**Core Concept**
A point source epidemic is a type of outbreak that occurs when a group of people are exposed to a pathogen or disease-causing agent from a single source, resulting in a rapid increase in cases. This type of epidemic typically has a distinct incubation period and a rapid rise and fall in cases.

**Why the Correct Answer is Right**
Option B (bd) is correct because a point source epidemic can be caused by non-infectious diseases, such as food poisoning or chemical exposure. Additionally, secondary waves are possible in point source epidemics if the initial cases are not properly contained or if there is continued exposure to the source. The correct answer highlights the importance of considering non-infectious causes and the possibility of secondary waves in point source epidemics.

**Why Each Wrong Option is Incorrect**
**Option A:** Rapid rise and fall is a characteristic of point source epidemics, so this statement is true.
**Option C:** Cases can occur even after the incubation period has ended, as the disease may not become apparent until after the initial exposure. This statement is true.
**Option E:** Secondary waves can occur in point source epidemics, making this statement false.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that point source epidemics can be caused by both infectious and non-infectious agents, and to consider the possibility of secondary waves when investigating an outbreak.

✓ Correct Answer: B. bd. Non-infectious diseases and secondary waves can occur in point source epidemics.