The U.S. Department of Agriculture’s Food Safety and Inspection Service (USDA’s FSIS) has published an after-action review of a foodborne illness outbreak that was linked to chicken products involving a multi-drug resistant (MDR) Salmonella Infantis strain. The outbreak, which occurred from May 2018 to February 2019, was the first time that FSIS identified a strain as “persistent,” and made evident the importance of increased, early communication between regulatory agencies and industry.

The outbreak discussed in the review caused 129 cases of salmonellosis across 32 states, resulting in 25 hospitalizations and one death. Although FSIS and the U.S. Centers for Disease Control and Prevention (CDC) investigated the outbreak, no product recalls were issued as the agencies were unable to identify any FSIS-regulated establishment as the source of the outbreak. Traceback efforts were unsuccessful due to a lack of available exposure and shopper purchase information.

Investigators were able to associate chicken products with the outbreak through pulsed-field gel electrophoresis (PFGE), however. Analysis revealed the presence of the strain in samples taken from pet food that included raw chicken, raw chicken products, and live chickens. The detection of 142 chicken isolates from 76 establishments suggested that the outbreak was linked to multiple producers of chicken products.

The S. Infantis strain involved in the outbreak was first identified by FSIS’ National Antimicrobial Resistance Monitoring System (NARMS) in 2014 during routine surveillance as a strain with significant antimicrobial resistance (AMR). CDC also conducted AMR testing on S. Infantis bacteria isolated from case patients in the outbreak investigation and found that the strain was resistant to multiple antibiotics. Furthermore, over 90 percent of S. Infantis isolates from chicken were MDR. After the outbreak investigation was closed, CDC and FSIS classified the S. Infantis strain as “persistent,” and CDC continues to monitor the strain.

FSIS states that, because whole genome sequencing (WGS) was not fully implemented at the time of the 2018–2019 S. Infantis outbreak, it was not used to identify cases during the outbreak investigation; however, WGS was later used to confirm that the S. Infantis strain in question differs from other S. Infantis strains found in chicken samples. The agency is exploring ways to better track and promptly alert stakeholders of persistent pathogen strains that are novel or have not yet been associated with a specific food vehicle.

FSIS, which has recently made concerted efforts to reduce the number of salmonellosis cases caused by chicken products, urges the poultry industry to focus on decreasing Salmonella contamination across the supply chain, including at pre-harvest. The agency also asks its public health partners to work closely with local, state, and federal agencies to detect and investigate outbreaks, as well as to email FoodborneDiseaseReports@usda.gov to alert the agency when FSIS-regulated products may be involved in an outbreak.