Advance Publication. Journal of Atherosclerosis and Thrombosis

Transcription

1 1 Original Article Helicobacter Pylori Infection and Risk of Death From Cardiovascular Disease Among the Japanese Population: a Nested Case-Control Study within the JACC Study Yingsong Lin 1, Yuki Obata 2, Shogo Kikuchi 1, Akiko Tamakoshi 3 and Hiroyuki Iso 4 for the JACC Study Group 1 Department of Public Health, Aichi Medical University School of Medicine, Nagakute, Aichi, Japan 2 Department of Pharmacy, Kinjo Gakuin University, Nagoya, Japan 3 Department of Public Health, Hokkaido University Graduate School of Medicine, Sapporo, Japan 4 Department of Social and Environmental Medicine, Osaka University Graduate School of Medicine, Suita, Osaka, Japan Aim: An increasing number of studies have linked Helicobacter pylori (H. pylori) infection to extragastric diseases; however, the role of H. pylori in the pathogenesis of cardiovascular disease (CVD) remains controversial. We examined the association between H. pylori infection and risk of death from coronary heart disease (CHD) and stroke in a nested case-control study within a large prospective cohort study of Japanese subjects. Methods: The cases were 627 subjects who died from CHD and stroke during the follow-up period until December 31, 2003, and 627 control subjects were selected and matched to cases on sex, age, and area. Commercial immunoassay IgG enzyme-linked immunosorbent assay kits were used for the determination of the seropositivity for H. pylori. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using a conditional logistic regression model. Results: Overall, H. pylori infection was not associated with CVD (CHD and stroke) mortality risk. The multivariable OR was 0.96 ( ) for the H. pylori positive subjects in comparison with H. pylori negative subjects. As for the subtype of CVD, H. pylori appears to be inversely associated with the risk of death from CHD, with an OR of 0.79 ( ), but this was not statistically significant. No significant association was observed between H. pylori infection and stroke, with an OR of 1.02 ( ). Conclusion: The results of this nested case-control study suggest that there is no association between H. pylori infection and CHD and stroke mortality risk in otherwise healthy, elderly Japanese individuals. J Atheroscler Thromb, 2015; 22: Key words: Helicobacter pylori, Cardiovascular disease, Nested case-control study Introduction Helicobacter pylori (H. pylori) colonizes the human stomach, often causing gastritis and peptic ulcers 1). There is also convincing evidence that H. pylori infection is causally related to gastric cancer 2). An increasing number of studies have linked H. pylori infection Address for correspondence: Shogo Kikuchi, Department of Public Health, Aichi Medical University School of Medicine, 1-1 Yazakokarimata, Nagakute, Aichi , Japan kikuchis@aichi-med-u.ac.jp Received: September 16, 2014 to extragastric diseases, including iron deficiency anemia, idiopathic thrombocytopenic purpura, and cardiovascular disease (CVD) 3). The positive association of H. pylori infection with CVD was first reported in a case-control study 4) in which individuals with H. pylori seropositivity had an increased risk, approximately two-fold, of developing CVD. However, not all subsequent studies have supported these results 5-13). For example, a 1998 meta-analysis of 18 studies found no significant association between H. pylori and risk of coronary heart disease (CHD), a major component of CVD 14). Furthermore, neither of the two recent cohort studies showed a significant, positive associa-

2 2 Statistical Analysis The sample size was estimated based on the following assumptions: odds ratio 2, H. pylori seropositivity among control subjects 75%, alpha 5%, power 80%, and case/control ratio 1. Under the above consumptions, 212 cases and 212 controls are needed. Our study had a sufficient sample size to detect statistically significant associations. Characteristics between cases and controls were compared using the Mann Whitney tests for continuous variables and chi-square tests for discrete variables. Conditional logistic regression models were used to estimate crude and multivariable-adjusted odds ratios (OR) and 95% confidence intervals (CI) for CHD or stroke death in relation between these outcome