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

Explanation

## WHO Operational Classification of Leprosy The WHO simplified operational classification divides leprosy into two categories based on clinical and bacteriological criteria, determining treatment duration and regimen. ### Multibacillary (MB) Leprosy — WHO Criteria **Key Point:** According to the WHO operational classification (as described in Park's Textbook of Preventive and Social Medicine, 26th edition), a patient is classified as MB if they have **more than 5 skin lesions** and/or **involvement of more than one peripheral nerve** (with or without a positive slit-skin smear). **Diagnostic Criteria for MB (any one of the following):** 1. **More than 5 skin lesions** (primary clinical criterion) 2. **Involvement of more than one peripheral nerve** (clinical criterion) 3. **Positive slit-skin smear** (bacteriological criterion — AFB present at any site) **High-Yield:** The WHO operational classification is a *field-level* tool designed for use even where slit-skin smear facilities are unavailable. The **clinical criteria (>5 lesions OR >1 nerve)** are the primary operational criteria; smear positivity is an additional confirmatory criterion, not the defining one. ### Why Option A is Incorrect as the Primary Criterion Option A states "Bacillary index ≥2+ on slit-skin smear **or** presence of bacilli in any skin lesion." While smear positivity does classify a patient as MB, the WHO operational classification is explicitly designed to function **without** smear microscopy in resource-limited settings. The defining operational criterion is the **clinical** one: >5 lesions and/or >1 nerve involved (Option C). Restricting the definition to smear findings alone misrepresents the WHO framework. ### Paucibacillary (PB) Leprosy **Diagnostic Criteria for PB:** - ≤5 skin lesions AND ≤1 peripheral nerve involved AND negative slit-skin smear - Requires 6-month MDT regimen ### Comparison: MB vs PB | Feature | Multibacillary (MB) | Paucibacillary (PB) | |---------|-------------------|-------------------| | **Skin lesions** | >5 | ≤5 | | **Nerves involved** | >1 | ≤1 | | **Slit-skin smear** | Positive (if done) | Negative | | **MDT duration** | 12 months | 6 months | **Clinical Pearl:** The WHO operational classification is simpler than Ridley-Jopling and is used globally for standardized treatment protocols. The clinical criteria (>5 lesions / >1 nerve) allow classification even without laboratory support. **Mnemonic:** **MB = More than 5 lesions = More months (12)** of treatment; **PB = Paucity (≤5 lesions) = Partial months (6)** of treatment. [cite: Park 26e Ch 8; WHO Guide to Eliminate Leprosy as a Public Health Problem]