Persistent Strain of Salmonella Infantis (REPJFX01) Linked to Chicken
Posted July 21, 2023
Posted July 13, 2023
Food Safety Alert/Investigation Notice
CDC, public health, and regulatory officials in several states, and _____________________________ are investigating a multistate outbreak of Salmonella Infantis infections with this persistent strain linked to ________________. Do not eat, sell, or serve ______________________.
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 to PulseNet in 2012. As of December 31, 2022, information from 2,900 patients with REPJFX01 infection was reported to PulseNet. The median age of patients was 54 years (interquartile range, 27–70 years), and 62% were female. The isolate source was stool in 65% and urine in 27% of cases. Illnesses caused by this strain occur year-round but are most common in July and August. In the past, REPJFX01 has spread to people through contaminated chicken in the United States and through exposures during international travel.
Among a subset of 251 patients with records in Foodborne Disease Active Surveillance Network (FoodNet) during 2018–2020, 10% of patients traveled internationally in the 7 days before their illness began; most traveled to the Dominican Republic (45%), Peru (25%), or Ecuador (10%). Among the same subset of patients, 29% were hospitalized, 7% were admitted to the intensive care unit, and fewer than 1% died. Among 85 patients who received antibiotics recommended as first-line or alternative treatment for salmonellosis, 78% had an isolate that was resistant to that antibiotic.
This strain of Salmonella Infantis is relatively diverse genetically. Bacteria in the strain are within 82 allele differences of one another by core genome multilocus sequence typing (cgMLST). This is more genetically diverse than typical multistate foodborne outbreaks, in which bacteria generally fall within 10 allele differences of one another.
What is a persistent strain?
CDC uses “persistent” to describe some strains of bacteria that have caused illness for years. The strains continue to cause illness, even though the number of illnesses they cause might vary over time. The strains are sometimes linked to more than one source, making them harder to control.
|Antimicrobial Resistance Profile||Multidrug resistant (details below)|
|First Detection||June 2012|
|Illnesses Reported in PulseNet||2,900|
|Identified outbreak sources*
*Confirmed sources were implicated by epidemiologic
Last Updated: December 31, 2022
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. Moreover, lab-confirmed cases comprise only a small portion of the true number of illnesses that occur because most people do not seek medical care and even fewer submit a clinical (e.g., stool) specimen.
CDC and local, state, and federal health and regulatory partners have investigated several clusters of Salmonella Infantis illness as possible outbreaks caused by the REPJFX01 strain.
Summary of Selected Multistate Outbreaks and Other Investigations
|Geographic Location of
|Number of States
|Outbreak A||May 15–
August 19, 2016
|Outbreak B||January 5–
March 28, 2017
|Outbreak C||February 9–
July 23, 2017
|Outbreak D||April 25–
June 7, 2017
|Outbreak E||June 23–
September 14, 2018
|Outbreak F||July 28–
October 10, 2018
|Outbreak G||October 10, 2018–
January 27, 2019
|Raw chicken products
* Outbreak dates are based on reported or estimated illness onset dates.
† Confirmed sources were implicated by epidemiologic plus traceback or laboratory data. Suspected sources were implicated by epidemiologic data only. More info
‡ The geographic location of a confirmed outbreak source may not always be known. This can happen when a food containing multiple ingredients (e.g., bagged salad blend) is confirmed as the source, but the evidence cannot implicate a specific source or when evidence confirms an outbreak source but traceback cannot pinpoint the exact geographic location of the source.
Selected Publications* Regarding REPJFX01 Investigations
|A multidrug-resistant Salmonella Infantis clone is spreading and recombining in the United States
|Carriage and gene content variability of the pESI-like plasmid associated with Salmonella Infantis recently established in United States poultry production
|CTX-M-65 extended-spectrum β-lactamase-producing Salmonella enterica serotype Infantis, United States
|Outbreak epidemiologically linked with a composite product of beef, mechanically separated chicken and textured vegetable protein contaminated with multiple serotypes of Salmonella enterica including multidrug-resistant Infantis, California 2016
|Comparative analysis of extended-spectrum-β-Lactamase CTX-M-65-producing Salmonella enterica serovar Infantis isolates from humans, food animals, and retail chickens in the United States
* Selected publications on Salmonella Infantis are for reference; other publications regarding the bacteria are available.
This timeline, called an epidemiologic curve, shows when people got sick.
People with Salmonella Infantis illnesses caused by the REPJFX01 strain, by month of isolate collection, 2012–2022*,†
* Includes N=2,900 human illnesses for which information was reported as of December 31, 2022.
† PulseNet transitioned to using whole genome sequencing (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.
This map shows where sick people lived.
Salmonella Infantis illnesses caused by the REPJFX01 strain, by state, 2012–2022*
* Illness year is based on the date of isolate collection.
Whole Genome Sequencing analysis
Bacteria in this strain are within 82 allele differences of one another by cgMLST core genome multilocus sequence typing (cgMLST). This is more genetically diverse than typical multistate foodborne outbreaks, in which bacteria generally fall within 10 allele differences of one another.
Isolates from food, animal, and environmental samples
Information from more than 6,000 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 U.S. Department of Agriculture Food Safety and Inspection Service (FSIS): 4,176 are from FSIS sampling of food and food products and 345 are from FSIS sampling of intestinal (cecal) content. Other non-human sources of bacteria sequences reported to PulseNet include turkey (222 isolates); pork (56); beef (35); water (20); and other food, animal, and environmental sources (33).
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 (see below) or the NARMS Now: Integrated Data platform.
Number of REPJFX01 isolates from non-human sources submitted to PulseNet, by month of sample collection, 2012–2022*
* Includes N=6,127 non-human isolates for which information was reported as of December 31, 2022. Some collection dates have been estimated from other reported information.
† This exploratory testing was performed on rehang samples (prior to evisceration and prior to application of all interventions).
FSIS = Food Safety Inspection Service, U.S. Department of Agriculture
The National Center for Biotechnology Information (NCBI) advances science and health by providing access to biomedical and genomic information. To view the full SNP cluster, click on the link below; then within NCBI’s platform click the link underneath the “SNP Cluster” column.
SNP Cluster*: Isolates Browser – Pathogen Detection – NCBI (nih.gov).
* The SNP (single nucleotide polymorphism) 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’s Pathogen Detection Pipeline uses an analysis pipeline different from the one used by CDC PulseNet. The link is provided to give context to the overall genetic relatedness of the strain reported on this page, as well as to provide links to raw sequence files. Moreover, the SNP trees on NCBI’s Pathogen Detection Pipeline are updated more frequently than this web page.
The National Antimicrobial Resistance Monitoring System (NARMS) is a national public health surveillance system that tracks antimicrobial resistance for certain intestinal bacteria from sick 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 is spread, and how resistant infections differ from susceptible infections.
Bacteria from most sick people’s samples showed resistance to multiple antimicrobials, including several that are recommended for first-line or alternative treatment: ampicillin, ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole. Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed, some illnesses resulting from REPJFX01 may be difficult to treat with commonly recommended antibiotics and may require a different antibiotic choice.