measures 12, 13). Although the role of H. pylori in the pathogenesis of CVD remains controversial, the proposed mechanism of action, i.e., the changes in inflammatory markers in H. pylori positive individuals may be associated with increased risk of CVD, persists 15). The prevalence of H. pylori infection is approximately 50% among Japanese adults aged over 50 years, though a decreasing trend has been observed in various age groups 16). To our knowledge, only one prospective, nested case-control study has examined the relationship between H. pylori infection and risk of myocardial infarction and stroke in Japanese subjects 17), which found no significant associations. Given that CVD is the second leading cause of death in Japan, it would be highly beneficial to identify any novel, significant risk factors whereby avoidance may help to reduce overall CVD risk. Thus, we have prospectively examined the association between H. pylori infection and risk of death from CVD in an attempt to identify such a risk factor. Methods Study Population We conducted a nested case-control study within the Japanese Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study), a large, prospective study that investigated potential associations between various lifestyle factors and various outcome measures including cancer and CVD mortality 18). From 1988 to 1990, we recruited 110,585 people aged years from 45 locations throughout Japan. At baseline, participants completed a self-administered questionnaire covering demographic characteristics, medical history, and lifestyle factors, and approximately 35% of the participants provided a blood sample. Information on hypertension and diabetes was based on self-report. For alcohol drinking, the cohort participants were asked to describe the drinking status, frequency, and amount. No significant differences were noted in characteristics, such as age, body mass index (BMI), location, education level, and medical history, between those who donated the blood sample and those who did not. The sera were separated from these samples as quickly as possible after blood withdrawal and then stored at 80 until analysis. The causes of death were noted from the death certificates and classified according to the International Classification of Diseases, tenth revision (ICD-10). The codes were I20-I25 for CHD and I60-69 for stroke. Of the 27,410 deaths from all the causes documented during the follow-up period of the JACC Study, 4287 men and 4043 women died from CVD (18). For our nested case-control study, the cases that were selected met the criteria of having provided a baseline blood sample and having died from CHD and stroke, as determined by the JACC Study, during the follow-up until December 31, ). Those who were identified in the JACC Study as being diseasefree at the time the study ended were then selected from the remaining participants as controls 18). The controls were matched with the cases in terms of sex, age, and area at a ratio of 1:1. The cohort participants were excluded if they reported a history of stroke or myocardial infarction at baseline. As a result, 627 cases and 627 control subjects were included in the present study. Measurement of Metabolic Profiles Blood pressure was measured using a mercury sphygmomanometer. Serum total and high-density lipoprotein (HDL) cholesterol was measured using the enzymatic method with an automatic analyzer (Hitachi , Hitachi Medical Corp., Tokyo, Japan). Two commercial immunoassay IgG enzyme-linked immunosorbent assay (ELISA) kits were used for determining the seropositivity for H. pylori. J-HM-CAP (Kyowa Medex, Japan) was used for cases who died before 1998, as well as their matched controls, whereas for cases who died between 1998 and 2003, and their controls, E-Plate (Eiken Inc., Tokyo) was used because of the termination of J-HM-CAP production. Assays were performed according to the manufacturer s instructions and seropositivity was defined using recommended cutoff values. Both ELISA kits used antigens derived from Japanese H. pylori strains and have been shown to perform better than other commercial ELISA kits 19, 20). All laboratory tests were conducted at the laboratory of the Department of Public Health, Aichi Medical University School of Medicine, with staff blinded to the case-control status.

