Highlights
- REPJFX01 is a persistent strain of multidrug-resistant Salmonella Infantis bacteria that has caused illnesses and outbreaks in the United States and globally.
- This strain has spread to people through contaminated chicken in the United States and through exposures during international travel.
- REPJFX01 infections may not be treatable with some antibiotics normally used to treat serious Salmonella infections because they are resistant to these antibiotics.
At a glance
- Raw chicken products: 1 outbreak
- Mechanically separated chicken (suspected): 2 outbreaks
- Cabbage salsa (suspected; cross-contamination): 1 outbreak
- Person-to-person contact: 2 outbreaks
Key findings
REPJFX01 is a persistent, multidrug-resistant strain of Salmonella Infantis bacteria that has caused illnesses and outbreaks in the United States and globally.
Illness caused by this strain was first reported in 2012.
Genetically diverse
This strain of Salmonella Infantis is relatively diverse genetically based on results from whole genome sequencing (WGS).
Genetic diversity can increase over time as strains pass among human hosts, animal hosts, and environmental settings, each with different selective pressures. Understanding this genetic diversity helps public health officials identify related illnesses and better understand how these strains continue to spread and persist over time.
What the data show
Illnesses and outbreaks
Lab-confirmed REPJFX01 infections
Among 542 patients with information available
- 29% were hospitalized
- 5% were admitted to the intensive care unit
Among 542 patients with information available, 1% died
Median age: 55 years (interquartile range: 27–70 years)
63% of ill people were female
Stool in 65% and urine in 28% of cases
REPJFX01 has spread to people through contaminated chicken in the United States and through exposures during international travel
Among 542 patients with information available, 10% traveled internationally in the 7 days before their illness began.
Most traveled to the Dominican Republic (38%), Peru (24%), or Ecuador (12%).
Outbreaks and other investigations
Although most enteric illnesses—including those caused by REPJFX01—are not part of an outbreak, investigation of outbreaks provides information that increases our understanding of bacteria, sources, settings, and factors that contribute to illness.
CDC and local, state, and federal public health and regulatory partners have investigated several clusters of Salmonella Infantis illnesses as possible outbreaks caused by the REPJFX01 strain.
Summary of selected multistate outbreaks and other investigations
| Outbreak | Dates people became ill | Outbreak source |
WGS-linked Illnesses |
Number of states with WGS-linked Illnesses |
More information |
|---|---|---|---|---|---|
| A | May 15– August 19, 2016 |
Mechanically separated chicken (suspected) |
3 | 1 | |
| B | January 5– March 28, 2017 |
Unknown | 7 | 6 | |
| C | February 9– July 23, 2017 |
Unknown | 39 | 22 | |
| D | April 25– June 7, 2017 |
Unknown | 5 | 3 | |
| E | December 1, 2017–January 2, 2018 | Person-to-person (child daycare) | 3 | 1 | |
| F | March 1–15, 2018 | Unknown | 2 | 1 | |
| G | June 23–September 14, 2018 | Unknown | 12 | 7 | |
| H | July 28–October 10, 2018 | Unknown | 10 | 7 | |
| I | April 5–September 28, 2019 | Person-to-person (long-term care facility) | 6 | 1 | |
| J | October 10, 2018–January 27, 2019 | Raw chicken products | 113 | 31 | CDC Investigation Notice USDA Outbreak After Action Report |
| K | July 24–August 5, 2019 | Cabbage salsa (suspected) | 5 | 1 | Possible cross-contamination of restaurant item |
| L | August 2–September 4, 2019 | Unknown | 1 | 1 | |
| M | September 24–October 7, 2019 | Mechanically separated chicken (suspected) | 1 | 1 | |
| N | February 25–March 10, 2020 | Restaurant, unknown vehicle | 8 | 1 | Multiple health code violations; one ill food handler |
Selected publications regarding REPJFX01 investigations
- Trends in a persistent strain of multidrug-resistant Salmonella Infantis (REPJFX01) in humans and chickens | United States, 2010–2023 (2026)
- Epidemiology and antimicrobial resistance of Salmonella Infantis in the United States: infections and emergence of a multidrug-resistant strain during 1979–2022 (2026)
- A multidrug-resistant Salmonella Infantis clone is spreading and recombining in the United States (2021)
- Carriage and gene content variability of the pESI-like plasmid associated with Salmonella Infantis recently established in U.S. poultry production (2020)
- CTX-M-65 extended-spectrum β-lactamase-producing Salmonella Infantis | United States (2018)
- Outbreak epidemiologically linked with a composite product of beef, mechanically separated chicken, and textured vegetable protein contaminated with multiple serotypes of Salmonella including multidrug-resistant Infantis | California, 2016 (2018)
- Comparative analysis of extended-spectrum-β-Lactamase CTX-M-65-producing Salmonella Infantis isolates from humans, food animals, and retail chickens | United States (2017)
Timeline
Map
Laboratory data
Whole genome sequencing analysis
Bacteria in this strain are within 88 allele differences of one another by core genome multilocus sequence typing.
This is more genetically diverse than typical multistate foodborne outbreaks, in which bacteria generally are within 10 allele differences of one another.
Genetic diversity can increase over time as strains pass among human hosts, animal hosts, and environmental settings, each with different selective pressures. Understanding this genetic diversity helps public health officials identify related illnesses and better understand how these strains continue to spread and persist over time.
