In the WHO operational classification of leprosy, which of the following is the criterion used to categorize a patient as multibacillary (MB) leprosy?

Explanation

## WHO Operational Classification of Leprosy The WHO simplified operational classification divides leprosy into **paucibacillary (PB)** and **multibacillary (MB)** based primarily on the **number of skin lesions** — a purely clinical criterion designed for field settings where laboratory facilities may not be available. ### WHO Operational Classification Criteria (2018 Guidelines) **Key Point:** The **primary criterion** in the WHO operational classification is the **number of skin lesions**, not the bacillary index (BI). The BI is used in the Ridley-Jopling classification and in research settings, but the WHO field classification relies on lesion count. | Criterion | Paucibacillary (PB) | Multibacillary (MB) | |---|---|---| | **Skin lesions** | 1–5 lesions | **>5 lesions** | | **Smear (if available)** | Smear-negative | Smear-positive | ### Why Option A (>5 skin lesions) is Correct - The WHO operational classification was introduced to simplify leprosy management in endemic countries where slit-skin smear facilities are often unavailable. - **>5 skin lesions → MB leprosy → 12-month MDT regimen** - **1–5 skin lesions → PB leprosy → 6-month MDT regimen** - This criterion is explicitly stated in WHO Guidelines for the Diagnosis, Treatment and Prevention of Leprosy (2018) and Park's Textbook of Preventive and Social Medicine (26th edition). ### Why Option B (BI ≥2+) is Incorrect as the Primary Criterion - The bacillary index (BI) is a **supplementary** criterion used when smear facilities are available, but it is **not** the defining operational criterion in the WHO field classification. - A BI ≥2+ would classify a patient as MB, but this is secondary to the lesion-count rule in operational practice. - The Ridley-Jopling classification uses BI as a primary tool; the WHO operational classification does not. ### Why Other Options are Incorrect - **Positive lepromin test (Option C):** A positive lepromin test indicates good cell-mediated immunity (tuberculoid end of spectrum) and is associated with PB leprosy, not MB. It is not used in WHO operational classification. - **Presence of nerve thickening (Option D):** Nerve involvement is a diagnostic feature of leprosy but is not the criterion for PB vs. MB classification in the WHO operational system. **High-Yield:** The WHO operational classification is designed for **field use** — lesion count is the practical, accessible criterion. MDT duration: PB = 6 months, MB = 12 months. **Clinical Pearl:** A patient with 6 skin lesions is classified as **MB** and receives 12-month MDT regardless of smear result. Lesion count is the operational cornerstone per WHO 2018 guidelines (Park's PSM, 26th edition). **Mnemonic:** **>5 lesions = MB** (More than Five = Multibacillary).