3 Table 1. Characteristics of cases and controls Characteristics Sex Men Women Age, y Body mass index, kg/m 2 History of hypertension, % History of diabetes, % Smoking status, % Non-smokers Ex-smokers Current smokers Drinking status, % Non-drinkers Ex-drinkers Current drinkers Systolic blood pressure, mmhg Diastolic blood pressure, mghg Total cholesterol, mg/dl High density lipoprotein cholesterol, mg/dl Helicobacter pylori seropositivity, % Plus minus values are mean standard deviation The percentages do not add up to 100% due to missing values. 3 Cases (n 627) Controls (n 627) p values Matching factor Matching factor tion to H. pylori seropositivity. The multivariate analyses were adjusted for BMI (continuous), cigarette smoking (never, ex, current), alcohol consumption (never, ex, current), and systolic blood pressure (SBP, continuous). The selection of covariates included in the model was based on the results from univariate analyses and testing of multicollinearity. A history of diabetes and serum total and HDL cholesterol were not included in the model because the risk estimates remained unchanged after additional adjustment for these two factors. All statistical tests were two-sided and a P value less than 0.05 was used to indicate statistical significance. All analyses were performed using SAS Release 9.1 (SAS Institute Inc., Cary, NC). Results Table 1 outlines the characteristics of cases and controls. The cases were more likely to have a history of hypertension and to be a current smoker, in comparison with controls. The cases were less likely to have a history of diabetes when compared with controls. Mean SBP and DBP was lower in cases than that in controls, and the mean total cholesterol was higher in cases than that in controls. Importantly, the preva- lence of H. pylori seropositivity was comparable between cases and controls, 75.9% and 76.4%, respectively. Table 2 summarizes the associations between H. pylori infection and risk of death from CHD and stroke. Overall, the multivariable OR was 0.96 ( ) for H. pylori-positive subjects compared with H. pylori-negative subjects, after adjustment for potential confounding factors. H. pylori was inversely associated with the risk of death from CHD (OR, 0.79; 95% CI, ). However, the association was not statistically significant. Similarly, no significant association was observed between H. pylori infection and stroke (OR, 1.02; 95% CI, ). Discussion To date, there is insufficient evidence on the association between H. pylori infection and CVD risk in Asian countries. Our results suggest that H. pylori is not significantly associated with the risk of death from CHD or stroke within a Japanese population group. The majority of previous research on the above association was conducted in Western countries 5-13) and findings have been inconsistent and inconclusive. It is possible, however, that variations in the study

4 4 Table 2. The association between H. pylori infection and CVD mortality risk CVD (CHD stroke) Case/Control Crude OR (95%CI) Multivariate OR (95%CI) CHD (I20 25) Case/Control Crude OR (95%CI) Multivariate OR (95%CI) Stroke (I60 69) Case/Control Crude OR (95%CI) Multivariate OR (95%CI) Negative 151/148 40/34 111/114 Seropositivity Positive 476/ ( ) 0.96 ( ) 139/ ( ) 0.79 ( ) 337/ ( ) 1.02 ( ) OR: odds ratio; CI: confidence interval; CVD: cardiovascular disease; CHD: coronary heart disease OR and CI were estimated from conditional logistic regression models Multivariate OR: adjusted for body mass index, cigarette smoking, alcohol drinking, and systolic blood pressure. The outcome was CHD and stroke mortality tions amongst differing populations. In addition to sample size and adjustment for confounders, another possible contributing factor is differing measuring equipment across studies. The effect of measurement kits on the results should be considered because the validity of serologic tests may vary depending on the type of antigens used in ELISA kits. Although both ELISA kits in this study used the antigen derived from Japanese subjects and have been shown to perform better when compared with other commercial ELISA kits, data were lacking on the direct comparison of performance for the ELISA kits used. Because separate analyses for subjects measured using either J-HM- CAP or E-Plate ELISA kits showed similar results, we chose to combine data sets derived from the two ELISA tests. Of multiple mechanisms proposed to explain the H. pylori infection CVD associations 15, 22), the effect of H. pylori colonization on