A large-scale<unk>  shows scale-free property. The degree distribution follows a power law suggesting that only a few diseases connect to a large number of diseases, whereas most diseases have few links to others. Such network also shows a clustering tendency by disease classes. In a symptom-based disease network, disease are also clustered according to their categories. Moreover, diseases sharing the same symptom are more likely to share the same genes and protein interactions.
Human disease network
Phenotypic disease network 
Disease registry
Enterprise master patient index
Public health surveillance
Hazardous Substances Data Bank
Cognitive epidemiology
Nutritional rating systems