The main purpose of surveillance in public health is to monitor disease trends. It involves the systematic collection, analysis, and interpretation of health data to identify outbreaks, track the spread of diseases, and evaluate the effectiveness of interventions. This process enables timely public health responses and informed decision-making to control and prevent further disease transmission. Surveillance is not designed for treating individual patients or reducing costs directly but focuses on population-level health monitoring.

Reference: Principles of Epidemiology, Rose, Edition 3.