atherosclerosis through the generation of a persistent low-grade inflammatory stimulus is plausible. This is because previous studies provided indirect evidence that serum lipid or inflammatory biomarkers such as CRP were significantly higher in H. pylori infected individuals compared with H. pylori-negative individuals 23-25). Furthermore, H. pylori was significantly associated with metabolic syndrome in a cross-sectional study involving approximately 7400 Japanese subjects 26). We compared several CVD risk factor profiles between H. pylori-positive and H. pylori-negative individuals among control submethodology and the adjustment for potential confounders has contributed to inconsistent results in the literature. For example, the majority of studies showing a positive association are case-control or cross-sectional studies. However, these studies may have been limited by a small sample size and lack appropriate adjustment for potential confounders. In contrast, the findings from several prospective studies involving a large sample size showed no or only modest association between H. pylori infection and overall CVD mortality 11-13). Although a review of evidence till date does not support the major role of H. pylori in the development of CVD, it is possible that H. pylori, especially specific CagA positive H. pylori strains, is associated with the risk of certain subtypes of stroke or CHD 7). A prospective analysis of data from the National Health and Nutrition Examination Survey III showed an inverse association between H. pylori and stroke mortality, with a hazard ratio of 0.69 ( ) for individuals infected with H. pylori 13). A case-control study found that chronic H. pylori infection was significantly associated with increased risk of ischemic stroke in Japanese, with an OR of 2.57 ( ) for all subtypes combined 21). In contrast, our nested case-control study did not show any significant associations between H. pylori and subtypes of stroke, including subarachnoid hemorrhage, cerebral hemorrhage, and cerebral infarction (data not shown). Further studies are required to clarify the underlying mechanisms of varied associa-

5 jects, and found no significant differences in blood pressure, history of diabetes, serum total, or HDL cholesterol levels between the two groups (data not shown). The differences in sample size and measurement methods may partly account for the inconsistent findings on the metabolic profiles related to H. pylori infection. Strengths of this study include its prospective design, a relatively large sample size, and the ability to adjust for potential confounders such as smoking, alcohol consumption, and risk factors for CVD that had already been identified. In contrast, there were several limitations to the study. Firstly, one concern is that using death certificates may lead to the misclassification in the causes of deaths. Unfortunately, incidence data on CVD were unavailable for the present analysis. Secondly, we did not have data on CagA status, which is an important virulence factor for H. pylori. This is relevant because previous studies involving populations of European ancestry have suggested a positive association among individuals with CagApositive-H. pylori strains and atherosclerosis 7, 27). However, we believe that this issue may not be a concern because the majority of H. pylori strains were CagApositive in East Asian populations, including those of Japan 28). Thirdly, the data were lacking on the eradication therapy for H. pylori. The risk estimates might have been biased if case and control subjects had a different proportion of eradication therapy. Finally, although we adjusted for known CVD risk factors, we could not rule out the possibility that other confounders such as exercise and socioeconomic status may have influenced these estimates. Exercise data were unavailable for the present analysis. For socioeconomic status, prior research has consistently demonstrated that a lower socio-economic status and/or a low level of education is associated with an increased prevalence of H. pylori infection 29). In conclusion, the results of this study indicate no association between H. pylori infection and CVD (CHD and stroke) mortality risk in otherwise healthy, elderly Japanese individuals. Given the complex role of H. pylori in health and disease, this association needs to be further investigated through additional prospective studies in Asian countries that have a high prevalence of H. pylori infection. Acknowledgments This work was supported