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In the U.S. and Europe, it ranks among the top ten serovars. S. Infantis has been reported in North America (U.S. and Canada), South America (Argentina, Brazil), Oceania (Australia and New Zealand), Europe (The Netherlands, Finland, Hungary, and Russia), and Asia (Japan).

NCBI PD link for serovar Infantis: https://www.ncbi.nlm.nih.gov/pathogens/isolates/#(taxgroup_name:%22Salmonella%20enterica%22)%20AND%20computed_types:(%22serotype=Infantis%22)

Genetic characteristics: In European countries, a multidrug-resistant (MDR) strain of serovar Infantis was disseminated; this strain emerged from broilers in Hungary (Hungarian clone of serovar Infantis). Resistant pattern of this Hungarian clone included resistance to: nalidixic acid, streptomycin, sulphonamide, and tetracycline. In Italy, an MDR strain of serovar Infantis that showed resistance to ampicillin, chloramphenicol, streptomycin, sulphonamide, tetracycline, kanamycin and trimethoprim/sulfamethoxazole emerged in 2005-06. Later, Franco et al. identified the spread of a MDR, ESBL-producing (bla_CTX-M-1) clone of serovar Infantis harboring a conjugative megaplasmid (pSEI~ 280-320 kb) in the Italian broiler chicken industry and throughout the food chain. Aviv demonstrated that, despite its substantial size, the pESI plasmid does not hinder metabolic activity in vitro and has recently become firmly established in the domestic Infantis population. Through a mouse model, they showed that pESI can be horizontally transferred to the gut microbiota, including to commensal Escherichia coli strains after Infantis infection.

The CDC has identified REPJFX01 as a persistent, MDR strain of Salmonella Infantis (hereafter referred to as REP Strain) that has led to illnesses and outbreaks both in the US and worldwide. This strain was first documented in PulseNet in 2012. It has spread to individuals in the United States through contaminated chicken and has also been linked to exposures during international travel. The REP strain show resistance to multiple antimicrobials, including key first-line and alternative treatments such as ampicillin, ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole. Meanwhile, this strain exhibits relatively high genetic diversity, with isolates differing by up to 82 alleles from one another, as determined by cgMLST (core genome multilocus sequence typing). Chen et al. revealed that Infantis-A-1-3, a chicken-associated clade estimated to have emerged in 1933, includes a clonal sub-clade which emerged in 1990 and represents 32% of the isolates, with an increase in the proportion of isolates collected from chicken or chicken-related sources.

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