Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, Taipei, Taiwan. Taiwan Centers for Disease Control, Taipei, Taiwan. Department of Laboratory Medicine, Linkou Chang Gung Memorial Hospital, Taoyuan, Taiwan. Department of Medical Biotechnology and Laboratory Science, Chang Gung University, Taoyuan, Taiwan. Center for Drug Evaluation, Taipei, Taiwan. Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, Taipei, Taiwan. fangct@ntu.edu.tw. Division of Infectious Diseases, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan. fangct@ntu.edu.tw.