Abstract:
Disease and illness are not synonymous. In most instances, disease is demonstrable by anatomic, physiologic, biochemical, microbiologic, or immunologic abnormalities. Disease is a pathologic process. Not all persons with a disease are sick or ill. Symptoms of illness associated with a disease may be manifest or persist after the disease has disappeared.
The absence of demonstrable disease, however, does not necessarily mean that symptoms of illness are unreal. Recovery from disease and recovery from illness are not always equated. Many factors, including personal characteristics and social circumstances, can be responsible for recovery from disease and illness.
Chronic fatigue syndrome or symptoms of illness can persist in some patients but not in others after many different diseases.
Source: Cluff LE. Medical aspects of delayed convalescence. Rev Infect Dis. 1991 Jan-Feb;13 Suppl 1:S138-40. http://www.ncbi.nlm.nih.gov/pubmed/2020799