**Core Concept**
Primary prevention aims to prevent the occurrence of a disease in a susceptible individual before the disease process begins. This approach targets the root causes of disease, such as lifestyle modifications, vaccinations, and environmental changes.

**Why the Correct Answer is Right**
Primary prevention involves interventions that eliminate or reduce the risk factors for a disease. For instance, vaccination programs prevent the spread of infectious diseases by generating immunity in the population. Similarly, a healthy diet and regular exercise can prevent chronic diseases like heart disease and diabetes. This approach is essential in controlling the incidence of diseases and improving overall public health.

**Why Each Wrong Option is Incorrect**
**Option A:** Secondary prevention involves early detection and treatment of a disease, not prevention of disease occurrence.
**Option B:** Tertiary prevention focuses on reducing the impact of an ongoing disease, such as managing complications and improving quality of life.
**Option C:** Quaternary prevention aims to minimize the harm caused by unnecessary medical interventions and health care overuse, which is not directly related to disease prevention.

**Clinical Pearl / High-Yield Fact**
The World Health Organization (WHO) defines primary prevention as "all measures taken to prevent disease before the disease occurs." This includes health promotion, disease prevention, and health education.

**Correct Answer: D. Primary prevention is aimed at preventing disease occurrence in a susceptible individual before the disease process begins.**