Los Angeles Shigellosis Outbreak Caused by Mutation

In 2024, California led the United States in extensively drug-resistant (XDR) Shigellosis outbreaks, with 4,365 cases reported out of a national total of 20,621. A Brief Report published by AJIC on December 9, 2024, detailed a mutation in the Shigella sonnei bacteria, making it resistant to five classes of antibiotics commonly used to treat such infections, including cephalosporins.

This XDR Shigella strain is unique to Los Angeles County and underscores the rapid spread of drug-resistant Shigella in the U.S. Since its first detection in California in 2017, the prevalence of XDR Shigella has risen significantly, with 12% of Shigella isolates reported as XDR from January through May 2024. Shigella sonnei isolates accounted for 78% of cases.

The U.S. CDC estimates that Shigellosis is the third most common bacterial enteric disease, with 20,621 cases confirmed by the end of 2024. In 2023, the CDC reported 17,176 cases nationwide.

Efforts to combat this outbreak include the development of the Shigella4V (S4V) vaccine by Valneva SE and LimmaTech Biologics AG, which entered a Phase 2b clinical trial on November 13, 2024. The U.S. FDA has granted Shigella4V Fast Track designation, indicating the urgency of addressing this public health challenge.