Studies on the number of Helicobacter pylori-infected individuals and prevalence rate of infection
| First author | No of subjects | Population | Study design | Observation year |
| Asaka27 | 426 | Asymptomatic children, students and adults (participating at the health screening centre) living in Sapporo, Hokkaido | Observational study | 1990 |
| Fujisawa31 | 349 | Healthy persons living in seven prefectures in the central part of Japan | Observational study | 1974 |
| 324 | 1984 | |||
| 342 | 1994 | |||
| Watabe32 | 6 983 | Participants in a mass health appraisal programme | Observational study | 1996 |
| Ueda33 | 14 716 | Individuals who underwent a health check-up in seven prefectures (Hokkaido, Aomori, Yamagata, Gunma, Aichi, Shiga and Kagawa) | Observational study | 2005 |
| Shiota34 | 5 550 | Patients of Oita University Hospital, Oita, Japan | Observational study | 2009 |