral genotypes as determinants of autoimmune expression in chronic hepatitis C.

OBJECTIVE: To correlate viral genotypes with the immune manifestations of chronic hepatitis C and evaluate the effect of immune features on disease expression and response to antiviral treatment. DESIGN: We undertook a retrospective analysis of 67 patients with chronic hepatitis C. MATERIAL AND METHODS: Patients were selected for study if they had been screened for autoantibodies and concurrent immune diseases and if viral genotyping had been performed or was possible. Concurrent immune manifestations and responses to interferon therapy were determined. RESULTS: Of the 67 patients, 18 (27%) had one or more immune features. Immune manifestations occurred as commonly in patients with genotype 1 as in those with other genotypes (30% versus 14%; P = 0.3). Concurrent immune features did not distinguish patients, and responses to interferon therapy were similar between patients with and those without immune manifestations. None of the 14 patients with concurrent immune diseases or high-titer autoantibodies (serum titers, 1:320 or more) entered remission during interferon treatment. In contrast, 6 of 53 patients without concurrent immune diseases and no or low-titer autoantibodies had treatment-related remission. These differences, however, were not statistically significant (0% versus 11%; P = 0.3). CONCLUSION: Autoantibodies and concurrent immune diseases are not associated with a particular viral genotype, clinical profile, or treatment outcome. Larger studies are necessary for complete assessment of the influence of prominent immune manifestations on treatment response.

Coinfection with Babesia microti and Borrelia burgdorferi in a western Wisconsin resident.

A 68-year-old woman, who had not traveled outside of western Wisconsin, was hospitalized after 4 weeks of chills, fevers, myalgias, neuralgias in her right arm, and pain in the right upper quadrant of her abdomen. Physical examination revealed hepatosplenomegaly, and laboratory studies showed anemia, thrombocytopenia, increased aspartate transaminase level, and microscopic hematuria. Wright's stain of a blood smear revealed intraerythrocytic organisms consistent with Babesia species. A polymerase chain reaction of whole blood specimens along with an increased serologic titer confirmed the diagnosis of Babesia microti. Indirect immunofluorescent antibody serology and Western blot analysis revealed a simultaneous infection with Borrelia burgdorferi. Coinfection with B. microti and B. burgdorferi may occur in endemic areas where both organisms are carried by the same tick vector, Ixodes scapularis. The intensity and duration of illness seem to be greatest in patients with concurrent infection.

Human babesiosis.

OBJECTIVE: To describe a case of human babesiosis and review the literature on the disease. MATERIAL AND METHODS: We describe a 62-year-old man with babesiosis, outline his clinical course and response to therapy, and discuss the use of the polymerase chain reaction for the diagnosis and monitoring of the infection. RESULTS: The onset of the disease was insidious, with fatigue, fever, weight loss, intermittently discolored urine, and anemia. Computed tomography of the abdomen revealed a small, shrunken spleen with an irregular border. With treatment, the symptoms gradually resolved. Although peripheral blood smears were negative soon after therapy, Babesia microti DNA was detected by polymerase chain reaction 53 days after initial examination. CONCLUSION: The development of improved methods for diagnosis, including indirect immunofluorescent antibody assays and the polymerase chain reaction, provides more sensitive detection of the parasitemia associated with babesiosis. Use of these methods may help to delineate the complete clinical spectrum of this infection and its geographic distribution in the United States.

GB virus-C infection in type 1 autoimmune hepatitis.

OBJECTIVE: To assess the frequency and significance of GB virus-C infection in type 1 autoimmune hepatitis. MATERIAL AND METHODS: Serum specimens from 94 patients with type 1 autoimmune hepatitis were tested for GB virus-C RNA by reverse transcription and polymerase chain reaction. Serum samples from 50 normal subjects were also assessed. RESULTS: Three of the 94 specimens from patients with autoimmune hepatitis were positive for GB virus-C RNA in comparison with none of the 50 control samples (3% versus 0%; P = 0.5). Two patients were seropositive after variceal hemorrhage and blood transfusion, including one patient who clearly acquired the infection in this fashion. One patient had no epidemiologic basis for his seropositivity. Viremia was prolonged in all infected patients (mean duration, 69 +/- 23 months; range, 36 to 113); however, no clinical features suggested a concurrent viral infection, and mortality was similar to that among the uninfected counterparts (33% versus 8%; P = 0.2). Liver transplantation was more common in the infected patients (67% versus 9%; P = 0.03), but the duration of disease was also longer in these patients (277 +/- 29 months versus 106 +/- 9 months; P = 0.0008). Clinical features and immediate responses to corticosteroid therapy were similar in both groups. CONCLUSION: GB virus-C RNA is found infrequently in type 1 autoimmune hepatitis, and GB virus-C is unlikely to be an important etiologic agent or prognostic determinant.

Prospective evaluation of the utility of molecular techniques for diagnosing nosocomial transmission of multidrug-resistant tuberculosis.

OBJECTIVE: To compare molecular techniques with conventional diagnostic methods for evaluating nosocomial transmission of multidrug-resistant tuberculosis (MDR-TB). DESIGN: We conducted a 12-week postexposure inception cohort study of health-care personnel who had been exposed to a patient with MDR-TB. MATERIAL AND METHODS: In addition to baseline and follow-up tuberculin skin tests and chest roentgenography, weekly pulmonary specimens were evaluated by (1) auramine-rhodamine fluorescent staining, (2) culture for mycobacteria, and (3) polymerase chain reaction (PCR) to amplify IS6110, a nucleic acid insertion sequence unique to the Mycobactrium tuberculosis complex. RESULTS: The index patient's isolate of M. tuberculosis showed a mutation in codon 531 of the RNA polymerase beta subunit (rpoB) gene of M. tuberculosis, which is associated with rifampin resistance and considered a marker for this MDR-TB strain. All pulmonary and gastric specimens from study participants had negative auramine stains and cultures for mycobacteria, One person, however, had separate specimens with repeatedly positive PCR results for IS6110 sequences, but the specimens contained a wild-type M. tuberculosis rpoB codon 531 dissimilar from the index patient's strain. CONCLUSION: Although both molecular and conventional testing showed that no exposed person was infected with the MDR-TB strain, molecular test results were available sooner and seemed more sensitive for detecting M. tuberculosis in one exposed person, presumably in a preinfection or "colonized" stage. Molecular methods provided information that helped distinguish this person's M. tuberculosis strain from the index patient's MDR-TB strain. Additional prospective studies should assess the value of these molecular techniques in similar clinical settings.