Isolates from food, animal, and environmental samples
Information from more than 9,000 REPJFX01 isolates from non-human sources has been reported to PulseNet, with the earliest in 2014.
Most isolates are from chicken samples collected by the USDA Food Safety and Inspection Service (FSIS), including 6,721 from FSIS sampling of food and food products and 743 from FSIS sampling of intestinal (cecal) content. Other non-human sources of bacteria sequences reported to PulseNet include
- Turkey (306 isolates)
- Pork or swine (64)
- Beef or cattle (54)
- Water (24); and
- Other food, animal, and environmental sources (65).
Although WGS data from U.S. Food and Drug Administration (FDA) samples have not always been submitted to PulseNet, more than 1,000 food and environmental isolates collected through FDA sampling programs are highly related to REPJFX01 isolates by WGS, including many samples from retail chicken products.
More information about these isolates can be found through the National Center for Biotechnology Information or the NARMS Now: Integrated Data platform.
Genomic information
The National Center for Biotechnology Information (NCBI) advances science and health by providing access to biomedical and genomic information.
Antimicrobial resistance
The National Antimicrobial Resistance Monitoring System (NARMS) is a national public health surveillance system that tracks antimicrobial resistance for certain intestinal bacteria from ill people (CDC), food animals (USDA), and retail meats (FDA) in the United States. The NARMS program helps protect public health by providing information about emerging antimicrobial resistance, the ways in which resistance spreads, and how resistant infections differ from susceptible infections.
Bacteria from most ill people's samples showed resistance to multiple antibiotics, including several recommended for first-line or alternative treatment: ampicillin, ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole. Among a subset of 223 patients who received antibiotics recommended as first-line or alternative treatment for salmonellosis, 73% had an isolate that was resistant to that antibiotic
Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed, some REPJFX01 illnesses may not be treatable with commonly recommended antibiotics and may require a different antibiotic choice. When possible, healthcare providers should use antimicrobial susceptibility testing results to guide treatment.
Collaborate with CDC
Interested in collaborating on a project related to this strain? Contact CDC at REPStrains@cdc.gov.
About the data
Information provided in the "Morbidity and mortality," "Antibiotic treatment," and "Travel" rows is based on data from a subset of 542 patients with records in the Foodborne Diseases Active Surveillance Network (FoodNet) during 2018–2024.
Lab-confirmed cases are only a small part of the actual number of illnesses. Most people do not seek medical care and even fewer submit a clinical (e.g., stool) specimen.
PulseNet transitioned to using WGS as the standard subtyping method for Salmonella in July 2019. Before then, not all Salmonella isolates reported to PulseNet had WGS data available. Isolates are identified as part of this strain based on WGS. As a result, the number of people with lab-confirmed illness caused by this strain before 2019 may be underrepresented.
Outbreak dates are based on reported or estimated illness onset dates.
Confirmed sources were identified by epidemiology plus traceback or laboratory data. Suspected sources were identified by epidemiology only. More information about determining outbreak sources is available in the latest summary of possible multistate enteric disease outbreaks.
The number of illnesses and states listed per outbreak in this table may differ from other reports (e.g., publications). This is because the table only includes illnesses with WGS data that meet the allele range for this REP strain (see Genomic Information section).
Outbreak data were obtained from the System for Enteric Disease Response, Investigation, and Coordination (SEDRIC) and the National Outbreak Reporting System (NORS).
Selected publications on Salmonella Infantis are for reference. Other publications regarding this strain are available.
Includes 4,410 human illnesses for which information was reported as of December 31, 2025.
The "by year" view of the timeline labels each bar as "January" because of a limitation in the data visualization. Switch to the "by month" view to see a more detailed breakdown of when people became ill.
Includes 4,410 human illnesses for which information was reported as of December 31, 2025. Illness year is based on the date of isolate collection.
Includes 9,588 non-human isolates for which information was reported as of December 31, 2025. Some collection dates have been estimated from other reported information.
Isolates sequenced by FSIS from non-chicken sources included
- 25 isolates from cecal contents (part of the animals' intestines)
- 1 isolate from a food animal, and
- 337 isolates from food, food products, and environmental sources
Isolates sequenced by FSIS include isolates collected by the Agricultural Marketing Service (AMS).
The exploratory testing was performed on rehang samples (prior to evisceration and prior to application of all interventions).
The single nucleotide polymorphism (SNP) tree provided by NCBI's Pathogen Detection Pipeline in the link above may include isolates that are not considered part of this strain. The difference in allele vs. SNP thresholds occurs because NCBI and PulseNet use different analysis pipelines.
The link is provided to give context to the overall genetic relatedness of the strain reported on this page and to provide links to raw sequence files.
The SNP trees on NCBI's Pathogen Detection Pipeline are updated more frequently than this web page.
Resistance information was available for 4,372 cases. Resistance was determined based on the results of antimicrobial susceptibility testing when available (210 isolates). Otherwise, resistance was predicted based on whole genome sequencing (4,162 isolates).
Ciprofloxacin data includes isolates with an intermediate interpretation on antimicrobial susceptibility testing or a single quinolone resistance mechanism (a single mechanism is typically associated with intermediate interpretation in Salmonella).
Resistance determination was based only on predicted resistance from WGS for hygromycin, tobramycin, trimethoprim, kanamycin, and fosfomycin.
This page was last updated on this date. Updates may include minor edits, image changes, or other modifications to page content.
The information on this page was last reviewed by subject matter experts to ensure accuracy.