CHILILAB DSS is a field laboratory attached to the Hanoi School of Public Health in Vietnam. It is located in Chi Linh district of Hai Duong province in the northern part of Vietnam and is about 60 km northeast of Hanoi. The population base for this surveillance system is approximately 56,000 inhabitants who live in 3 townships and 4 communes across a land area of 137.5 square kilometers which are under rapid process of urbanization. Adolescents and young adults aged between 15-24 years account for approximately 20% of the total district population.