David Y Graham

Michael E. DeBakey VA Medical Center, Houston, Texas, United States

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Publications (622)4651.75 Total impact

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    ABSTRACT: Excessive and inappropriate immune responses are the hallmark of several autoimmune disorders, including the inflammatory bowel diseases (IBD): Crohn’s disease (CD) and ulcerative colitis (UC). A complex etiology involving both environmental and genetic factors influences IBD pathogenesis. The role of microRNAs (miRNAs), noncoding RNAs involved in regulating numerous biological processes, to IBD pathology, in terms of initiation and progression, remains ill-defined. In the present study, we evaluated the relationship between colon, peripheral blood, and saliva whole miRNome expression in IBD patients and non-inflammatory bowel disease (non-IBD) controls to identify miRNAs that could discriminate CD from UC. Quantitative real-time PCR (qRT-PCR) was used to validate and assess miRNA expression. Microarray analysis demonstrated that upwards of twenty six miRNAs were changed in CD and UC colon biopsies relative to the non-IBD controls. CD was associated with the differential expression of 10 miRNAs while UC was associated with 6 miRNAs in matched colon tissues. CD was associated with altered expression of 6 miRNAs while UC was associated with 9 miRNAs in whole blood. Expression of miR-101 in CD patients and miR-21, miR-31, miR-142-3p, and miR-142-5p in UC patients were altered in saliva. Our results suggest that there is specific miRNA expression patterns associated with UC versus CD in three separate tissue/body fluids (colon, blood, and saliva). Further, the aberrant miRNA expression profiles indicate that miRNAs may be contributory to IBD pathogenesis, or at least reflect the underlying inflammation. Scrutinizing miRNA expression in saliva and blood samples may be beneficial in monitoring or diagnosing disease in IBD patients. A panel of miRNAs (miR-19a, miR-21, miR-31, miR-101, miR-146a, and miR-375) may be used as markers to identify and discriminate between CD and UC.
    BMC Immunology 12/2015; 16(1). DOI:10.1186/s12865-015-0069-0 · 2.48 Impact Factor
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    ABSTRACT: Importance: Our research establishes HIEs as nontransformed cell culture models to understand human intestinal physiology, pathophysiology and the epithelial response, including host restriction to gastrointestinal infections such as HRV infection. HRVs remain a major worldwide cause of diarrhea-associated morbidity and mortality in children ≤ age five. Current in vitro models of rotavirus infection rely primarily on the use of animal rotaviruses because HRV growth is limited in most transformed cell lines and animal models. We demonstrate that HIEs are novel, diverse cellular and physiologically relevant epithelial cultures, which recapitulate in vivo properties of HRV infection. HIEs will allow the study of HRV biology, including human host-pathogen and live, attenuated vaccine interactions, host and cell-type restriction, viral-induced fluid secretion, cell-cell communication within the epithelium, and the epithelial response to infection in cultures from genetically diverse individuals. Finally, drug therapies to prevent/treat diarrheal disease can be tested in these physiologically active cultures.
    Journal of Virology 10/2015; DOI:10.1128/JVI.01930-15 · 4.44 Impact Factor
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    Wei Zhang · Qi Chen · Xiao Liang · Wenzhong Liu · Shudong Xiao · David Y Graham · Hong Lu ·
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    ABSTRACT: Objective: To evaluate the efficacy and tolerability of replacing tetracycline with amoxicillin in bismuth quadruple therapy. Design: Subjects who were infected with Helicobacter pylori and naïve to treatment were randomly (1:1) assigned to receive a 14-day modified bismuth quadruple therapy: lansoprazole 30 mg, amoxicillin 1 g, bismuth potassium citrate 220 mg (elemental bismuth), twice a day with metronidazole 400 mg four times a day (metronidazole group) or clarithromycin 500 mg twice a day (clarithromycin group). Six weeks after treatment, H. pylori eradication was assessed by (13)C-urea breath test. Antimicrobial susceptibility was assessed by the twofold agar dilution method. This was a non-inferiority trial. Results: Two hundred and fifteen subjects were randomised. Metronidazole and clarithromycin containing regimens achieved high cure rates: 94 of 97 (96.9%, 95% CI 93.5% to 100%) and 93 of 98 (94.9%, 95% CI 90.5% to 99.3%) by per-protocol and 88.9% (95% CI 83.0% to 94.8%) and 88.8% (95% CI 82.8% to 94.8%) by intention-to-treat, respectively. Amoxicillin, metronidazole and clarithromycin resistance rates were 1.5%, 45.5% and 26.5%, respectively. Only clarithromycin resistance reduced treatment success (eg, susceptible 98.6%, resistant 76.9%, p=0.001). Adverse events were more common in the metronidazole group. Conclusions: These results suggest that amoxicillin can substitute for tetracycline in modified 14 day bismuth quadruple therapy as first-line treatment and still overcome metronidazole resistance in areas with high prevalence of metronidazole and clarithromycin resistance. Using clarithromycin instead of metronidazole was only effective in the presence of susceptible strains. Trial registration number: NCT02175901.
    Gut 09/2015; 64(11). DOI:10.1136/gutjnl-2015-309900 · 14.66 Impact Factor
  • Akiko Shiotani · David Y Graham ·

