Outbreak of Ceftriaxone-Resistant Salmonella enterica Serovar Typhi, Bangladesh, 2024

Abstract

We report an outbreak of ceftriaxone-resistant Salmonella enterica serovar Typhi in Bangladesh; 47 cases were identified during April-September 2024. Isolates belonged to genotype 4.3.1.2 and harbored the bla_CTX-M-15 gene on the pCROB1 plasmid. This genotype-plasmid lineage represents a recent introduction, calling for strengthened surveillance, antimicrobial stewardship, and vaccination strategies.

Keywords: Bangladesh; Salmonella Typhi; Salmonella enterica serovar Typhi; antimicrobial resistance; bacteria; ceftriaxone resistance; typhoid fever.

Figure 1

Overview of study of an outbreak of ceftriaxone-resistant Salmonella enterica serovar Typhi in Bangladesh, 2024. A) Locations of the 20 study clinics across 11 districts of Bangladesh (blue dots). White indicates districts where the study clinics are located; gray indicates districts not included in this study. B) Geographic distribution of CefR Salmonella Typhi isolates across Bangladesh. The size of each red dot represents the number of isolates per district. C) Timeline of the surveillance network, showing the inclusion of clinics (text labels) and the total number of Salmonella Typhi isolates and CefR isolates detected. Our surveillance efforts began in January 2023 with 3 clinics in Dhaka; more clinics in various locations across Bangladesh were added through May 2024. CefR, ceftriaxone-resistant.

Figure 2

Annotated map of plasmid pCROB1 from study of an outbreak of ceftriaxone-resistant Salmonella enterica serovar Typhi, Bangladesh, 2024. pCROB1 harbors the bla_CTX-M-15 gene and includes an intact phage element, as annotated using PHASTEST (12). Tracks around the plasmid map highlight GC content and predicted ORFs. GC, guanine and cytosine nucleotides; OFR, open reading frame.

Figure 3

Phylogenetic tree of Salmonella Typhi genotype 4.3.1, including the 17 CefR 4.3.1.2.B1 strains detected in findings from a study of an outbreak of CefR S. enterica serovar Typhi, Bangladesh, 2024. A) Phylogenetic tree of 546 genomes belonging to genotype 4.3.1 and its subtypes. CefR strains sequenced in our study belong to genotype 4.3.1 and are highlighted in yellow. Tree was built following a pipeline described earlier (10) and displays different CefR genes, countries of isolation, and associated plasmid elements. For context, 529 genomes from genotype 4.3.1 and its subtypes were also included. Of those, 249 (10%) were randomly selected from 2,567 genomes (genotype 4.3.1.2 and subtypes) available on Pathogenwatch by genotype, year, and country (accessions available for 2,542; accessed on 14 July 2024), and 280 were from previous studies conducted in Bangladesh, India, and Pakistan (14). B) Zoomed-in view of the subclade containing the CefR strains from our study in Bangladesh. Scale bars indicate mean nucleotide substitutions per site. CefR, ceftriaxone-resistant.