Masahiro Asaka,
Third Department of Internal Medicine, Hokkaido University School of Medicine,
Sapporo 0608638, Japan
(Tel: 81-11-716-1161 Fax: 81-11-706-7867 E-mail: maasaka@med.hokudai.ac.jp)
Helicobacter pylori (H. pylori) infection causes histological gastritis, and chronic gastritis due to long-term H. pylori infection results in gastric mucosal atrophy, which eventually progresses to intestinal metaplasia and sometimes to gastric cancer. In Japan, it has become apparent that chronic infection with H. pylori causes atrophic gastritis in 80% or more of infected persons by the age of 50 years and that intestinal metaplasia develops in about 50% of this group. Gastric cancer, particularly intestinal type of gastric cancer, is generally considered to arise via gastric mucosal atrophy and intestinal metaplasia. According to data published by the WHO (1997), the cummulative incidence of gastric cancer between the ages of 0 and 75 was 6.5% in Japan. On the basis of these data and stratification by the presence or absence of H. pylori infection, the cumulative incidence of gastric cancer was 11.2% and 1.8% in H. pylori-positive and -negative individuals, respectively. Therefore, just over 10% of H. pylori-infected persons in Japan may develop gastric cancer throughout their lives.
The prevalence of asymptomatic H. pylori infection differs greatly among countries, being low in developed countries and high in developing countries. This tendency has been shown to be more marked in the younger age groups. H. pylori is transmitted via the fecal-oral route and children are apparently more readily infected than adults. Thus, it should be realized that conducting a survey on H. pylori infection is the same as assessing the water supply and sewerage systems of a country. The prevalence of H. pylori infection in Japan is extremely low at an early age, as in other developed countries, and subsequently shows a rapid increase until it reaches a plateau of about 70% at 50 years of age. This phenomenon is thought to occur because people about 50 years old were born soon after World War II and spent their childhood in conditions of poor hygiene.
The incidence of gastric cancer also varies among countries. According to the 1995 data reported by the WHO, the number of deaths from gastric cancer per 100,000 men was 51 in Japan, which was very high compared with Western countries. However, of 60 million persons who infected with H. pylori in Japan, only 235,000 had gastric cancer in 1993 (only 0.4% of the infected group). It is suggested that H. pylori infection leads to histological chronic gastritis regardless of the strain of this organism, and after that the course of the disease does depend on the environmental factors such as diet, duration of or age at H. pylori infection, the virulence of H. pylori strains, and host factors including genetic make-up.
Masahiro Asaka, M.D., Ph.D. Medical School Education:
March, 1972 Finished Hokkaido University School of Medicine; Received Degree of M.D.
March, 1979 Received Degree of Ph. D.
Teaching or Research Experience:
1972-1978 Resident, Hokkaido University Hospital
1978-1983 Instructor of Third Department of Internal Medicine, Hokkaido University, School of Medicine
1983-1994 Assistant Professor of Third Department of Internal Medicine, Hokkaido University, School of Medicine
1994-Present Chairman and Professor of Third Department of Internal Medicine, Hokkaido University, School of Medicine, Head of Gastroenterology and Hematology Section