    Gastroenterology clinics of North America 09/2015; 44(3):xv-xvi. DOI:10.1016/j.gtc.2015.07.001 · 2.82 Impact Factor
  • Akiko Shiotani · David Y. Graham ·

  • Cancer Research 08/2015; 75(15 Supplement):4591-4591. DOI:10.1158/1538-7445.AM2015-4591 · 9.33 Impact Factor
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    ABSTRACT: To present results of the Kyoto Global Consensus Meeting, which was convened to develop global consensus on (1) classification of chronic gastritis and duodenitis, (2) clinical distinction of dyspepsia caused by Helicobacter pylori from functional dyspepsia, (3) appropriate diagnostic assessment of gastritis and (4) when, whom and how to treat H. pylori gastritis. Twenty-three clinical questions addressing the above-mentioned four domains were drafted for which expert panels were asked to formulate relevant statements. A Delphi method using an anonymous electronic system was adopted to develop the consensus, the level of which was predefined as ≥80%. Final modifications of clinical questions and consensus were achieved at the face-to-face meeting in Kyoto. All 24 statements for 22 clinical questions after extensive modifications and omission of one clinical question were achieved with a consensus level of >80%. To better organise classification of gastritis and duodenitis based on aetiology, a new classification of gastritis and duodenitis is recommended for the 11th international classification. A new category of H. pylori-associated dyspepsia together with a diagnostic algorithm was proposed. The adoption of grading systems for gastric cancer risk stratification, and modern image-enhancing endoscopy for the diagnosis of gastritis, were recommended. Treatment to eradicate H. pylori infection before preneoplastic changes develop, if feasible, was recommended to minimise the risk of more serious complications of the infection. A global consensus for gastritis was developed for the first time, which will be the basis for an international classification system and for further research on the subject. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
    Gut 07/2015; 64(9). DOI:10.1136/gutjnl-2015-309252 · 14.66 Impact Factor
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    ABSTRACT: To investigated the performance of the tissue resonance interaction method (TRIM) for the non-invasive detection of colon lesions. We performed a prospective single-center blinded pilot study of consecutive adults undergoing colonoscopy at the University Hospital in Sassari, Italy. Before patients underwent colonoscopy, they were examined by the TRIMprobe which detects differences in electromagnetic properties between pathological and normal tissues. All patients had completed the polyethylene glycol-containing bowel prep for the colonoscopy procedure before being screened. During the procedure the subjects remained fully dressed. A hand-held probe was moved over the abdomen and variations in electromagnetic signals were recorded for 3 spectral lines (462-465 MHz, 930 MHz, and 1395 MHz). A single investigator, blind to any clinical information, performed the test using the TRIMprob system. Abnormal signals were identified and recorded as malignant or benign (adenoma or hyperplastic polyps). Findings were compared with those from colonoscopy with histologic confirmation. Statistical analysis was performed by χ(2) test. A total of 305 consecutive patients fulfilling the inclusion criteria were enrolled over a period of 12 months. The most frequent indication for colonoscopy was abdominal pain (33%). The TRIMprob was well accepted by all patients; none spontaneously complained about the procedure, and no adverse effects were observed. TRIM proved inaccurate for polyp detection in patients with inflammatory bowel disease (IBD) and they were excluded leaving 281 subjects (mean age 59 ± 13 years; 107 males). The TRIM detected and accurately characterized all 12 adenocarcinomas and 135/137 polyps (98.5%) including 64 adenomatous (100%) found. The method identified cancers and polyps with 98.7% sensitivity, 96.2% specificity, and 97.5% diagnostic accuracy, compared to colonoscopy and histology analyses. The positive predictive value was 96.7% and the negative predictive value 98.4%. Among the 281 non-IBD subjects, there were 7 cases with discordant results (2.5%) between TRIMprob and the reference standard including 5 false positive results (1.8%) and 2 false negative (0.7%) results. The main limitation of the TRIMprob system is the need for trained operators. The study confirmed that TRIM provides rapid, accurate, convenient and noninvasive means to identify individuals most likely to benefit from colonoscopy.
    07/2015; 21(25):7851-9. DOI:10.3748/wjg.v21.i25.7851
  • David Y Graham ·
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    ABSTRACT: As a general rule, any clinical study where the result is already known or when the investigator(s) compares an assigned treatment against another assigned treatment known to be ineffective in the study population (e.g., in a population with known clarithromycin resistance) is unethical. As susceptibility-based therapy will always be superior to empiric therapy in any population with a prevalence of antimicrobial resistance >0%, any trial that randomizes susceptibility-based therapy with empiric therapy would be unethical. The journal Helicobacter welcomes susceptibility or culture-guided studies, studies of new therapies, and studies of adjuvants and probiotics. However, the journal will not accept for review any study we judge to be lacking clinical equipoise or which assign subjects to a treatment known to be ineffective, such as a susceptibility-based clinical trial with an empiric therapy comparator. To assist authors, we provide examples and suggestions regarding trial design for comparative studies, for susceptibility-based studies, and for studies testing adjuvants or probiotics. © 2015 John Wiley & Sons Ltd.
