S. Infantis¶

At a Glance


Antigenic Formula	`6,7,14:r:1,5`
Serogroup	O:7 (C1)
NCBI Pathogen Detection	View isolates

Background Information¶

Salmonella enterica subsp. enterica serovar Infantis (antigenic formula 6,7,14:r:1,5) is a serovar of the O:7 (C₁) serogroup. This serovar was first reported in wild birds in Florida, USA in 1979. Serovar Infantis was identified as the most common serovar in broiler flocks (45.6%) and broiler meat (50.6%) across Europe. In human cases, serovar Infantis ranked as the fourth most prevalentserovar in non-typhoidal Salmonella (NTS) infections in Europe. Additionally, inthe United States, serovar Infantis was consistently among the top 10 serotypes responsible for reported human illnesses in 9 out of 10 years between 2010 and 2019, with the exception of 2012, when it ranked 11th. Since 2016, serovar Infantis has become one of the most frequently detected Salmonella serotypes originating from poultry sources in the United States.

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. Avivdemonstrated 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. A previous study noted that MDR Infantis strains carrying the pESI plasmid exhibited a higher rate of adherence to and invasion of human epithelial cells compared to pESI-negative strains. In birds, Drauch et al. found that broilers infected with pESI-positive Infantis displayed greater virulence than those infected with pESI-negative strains.

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 serovar Infantis is polyphyletic with two lineages identified and one stand-alone singleton that does not cluster with any other Salmonella Infantis isolates. 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.

Animal Reservoir¶

The main animal reservoir of serovar Infantis is poultry; however, at least one of Infantis clade is associated with swine.

Geographical Distribution¶

Serovar Infantis is distributed globally and is a common serovar in a number of countries.

Human/Animal Outbreaks¶

Numerous human outbreaks linked to poultry have been reported mainly in the US and Canada. Here are some examples.

Year	Location	Associated source	Number of cases
2024	US: multistate	Backyard poultry¹	470
2019	US: multistate	Raw chicken	129
2017	US: multistate	Papaya²	4
2013	Germany	Raw pork products	267
2013	US: multistate	Live poultry³	158
2012	US: multistate & Canada	Dry dog food	49
2012	US: multistate	Live poultry⁴	195
1999	Canada	Pig ear dog treats	30

¹ Multiple serovars, including Salmonella Altona, Cerro, Enteritidis, Indiana, Infantis, Johannesburg, Mbandaka, and Typhimurium, were linked to this outbreak. The case number represents the total number of cases associated with the outbreak and does not specifically indicate the number of people infected by Salmonella Infantis.

² This outbreak involved both Salmonella Newport (3 cases) and Infantis (1 case).

³ Salmonella Infantis, Lille, Newport, and Mbandaka were reported from 30 states.

⁴ Salmonella Infantis, Newport, and Lille were reported from 27 states.

Border Rejections¶

Multiple border rejections linked to serovar Infantis have been reported. Majority of them are associated with poultry. Here are some examples.

Year	Exporting country	Importing country	Associated source	Product category
2024	Poland	Italy	Frozen chicken meat¹	Poultry meat and poultry meat products
2023	Poland	Germany	Dog chews	Pet food
2020	Brazil	Germany	Black pepper²	Herbs and spices
2020	Russia	Finland	Maize	Feed materials

¹ Salmonella Enteritidis and Infantis were both found.

² Salmonella Infantis and Panama were both found.

Recalls¶

Multiple recalls linked to serovar Infantis have been reported. Majority of them are associated with poultry. Here are some examples.

Year	Location	Recalled food	Type
2023	Slovakia	Chicken eggs from Czech Republic	Eggs and egg products
2023	Czech Republic	Chicken breast from Ukraine	Poultry meat and poultry meat products
2021	US: WA	Uncured antipasto products	Meat and meat products (other than poultry)
2021	Norway	Frozen fish (Gourami) from Vietnam	Fish and fish products