Which of the following best describes an ‘epidemic’?

An epidemic is best described as a sudden increase in disease cases that exceeds what is normally expected in a particular area. This definition highlights the element of unexpectedness and signifies that the number of cases has surged beyond the baseline or usual occurrence of that disease. The focus on the term "sudden increase" indicates that an epidemic is characterized not just by a high number of cases, but by a rise that is remarkable when compared to the previously established patterns for that disease in the population.

The other definitions do not encapsulate the full meaning of an epidemic. The idea of an unexpected increase in disease across the world suggests a pandemic rather than an epidemic since it refers to widespread geographical dispersion. Similarly, a high level of disease present consistently in a specific area denotes an endemic state, where the disease is consistently present but not necessarily at levels that exceed the norm. Lastly, describing a chronic health issue affecting a small population does not align with the acute nature of an epidemic, which involves a rise in cases over a short period rather than a long-term, stable situation. Thus, the definition focusing on the sudden and significant increase in cases provides the most accurate characterization of an epidemic.