    Helicobacter 06/2015; 20(5). DOI:10.1111/hel.12244 · 4.11 Impact Factor
  • David Y. Graham · Sun-Young Lee ·
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    ABSTRACT: Bismuth triple therapy was the first effective Helicobacter pylori eradication therapy. The addition of a proton pump inhibitor helped overcome metronidazole resistance. Its primary indication is penicillin allergy or when clarithromycin and metronidazole resistance are both common. Resistance to the primary first-line therapy have centered on complexity and difficulties with compliance. Understanding regional differences in effectiveness remains unexplained because of the lack of studies including susceptibility testing and adherence data. We discuss regimen variations including substitutions of doxycycline, amoxicillin, and twice a day therapy and provide suggestions regarding what is needed to rationally and effectively use bismuth quadruple therapy. Published by Elsevier Inc.
    Gastroenterology clinics of North America 06/2015; 44(3). DOI:10.1016/j.gtc.2015.05.003 · 2.82 Impact Factor
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    ABSTRACT: Noroviruses are the leading cause of acute gastroenteritis worldwide, and norovirus vaccine prevention strategies are under evaluation. The immunogenicity of two doses of bivalent GI.1/GII.4 (50μg VLP of each strain adjuvanted with aluminum hydroxide and MPL) norovirus vaccine administered to healthy adults in a phase 1-2 double-blind, placebo-controlled trial was determined using virus-specific, serum total antibody ELISA, IgG, IgA and histoblood group antigen (HBGA) blocking assays. Trial participants subsequently received an oral live virus challenge with a GII.4 strain and vaccine efficacy results have been reported previously (D.I. Bernstein et al. J Infect Dis 211:870-878, 2015, doi:10.1093/infdis/jiu497). This report assesses the impact of pre-challenge serum antibody levels on infection and illness outcomes. Serum antibody responses were observed in vaccine recipients by all antibody assays, with first dose seroresponse frequencies ranging from 88-100% for the GI.1 antigen and from 69-84% for the GII.4 antigen. There was little increase in antibody level after the second vaccine dose. Among placebo subjects, higher pre-challenge serum anti-GII.4 HBGA-blocking and IgA antibody levels, but not IgG or total antibody levels, were associated with a lower frequency of virus infection and associated illness. Notably, some placebo subjects without measurable serum antibody pre-challenge did not become infected after norovirus challenge. In vaccinees, anti-GII.4 HBGA-blocking antibody levels >1:500 were associated with a lower frequency of moderate-to-severe vomiting or diarrheal illness. In this study, pre-challenge serum HBGA antibody titers correlated with protection in placebo subjects; however, other factors may impact the likelihood of infection and illness after virus exposure. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Clinical and vaccine Immunology: CVI 06/2015; 22(8). DOI:10.1128/CVI.00196-15 · 2.47 Impact Factor
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    ABSTRACT: Both cold-only snare and hot polypectomy snare are used for the removal of small colorectal polyps. To compare the outcome of cold snare polypectomy of small colorectal polyps with a snare exclusively designed as a cold snare versus cold snare polypectomy by using a traditional polypectomy snare. Prospective, randomized, controlled study. Municipal hospital in Japan. Patients with colorectal polyps 10 mm or smaller in diameter were randomized to dedicated cold snare (dedicated cold snare group) or traditional cold snare (traditional cold snare group). The primary outcome measure was complete resection rates by cold snaring based on pathological examination. Secondary outcomes included bleeding within 2 weeks after polypectomy and identification of submucosal arteries and injured arteries in the resected specimens. Seventy-six patients having 210 eligible polyps were randomized: dedicated cold snare group, N = 37 (98 polyps) and traditional cold snare group, N = 39 (112 polyps). Patient demographic characteristics including the number, size, and shape of the polyps removed were similar in the 2 groups. The complete resection rate was significantly greater with the dedicated cold than with the traditional cold snare (91% [89/98] vs 79% [88/112], P = .015), with a marked difference with 8- to 10-mm polyps, both flat and pedunculated. Immediate bleeding and hematochezia rates were similar (19% vs 21%, P = .86; 5.4% vs 7.7%, P = .69). No delayed bleeding occurred. Histology demonstrated a similar prevalence of arteries and injured arteries in the submucosa (33% [32/96] vs 30% [31/104], P = .59; 3.1% [3/96] vs 6.7% [7/104], P = .24). Small sample size, single-center study. Polypectomy by using a dedicated cold snare resulted in complete polyp removal more often than did cold snaring with a traditional snare, especially polyps 8 to 10 mm in diameter, whether flat or pedunculated. (Clinical trial registration number: NCT02036047.). Copyright © 2015 American Society for Gastrointestinal Endoscopy. Published by Elsevier Inc. All rights reserved.
    Gastrointestinal endoscopy 04/2015; 82(4). DOI:10.1016/j.gie.2015.02.012 · 5.37 Impact Factor

