Most shigellosis cases caused by S. flexneri, S. sonnei

Data from the Global Enteric Multicenter Study suggest that a vaccine for Shigella must protect against S. sonnei and 15 serotypes of S. flexneri to provide the broadest protection against shigellosis.

“Based on clinical severity, disease burden and emergence of antimicrobial resistance, Shigella is a prime target for vaccine development,” researchers from the Center for Vaccine Development, University of Maryland School of Medicine, wrote in Clinical Infectious Diseases. “Most Shigella vaccines in clinical development are based on eliciting protection against multiple epidemiologically important serotypes. Accordingly, to rationally guide vaccine formulation, it is imperative to have robust data on the distribution of Shigella serotypes associated with shigellosis.”

The Global Enteric Multicenter Study (GEMS) was an age-stratified, matched case-control study of moderate-to-severe diarrheal illness in children aged 0 to 59 months seeking care at sites in sub-Saharan Africa and South Asia. For this study, researchers evaluated 1,130 Shigella isolates from cases enrolled in GEMS and 219 isolates from controls without diarrhea to identify the most common serotypes.

Most of the isolates were S. flexneri (65.9%) or S. sonnei (23.7%). Four serotypes of S. flexneri —2a, 2b, 3a and 6 — accounted for 78% of the S. flexneri isolates. S. dysenteriae accounted for 5% of the Shigella isolates and S. boydii accounted for 5.4% of the isolates.

“Serotyping of the GEMS Shigella isolates offers optimism that a quadrivalent vaccine containing S. sonnei and three serotype/subserotypes of S. flexneri (2a, 3a and 6) can provide broad coverage against Shigella causing the majority of endemic pediatric shigellosis in the developing world and also provide broad coverage for travelers,” the researchers wrote.

Disclosure: The researchers report no relevant financial disclosures.