by a Grant-in-Aid for Scientific Research (B) (no ) from the Japanese Ministry of Education, Culture, Sports, Science and Technology. The JACC Study was supported by 5 Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan (Monbusho), Grants-in-Aid for Scientific Research on Priority Areas of Cancer, as well as Grants-in-Aid for Scientific Research on Priority Areas of Cancer Epidemiology from the Japanese Ministry of Education, Culture, Sports, Science and Technology (Monbu- Kagaku-sho) (Nos , , , , , , , , , , , , , , and ). We express our appreciation to Drs. Kunio Aoki and Yoshiyuki Ohno, Professors Emeritus of the Nagoya University School of Medicine and former chairpersons of the JACC Study. We are also greatly indebted to Dr. Haruo Sugano, former Director of the Cancer Institute, Tokyo, who greatly contributed to the initiation of the JACC Study, Dr. Tomoyuki Kitagawa, Director Emeritus of the Cancer Institute of the Japanese Foundation for Cancer Research and former chairman of the Grant-in-Aid for Scientific Research on Priority Area Cancer and to Dr. Kazao Tajima, Aichi Cancer Center and previous chairman of the Grant-in Aid for Scientific Research on Priority Area of Cancer Epidemiology, for their warm encouragement and support of this study. The present members of the JACC Study Group who co-authored this paper are: Dr. Akiko Tamakoshi (present chairperson of the study group), Hokkaido University Graduate School of Medicine; Drs. Mitsuru Mori & Fumio Sakauchi, Sapporo Medical University School of Medicine; Dr. Yoshihiro Kaneko, Akita University School of Medicine; Dr. Ichiro Tsuji, Tohoku University Graduate School of Medicine; Dr. Yosikazu Nakamura, Jichi Medical School; Dr. Hiroyasu Iso, Osaka University School of Medicine; Dr. Haruo Mikami, Chiba Cancer Center; Dr. Michiko Kurosawa, Juntendo University School of Medicine; Dr. Yoshiharu Hoshiyama, Yokohama Soei University; Dr. Naohito Tanabe, University of Niigata Prefecture; Dr. Koji Tamakoshi, Nagoya University Graduate School of Health Science; Dr. Kenji Wakai, Nagoya University Graduate School of Medicine; Dr. Shinkan Tokudome, National Institute of Health and Nutrition; Dr. Koji Suzuki, Fujita Health University School of Health Sciences; Dr. Shuji Hashimoto, Fujita Health University School of Medicine; Dr. Shogo Kikuchi, Aichi Medical University School of Medicine; Dr. Yasuhiko Wada, Faculty of Nutrition, University of Kochi; Dr. Takashi Kawamura, Kyoto University Center for Student Health; Dr. Yoshiyuki Watanabe, Kyoto Prefectural University of Medicine Graduate School of Medical Science; Dr. Kotaro Ozasa, Radiation Effects Research

6 6 Foundation; Dr. Tsuneharu Miki, Kyoto Prefectural University of Medicine Graduate School of Medical Science; Dr. Chigusa Date, School of Human Science and Environment, University of Hyogo; Dr. Kiyomi Sakata, Iwate Medical University; Dr. Yoichi Kurozawa, Tottori University Faculty of Medicine; Drs. Takesumi Yoshimura & Yoshihisa Fujino, University of Occupational and Environmental Health; Dr. Akira Shibata, Kurume University; Dr. Naoyuki Okamoto, Kanagawa Cancer Center; and Dr. Hideo Shio, Moriyama Municipal Hospital. Conflicts of Interest The authors have no financial relationship to disclose. References 1) McColl KE: Helicobacter pylori infection. New Engl J Med, 2010; 362: ) Peek RM Jr, Blaser MJ: Helicobacter pylori and gastrointestinal tract adenocarcinomas. Nat Rev Cancer, 2002; 2: ) Tan HJ, Goh KL: Extragastrointestinal manifestations of Helicobacter pylori infection: facts or myth? A critical review. J Dig Dis, 2012; 13: ) Mendall MA, Goggin PM, Molineaux N, Levy J, Toosy T, Strachan D, Camm AJ, Northfield TC: Relation of Helicobacter pylori infection and coronary heart disease. Br Heart J, 1994; 71: ) Patel P, Mendall MA, Carrington D, Strachan DP, Leatham E, Molineaux N, Levy J, Blakeston C, Seymour CA, Camm AJ: Association of Helicobacter pylori and Chlamydia pneumoniae infections with coronary heart disease and cardiovascular risk factors. BMJ, 1995; 311: ) Franceschi F, Leo D, Fini L, Santoliquido A, Flore R, Tondi P, Roccarina D, Nista EC, Cazzato AI, Lupascu A, Pola P, Silveri NG, Gasbarrini G, Gasbarrini A: Helicobacter pylori infection and ischaemic heart disease: an overview of the general literature. Dig Liver Dis, 2005; 37: ) Franceschi F, Niccoli G, Ferrante G, Gasbarrini A, Baldi A, Candelli M, Feroce F, Saulnier N, Conte M, Roccarina D, Lanza GA, Gasbarrini G, Gentiloni SN, Crea F: CagA antigen of Helicobacter pylori and coronary instability: insight