Abstract
Public health surveillance is the ongoing collection, analysis, and dissemination of health related data to provide information that can be used to monitor and improve the health of populations. Such surveillance systems can be established in many settings to study a variety of populations and conditions. The most effective systems are designed around specific, well-defined objectives, collect data in a standardized fashion, analyze the data frequently, and disseminate the results to those who need to know the information. Surveillance has been used to determine the occurrence rates of hemophilia and to characterize the population affected by this rare but potentially serious congenital disorder. Data from surveillance systems have been used to identify risk factors for complications that, once identified, have been modified through public health interventions. The effectiveness of these interventions can be assessed by continued surveillance, thereby assuring improvement in care of people affected by hemophilia around the world.