  • Gastroenterology 04/2015; 148(4):S-529. DOI:10.1016/S0016-5085(15)31768-6 · 16.72 Impact Factor
  • Ping-I Hsu · David Y. Graham ·

    Gastroenterology 04/2015; 148(4):S-420. DOI:10.1016/S0016-5085(15)31417-7 · 16.72 Impact Factor

  • Gastroenterology 04/2015; 148(4):S-529. DOI:10.1016/S0016-5085(15)31769-8 · 16.72 Impact Factor
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    ABSTRACT: Innate immunity plays important roles in the primary defense against pathogens, and epidemiological studies have suggested a role for Toll-like receptor (TLR) 1 in Helicobacter pylori susceptibility. Microarray analysis of gastric biopsy specimens from H. pylori-positive and uninfected subjects showed TLR10 messenger RNA (mRNA) levels were upregulated ∼15-fold in infected subjects and confirmed by the quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Immunohistochemistry showed increased TLR10 expression in the gastric epithelial cells of infected individuals. When H. pylori was co-cultured with NCI-N87 gastric cells, both TLR10 and TLR2 mRNA levels were upregulated. We compared the ability of TLR combinations to mediate nuclear factor-κB (NF-κB) activation. Compared to other TLR2 subfamily heterodimers, the TLR2/TLR10 heterodimer mediated the greatest NF-κB activation following exposure to heat-killed H. pylori or H. pylori lipopolysaccharide. We conclude that TLR10 is a functional receptor involved in the innate immune response to H. pylori infection and that the TLR2/TLR10 heterodimer functions in H. pylori lipopolysaccharide recognition. © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.
    Gastroenterology 04/2015; 148(4):S-118. DOI:10.1016/S0016-5085(15)30410-8 · 16.72 Impact Factor
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    ABSTRACT: Over the past 50 years, the prevalence of Helicobacter pylori infection has fallen as standards of living improved. The changes in the prevalence of infection and its manifestations (peptic ulcer disease and gastric mucosal lesions) were investigated in a large cohort of Sardinians undergoing upper endoscopy for dyspepsia. A retrospective observational study was conducted involving patients undergoing endoscopy for dyspepsia from 1995 to 2013. H. pylori status was assessed by histology plus the rapid urease test or 13C-UBT. Gastric mucosal lesions were evaluated histologically. Data including non-steroidal anti-inflammatory drugs (NSAIDs) use and the presence of peptic ulcers were collected. The prevalence of H. pylori was calculated for each quartile and for each birth cohort from 1910 to 2000. 11,202 records were retrieved for the analysis (62.9 % women). The overall prevalence of H. pylori infection was 43.8 % (M: 46.6 % vs. F: 42.0 %; P = 0.0001). A dramatic decrease in the prevalence of infection occurred over the 19-year observation period. The birth cohort effect was evident in each category (quartile) reflecting the continuous decline in H. pylori acquisition. Over time, the prevalence of peptic ulcers also declined, resulting in an increase in the proportion of H. pylori negative/NSAID positive and H. pylori negative/NSAID negative peptic ulcers. The prevalence of gastric mucosal changes also declined despite aging. The decline in H. pylori prevalence over time likely reflects the improvement in socioeconomic conditions in Sardinia such that H. pylori infection and its clinical outcomes including peptic ulcer are becoming less frequent even among dyspeptic patients.
    Internal and Emergency Medicine 03/2015; DOI:10.1007/s11739-015-1218-4 · 2.62 Impact Factor
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    David Y Graham ·
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    ABSTRACT: Most gastric cancers are caused by infection with the common human bacterial pathogen, Helicobacter pylori. It is now accepted that gastric cancer can be prevented and virtually eliminated by H. pylori eradication and this knowledge was responsible for country-wide H. pylori eradication combined with secondary cancer prevention for those with residual risk that was introduced in Japan in 2013. Korea is a high H. pylori prevalence and high gastric cancer incidence country and a good candidate for a gastric cancer elimination program. The presence of an H. pylori infection is now considered as an indication for treatment of the infection. However, antimicrobial drug resistance is common among H. pylori in Korea making effective therapy problematic. Country-wide studies of the local and regional antimicrobial resistance patterns are needed to choose the most appropriate therapies. H. pylori and gastric cancer eradication can be both efficient and cost effective making it possible and practical to make Korea H. pylori and gastric cancer free. There is no reason to delay.