from a clinico-pathological study and a meta-analysis of 4241 cases. Atherosclerosis, 2009; 202: ) Longo-Mbenza B, Nsenga JN, Mokondjimobe E, Gombet T, Assori IN, Ibara JR, Ellenga-Mbolla B, Vangu DN, Fuele SM: Helicobacter pylori infection is identified as a cardiovascular risk factor in Central Africans. Vasc Health Risk Manag, 2012; 6: ) Heuschmann PU, Neureiter D, Gesslein M, Craiovan B, Maass M, Faller G, Beck G, Neundoerfer B, Kolominsky- Rabas PL: Association between infection with Helico- bacter pylori and Chlamydia pneumoniae and risk of ischemic stroke subtypes: Results from a population-based case-control study. Stroke, 2001; 32: ) Wald NJ, Law MR, Morris JK, Bagnall AM: Helicobacter pylori infection and mortality from ischaemic heart disease: negative result from a large, prospective study. BMJ, 1997; 315: ) Haider AW, Wilson PW, Larson MG, Evans JC, Michelson EL, Wolf PA, O Donnell CJ, Levy D: The association of seropositivity to Helicobacter pylori, Chlamydia pneumoniae, and cytomegalovirus with risk of cardiovascular disease: a prospective study. J Am Coll Cardiol, 2002; 40: ) Schöttker B, Adamu MA, Weck MN, Müller H, Brenner H: Helicobacter pylori infection, chronic atrophic gastritis and major cardiovascular events: a population-based cohort study. Atherosclerosis, 2012; 220: ) Chen Y, Segers S, Blaser MJ: Association between Helicobacter pylori and mortality in the NHANES III study. Gut, 2013; 62: ) Danesh J, Peto R: Risk factors for coronary heart disease and infection with Helicobacter pylori: meta-analysis of 18 studies. BMJ, 1998; 316: ) Fong IW: Emerging relations between infectious diseases and coronary artery disease and atherosclerosis. CMAJ, 2000; 163: ) Ueda J, Gosho M, Inui Y, Matsuda T, Sakakibara M, Mabe K, Nakajima S, Shimoyama T, Yasuda M, Kawai T, Murakami K, Kamada T, Mizuno M, Kikuchi S, Lin Y, Kato M: Prevalence of Helicobacter pylori infection by birth year and geographic area in Japan. Helicobacter, 2014; 19: ) Ikeda A, Iso H, Sasazuki S, Inoue M, Tsugane S, JPHC Study Group: The combination of Helicobacter pyloriand cytotoxin-associated gene-a seropositivity in relation to the risk of myocardial infarction in middle-aged Japanese: The Japan Public Health Center-based study. Atherosclerosis, 2013; 230: ) Tamakoshi A, Ozasa K, Fujino Y, Suzuki K, Sakata K, Mori M, Kikuchi S, Iso H: Cohort Profile of the Japan Collaborative Cohort Study at Final Follow-up. J Epidemiol, 2013; 23: ) Obata Y, Kikuchi S, Miwa H, Yagyu K, Lin Y, Ogihara A: Diagnostic accuracy of serological kits for Helicobacter pylori infection with the same assay system but different antigens in a Japanese patient population. J Med Microbiol, 2003; 52: ) Matsuo K, Hamajima N, Suzuki T, Nakamura T, Matsuura A, Tominaga S: Better ROC curves for a regionally developed Helicobacter pylori antibody test. Asian Pac J Cancer Prev, 2001; 2: ) Sawayama Y, Ariyama I, Hamada M, Otaguro S, Machi T, Taira Y, Hayashi J: Association between chronic Helicobacter pylori infection and acute ischemic stroke: Fukuoka Harasanshin Atherosclerosis Trial (FHAT). Atherosclerosis, 2005; 178: ) He C, Yang Z, Lu NH: Helicobacter pylori-an infectious risk factor for atherosclerosis? J Atheroscler Thromb, 2014; 21: ) Ishida Y, Suzuki K, Taki K, Niwa T, Kurotsuchi S, Ando

7 H, Iwase A, Nishio K, Wakai K, Ito Y, Hamajima N: Significant association between Helicobacter pylori infection and serum C-reactive protein. Int J Med Sci, 2008; 5: ) Sung KC, Rhee EJ, Ryu SH, Beck SH: Prevalence of Helicobacter pylori infection and its association with cardiovascular risk factors in Korean adults. Int J Cardiol, 2005; 102: ) Satoh H: On lipid profile and Helicobacter pylori infection. J Atheroscler Thromb, 2011; 18: ) Gunji T, Matsuhashi N, Sato H, Fujibayashi K, Okumura M, Sasabe N, Urabe A: Helicobacter pylori infection is significantly associated with metabolic syndrome in the Japanese population. Am J Gastroenterol, 2008; 103: ) Mayr M, Kiechl S, Mendall MA, Willeit J, Wick G, Xu Q: Increased risk of atherosclerosis is confined to CagApositive Helicobacter pylori strains: prospective results from the Bruneck study. Stroke, 2003; 34: ) Yamaoka Y, Kodama T, Kita M, Imanishi J, Kashima K, Graham DY: Relationship of vaca genotypes of Helicobacter pylori to caga status, cytotoxin production, and clinical outcome. Helicobacter, 1998; 3: ) Veldhuyzen van Zanten SJ: Do socio-economic status, marital status and occupation influence the prevalence of Helicobacter pylori infection? Aliment Pharmacol Ther, 1995; 9 Suppl 2: 41-44