, for their stimulating discussions, lots of laughter and some much needed day to day support. I owe my deepest gratitude to them for celebrating my birthday all these years. Thanks buddies, keep up the good work! I am thankful to Dr Ke Jingxia for working late with me in the laboratory during my first two years of study and listening to my frustrations when my experiments were failed. Special thanks go to my colleague cum concert buddy, Shu Harn, for her interesting discussions not only about research, but also about wonderful music and opera. Who says Ph.D. is boring with just experiments! I am also grateful to her for helping me with the statistical analysis. Special thanks go to NTU which provides me state-of-the-art research facilities and a teaching assistantship for my second year of study. I thank technical staffs in the Environment Laboratory, especially Aidil Bin Md Idris for his assistance with water sample collection and transportation. I convey special acknowledgement to Melissa Chong for her indispensable help dealing with laboratory matters and research accounts. I am thankful to Ng Soo Ching from the graduate office for her kind help of the administration matters. I would like to acknowledge Public Utilities Board (PUB), Singapore, for providing research grant and scholarship for my Ph.D. program. I owe my profound gratitude to Dr. Lynette Oon Lin Ean and Dr. Eileen Chen Xueqin from the Department of Pathology, Singapore General Hospital for their collaboration in norovirus diagnostic during gastroenteritis outbreaks. Special thanks also go to Professor Albert Bosch from the University of Barcelona for providing astrovirus strain and DSO National Laboratories for providing norovirus plasmids.