**Core Concept**
The World Health Organization (WHO) STEPS approach is a strategy for non-communicable disease (NCD) surveillance, focusing on a standardized, multi-step method to collect data on behavioral, physiological, and biochemical risk factors. This approach emphasizes the importance of surveillance in monitoring and controlling NCDs.

**Why the Correct Answer is Right**
The WHO STEPS approach involves three main steps:
1. **Step 1:** Behavioral risk factor surveys to collect data on tobacco use, physical activity, and dietary habits.
2. **Step 2:** Physical measurements, including blood pressure, height, and weight, to assess physiological risk factors.
3. **Step 3:** Biochemical measurements, such as blood glucose and lipid profiles, to identify individuals at risk of NCDs.
These steps enable healthcare professionals to identify high-risk individuals and provide targeted interventions to prevent and manage NCDs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the WHO STEPS approach is specifically designed for NCD surveillance, not infectious disease control.

**Option B:** This option is incorrect because the WHO STEPS approach focuses on behavioral, physiological, and biochemical risk factors, not just clinical diagnosis.

**Option C:** This option is incorrect because the WHO STEPS approach is a surveillance strategy, not a treatment protocol.

**Clinical Pearl / High-Yield Fact**
The WHO STEPS approach emphasizes the importance of surveillance in monitoring and controlling NCDs, which are a leading cause of morbidity and mortality worldwide.

**Correct Answer: D. Non-communicable disease surveillance.**