A Ten-Year Retrospective Survey of Antimicrobial Susceptibility Patterns among Salmonella enterica subsp. enterica Serovar Typhi Isolates in Ontario, Canada

The epidemiology and treatment of typhoid fever are complicated by the emergence and spread of Salmonella enterica subsp. enterica serovar Typhi lineages with resistance to many antimicrobial agents critical for therapy. Current information on the susceptibility patterns of S. Typhi isolates identified in regions where typhoid fever is not endemic is important as these are often acquired after traveling to countries of endemicity where resistant strains circulate. Here, we report a 10-year retrospective survey of S. Typhi antimicrobial susceptibility patterns among 858 unique patient isolates that underwent reference laboratory testing in Ontario, Canada, between 2010 and 2019. Antimicrobial susceptibility patterns remained stable for ampicillin (average, 78.7% susceptible), azithromycin (average, 99.4% susceptible) ertapenem (average, 100.0% susceptible), meropenem (average, 100.0% susceptible), and trimethoprim-sulfamethoxazole (average, 78.2% susceptible) during the study period; however, nonsusceptibility to ciprofloxacin and ceftriaxone increased. While ceftriaxone-resistant isolates comprised 1.6% of the total isolates overall, they represented 10.1% of the total isolates tested in 2019, indicating a significant increase over time. Our findings suggest that when selecting empirical therapy, health care providers should strongly consider current trends in antimicrobial susceptibility and investigate the patient’s exposure risk to gauge whether a suspected typhoid infection may be caused by a potentially resistant S. Typhi strain. IMPORTANCE This work provides an updated summary of the antimicrobial susceptibility patterns among Salmonella Typhi strains isolated from patients in Ontario, Canada.