Editor's note: The following are excerpts from two presentations during the 2026 annual meeting of the American Association of Avian Pathologists.
David Ayala-Velastegui and Nikki Shariat, Poultry Diagnostic and Research Center, University of Georgia, USA, noted that almost 20% of salmonellosis cases are linked to consumption of undercooked, contaminated chicken. Salmonella prevalence in broiler-breeder flocks is significantly lower than in broilers, where typically approximately 85% of flocks are positive. Therefore, there is a need to understand how broiler flocks become colonized with Salmonella.
This study aimed to assess Salmonella serovar transmission across different stages of broiler production in six broiler complexes across four different states in the United States. Environmental samples were taken from breeder houses (n=53), hatcheries (n=45), and broiler houses immediately before chick placement (n=44) and seven days after placement (n=45) to determine whether Salmonella found in broilers is coming from prior stages or from resident Salmonella in the broiler house. Salmonella was cultured following the National Poultry Improvement Plan protocol. Serovar populations were determined by CRISPR-SeroSeq.
Approximately one quarter of pre-placement samples were Salmonella-positive, while after one week all broiler houses were positive. Important serovar-specific transmission dynamics were observed. The presence of serovars Enteritidis and Mbandaka in broiler-breeders and hatcheries indicate vertical transmission, while the Infantis serovar was only observed on broiler farms at 0 and 7 days, suggesting horizontal transmission and on-farm persistence from previous broiler flocks. Broiler flocks at 7-days have more complex Salmonella populations than found at the other three stages. Understanding transmission differences among different serovars will facilitate the application of broad Salmonella control strategies, as well as controls and surveillance targeted toward specific serovars to improve poultry food safety.
Decreased susceptibility to ciprofloxacin
Laura Ford, Centers for Disease Control and Prevention, and colleagues at the CDC, USDA, and FDA, observed that Salmonella Enteritidis is the most common cause of salmonellosis in humans in the US. In 2024, the National Antimicrobial Resistance Monitoring System (NARMS) reported a concerning increase in the number of Enteritidis isolates with decreased susceptibility to ciprofloxacin from ill humans and poultry. Ciprofloxacin is a first-line treatment for salmonellosis.
The researchers analyzed sequenced Enteritidis isolates from humans and poultry during 2013–2024 using data from the Centers for Disease Control and Prevention, the Food and Drug Administration, and the United States Department of Agriculture. Approximately 30% (19,447/65,052) of all Enteritidis isolates had decreased susceptibility to ciprofloxacin, caused by a GyrA(D87Y) mutation, and all the isolates constituted a single genetically related strain (SE65758-D87Y). SE65758-D87Y caused over 6,500 infections in humans in 2024, with an overall hospitalization rate of approximately 33%.
The 2013–2024 trends of SE65758-D87Y in poultry were coincident with the trends observed in human clinical illness. Human and poultry isolates were genetically indistinguishable. Leading sources of human SE65758-D87Y outbreaks included backyard poultry contact and consuming chicken or shell eggs. As fluoroquinolones have been banned for use in poultry in the United States since 2005, further research is needed to understand drivers of the emergence and predominance of this strain. Focused prevention strategies to contain further spread in poultry and humans should be considered.