Final answer:
Emerging infectious diseases can appear for the first time, or re-emerge with increasing incidence or range, and do not always involve sporadic cases in endemic areas. They can lead to epidemics or pandemics and are distinct from sporadic and endemic diseases, which have different patterns of occurrence.
Step-by-step explanation:
The statement 'All of the following are true concerning emerging infectious diseases EXCEPT they always involve sporadic cases in endemic areas' is not accurate. Emerging infectious diseases can be defined as diseases that are newly appearing in a population, or have existed before but are rapidly increasing in incidence or geographic range. This includes diseases that may become more prevalent due to changes in the environment, the pathogen, or the host population.
Sporadic diseases are seen only occasionally and usually without geographic concentration, such as tetanus or rabies. In contrast, endemic diseases are always present at a certain level of incidence within a geographical area, like malaria in tropical regions. Therefore, emerging diseases do not always involve sporadic cases in endemic areas as they may also result in outbreaks, epidemics, or pandemics, significantly exceeding what is expected in endemic situations.
An epidemic is a large-scale outbreak of an infectious disease that isn't always present in a population, like the flu during specific seasons. Similarly, some diseases can be dormant and re-emerge more virulently than before, or were under control until resurging due to changes in population immunity or other factors. An example is tuberculosis, which has seen a resurgence in densely populated urban areas.