Enteric pathogens – predominant Shigella species in India Epidemiology question: Which Shigella species is most commonly isolated (predominant) in India during shigellosis outbreaks and sporadic cases?

Introduction / Context:
Shigellosis is a significant cause of bacillary dysentery. Species distribution varies by region and development level. Recognizing the predominant species helps guide diagnostics and public health measures.

Given Data / Assumptions:

• The question focuses on India.
• Shigella comprises four species: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei.
• Species prevalence patterns differ between low- and high-income settings.

Concept / Approach:
In many developing regions, Shigella flexneri predominates in children and adults, while Shigella sonnei is more common in industrialized nations. Shigella dysenteriae type 1 causes severe epidemics but is less frequently isolated overall. Shigella boydii remains relatively uncommon and geographically restricted.

Step-by-Step Solution:
Identify the region (India) with epidemiology consistent with S. flexneri predominance.Compare to S. sonnei (industrialized countries) and S. dysenteriae (episodic outbreaks).Choose S. flexneri as the most frequent isolate.

Verification / Alternative check:
National surveillance reports and multicenter studies in South Asia routinely highlight S. flexneri as the leading cause of shigellosis, with periodic S. dysenteriae outbreaks.

Why Other Options Are Wrong:

• S. sonnei: predominant in high-income settings.
• S. dysenteriae: severe but less commonly isolated overall.
• S. boydii: relatively uncommon.
• All equally: contradicts regional data.

Common Pitfalls:
Generalizing data from one region to another; species prevalence is context-dependent.

Final Answer:
Shigella flexneri.