Emergence of NDM-5-Positive Salmonella enterica Serovar Typhimurium Monophasic Variant ST34 in Hong Kong During 2020–2025

The emergence of carbapenem-resistant non-typhoidal Salmonella species (CR-NTS) has been observed in recent years, causing increasing challenges in the clinical management and control of Salmonella infections. However, CR-NTS had not been comprehensively studied in Hong Kong previously. We retrieved archived non-typhoidal Salmonella isolates demonstrating carbapenem resistance from five public hospitals in Hong Kong during January 2020–June 2025. The isolates were characterised by NG-TEST CARBA-5 and subjected to whole-genome sequencing (WGS) and phylogenetic analysis. Clinical information of CR-NTS cases was also reviewed. Fourteen CR-NTS isolates (0.3%, 14/4404) were identified during the study period. All 13 CR-NTS isolates (one isolate could not be recovered) were NDM (New Delhi metallo-β-lactamase)-positive, with the first case identified in March 2023. WGS revealed six Group B Salmonella monophasic variants of Salmonella enterica serovar Typhimurium ST34 harbouring the blaNDM-5 gene. The most common plasmid replicon co-present among blaNDM-5-positive isolates was IncHI2–IncHI2A (63.6%, 7/11). Among cases of CR-NTS in our study, self-limiting gastroenteritis was the most common presentation (84.6%, 11/13); none presented with invasive infections; travel history was present in 7.7% (1/13). Phylogenetic analysis showed the genotypic relatedness of the ST34 isolates identified in Hong Kong to those on the Chinese mainland, with the possibility of local CR-NTS acquisition via imported food sources. Our findings highlighted the importance of a One Health approach to the control of CR-NTS and the need for continuous antimicrobial resistance surveillance of Salmonella spp. in Hong Kong.