    The Korean Journal of Internal Medicine 03/2015; 30(2):133-139. DOI:10.3904/kjim.2015.30.2.133 · 1.43 Impact Factor
  • Takahiro Uotani · David Y Graham ·
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    ABSTRACT: Helicobacter pylori (H. pylori) is a major human pathogen which causes progressive gastroduodenal damage. Guidelines recommend that, unless there are compelling reasons to delay, treatment is indicated for all patients in whom the infection is diagnosed. The rapid urease test (RUT) is a popular diagnostic test in that it is a rapid, cheap and simple test that detects the presence of urease in or on the gastric mucosa. The sensitivity and specificity are generally high and many versions have been approved for use in humans. Best results are obtained if biopsies are obtained from both the antrum and corpus. The tissue sample embedded in the RUT gel can also be utilized for other tests such as for molecular based tests of microbial susceptibility or for host factors. False-positive results are rare if the RUT contains an antibacterial agent to prevent growth of urease-containing contaminants and the tests are discarded at 24 hours. The use of antimicrobial drugs and proton pump inhibitors as well as the presence of intestinal metaplasia may result in false-negative results. A negative test should not be used as the criteria for cure or in cases where accuracy is important for patient management such as in upper gastrointestinal bleeding. Interpretation of the test should take into account the pretest probability and the prevalence of H. pylori in the population. The test can also be used to provide an informal assessment of the accuracy of the histopathology result and discrepancies should prompt a review of the histopathology and discussions with the pathologist.
    02/2015; 3(1):9. DOI:10.3978/j.issn.2305-5839.2014.12.04
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    ABSTRACT: The most recent information published on resistance of Helicobacter pylori to antibiotics in a large population in the United States is more than 10 y old. We assessed the susceptibility of H pylori to antibiotics among patients in a large metropolitan hospital, as well as demographic, clinical, and life-style factors associated with antimicrobial resistance. We performed a cross-sectional study at the Houston Veterans Affairs Medical Center of a random sample of 656 patients (90.2% men) from a cohort of 1559 undergoing esophagastroduodenoscopy with collection of gastric biopsies from 2009 through 2013. We performed culture analyses of gastric tissues to detect H pylori. The minimum inhibitory concentrations of amoxicillin, clarithromycin, metronidazole, levofloxacin, and tetracycline were determined by the Epsilometer test. Logistic regression analysis was performed to estimate the association between risk factors and antimicrobial resistance. Biopsies from 135 subjects (20.6%) tested positive for H pylori; 128 of these were from men (94.8%). Only 65 strains were susceptible to all 5 antibiotics. The prevalence of resistance to levofloxacin was 31.3% (95% confidence interval [CI], 23.1-39.4), to metronidazole was 20.3% (95% CI, 13.2-27.4), to clarithromycin was 16.4% (95% CI, 9.9-22.9), and to tetracycline was 0.8% (95% CI, 0.0-2.3). No isolate was resistant to amoxicillin. Clarithromycin resistance increased from 9.1% in 2009-2010 to 24.2% in 2011-2013. In multivariate analysis, prior treatment of H pylori infection and use of fluoroquinolones were significantly associated with clarithromycin and levofloxacin resistance, respectively. H pylori resistance to clarithromycin increased between 2009 and 2013; resistance to metronidazole remains high in infected men in the US. The high frequency of resistance to levofloxacin is a new and concerning finding. Copyright © 2015 AGA Institute. Published by Elsevier Inc. All rights reserved.
    Clinical Gastroenterology and Hepatology 02/2015; 13(9). DOI:10.1016/j.cgh.2015.02.005 · 7.90 Impact Factor

