Trends in a Persistent Strain of Multidrug-Resistant Salmonella Infantis (REPJFX01) in Humans and Chickens - United States, 2010-2023.

Chicken is a major source of foodborne salmonellosis in the United States. The number of human illnesses and the prevalence in chicken of a multidrug-resistant strain of Salmonella enterica serotype Infantis called REPJFX01 have increased during the last decade. REPJFX01 isolates are often resistant to antibiotics used for treatment, including ampicillin, ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole. Using data from the U.S. Centers for Disease Control and Prevention's PulseNet system and the U.S. Department of Agriculture's Food Safety and Inspection Service during 2003-2023, we examined trends in REPJFX01 isolation from humans and chicken carcasses to assess whether they coincide. We used penalized B-spline generalized additive models to quantify trends in human infection burden and REPJFX01 prevalence on chicken carcasses. We used a time-lagged rank-order cross-correlation to characterize the association between the two-time series. A significant, increasing annual trend in the incidence of human infections and chicken carcass prevalence began in 2016. A 0-year lag on chicken carcass REPJFX01 prevalence maximized rank-order cross-correlation with REPJFX01 infection burden in humans. REPJFX01 trends in humans and chickens appear coincident (both occurring during the same time period), suggesting that chickens may be an important reservoir for REPJFX01. Efforts to prevent Salmonella contamination of chicken and strengthen safe handling and cooking of chicken should be prioritized.