1. 1 Department of Community Medicine, Faculty of Medical Sciences , University of Fukui , Fukui , Japan
2. 2 Department of Infectious Diseases, Faculty of Medical Sciences , University of Fukui , Fukui , Japan
3. 3 Department of Biostatistics, Faculty of Medical Science , University of Fukui , Fukui , Japan
4. 4 Department of Health and Welfare , Fukui Prefecture , Fukui , Japan
5. 5 Department of Infection Prevention and Control , University of Fukui Hospital , Fukui , Japan