Publication Stats

20k Citations
4,651.75 Total Impact Points


  • 2005-2015
    • Michael E. DeBakey VA Medical Center
      • Center for Innovations in Quality, Effectiveness and Safety
      Houston, Texas, United States
    • University of Toronto
      Toronto, Ontario, Canada
  • 2000-2015
    • Università degli Studi di Sassari
      • Dipartimento di Scienze Biomediche
      Sassari, Sardinia, Italy
    • Houston Methodist Hospital
      Houston, Texas, United States
    • Prince of Wales Hospital, Hong Kong
      Chiu-lung, Kowloon City, Hong Kong
  • 1978-2015
    • Baylor College of Medicine
      • • Veterans Affairs Medical Center
      • • Department of Medicine
      Houston, Texas, United States
  • 1996-2014
    • United States Department of Veterans Affairs
      Bedford, Massachusetts, United States
  • 2013
    • Changi General Hospital
      • Department of Gastroenterology
      Tumasik, Singapore
  • 2007-2013
    • University of Padova
      Padua, Veneto, Italy
  • 1988-2012
    • Houston medical Center
      Ворнер Робинс, Georgia, United States
  • 2011
    • Oita University
      • Faculty of Medicine
      Ōita, Ōita, Japan
  • 2009
    • Marshall University
      Huntington, West Virginia, United States
  • 1990-2008
    • Spokane VA Medical Center
      Spokane, Washington, United States
  • 2006
    • Wakayama University
      Wakayama, Wakayama, Japan
  • 2001-2005
    • Shinshu University
      • Department of Clinical Laboratory Sciences
      Shonai, Nagano, Japan
    • American University Washington D.C.
      Washington, Washington, D.C., United States
  • 2004
    • Showa General Hospital
      Edo, Tōkyō, Japan
  • 2003
    • Kangbuk Samsung Hospital
      Sŏul, Seoul, South Korea
  • 1994-2003
    • Minneapolis Veterans Affairs Hospital
      Minneapolis, Minnesota, United States
  • 2002
    • Duke University
      Durham, North Carolina, United States
  • 2001-2002
    • University of Pittsburgh
      Pittsburgh, Pennsylvania, United States
  • 1997
    • Université Libre de Bruxelles
      Bruxelles, Brussels Capital Region, Belgium
    • Otto-von-Guericke-Universität Magdeburg
      • Clinic for Gastroenterology, Hepatology and Infectiology
      Magdeburg, Saxony-Anhalt, Germany
  • 1983-1994
    • Texas Medical Center
      Houston, Texas, United States
  • 1988-1989
    • Houston Zoo
      Houston, Texas, United States