Changing patterns of infectious diseases.

In the 20 years that have passed since I received my medical degree, some of the most evident, striking, and interesting changes in patterns of diseases have occurred among those due to transmissible agents. Among other changes are the recognition of new diseases, new clinical manifestations for old diseases, new ecologic niches for traditional pathogens, and new modes of disease transmission. Implicated causes for these changes include alterations in lifestyle such as sexual behaviour, leisure activity, and dietary trends, along with the impact of immigration and the effects of medical progress. A review of these changing patterns demonstrates the dynamic nature of medicine and suggests lessons for medical education.