Dr Au is a specialist in Public Health Medicine. He has served in various areas of public health in the Department of Health (DH) since 2003.

From 2023 to 2024, he was Head of the Emergency Response and Programme Management Branch of Centre for Health Protection (CHP) of DH, responsible for developing contingency plans, coordinating drills and exercises to enhance public health crisis preparedness and response mechanisms, and overseeing the planning, implementation, and enhancement of various vaccination programmes.

Currently, Dr Au serves as Head of the Communicable Disease Branch of CHP. He oversees communicable disease surveillance, epidemiological investigations of infectious disease outbreaks, enforcement of the Prevention and Control of Disease Ordinance (Cap. 599) and the International Health Regulations, and implementation of other related public health measures. He is also an ex-officio member of the Scientific Committee on Emerging and Zoonotic Diseases of the CHP.