Genomic epidemiology and antimicrobial resistance reveal local transmission dynamics of enteric fever in Shenzhen, one of the mega cities in China.

Objectives: Outbreak of enteric fever and the spread of antimicrobial-resistant Salmonella Typhi and S. Paratyphi pose significant public health challenges in low- and middle-income countries. Understanding the transmission dynamics of these pathogens is essential for developing effective control strategies.

Methods: We conducted phylogenomic analyses and integrated epidemiological data from 135 S. Typhi and 271 S. Paratyphi A isolates collected in Shenzhen from 2001 to 2017. Phylogenetic and temporal analyses were performed to identify prevalent genotypes and assess transmission patterns.

Results: Analyses of S. Typhi isolates in Shenzhen revealed high genetic diversity, with genotypes 3.2.1 (37.8%) and 2.1.7 (20%) being most prevalent. Genotype 3.2.1 formed an independent lineage due to mutations in the quinolone resistance determining region (QRDR). The multidrug-resistant haplotype 58 (genotype 4.3.1) has been present since 2006. S. Paratyphi A isolates were predominantly genotype 2.3.3 (98.5%). Pathogen exchange occurred with at least four other provinces. A cutoff of ≤3 single nucleotide polymorphisms (SNPs) was effective for outbreak investigation, and 22 genomic clusters were found, suggesting undetected outbreaks or transmission events. While 80% of isolates were susceptible to first-line antibiotics, 16.9% of S. Paratyphi A isolates were multidrug-resistant.

Conclusions: This study provides insights into the transmission dynamics of enteric fever in Shenzhen, underscoring the need for ongoing genomic surveillance to manage and control outbreaks effectively.