Enteric Disease Outbreaks Associated with Animal Contact — Animal Contact Outbreak Surveillance System, United States, 2009–2021
Authors: Taylor Eisenstein, Marisa Wong, Grace Vahey, Ariana Perez Toepfer, Brigette Gleason, Katharine Benedict
Journal: MMWR Surveillance Summaries (2025)

An estimated 450,000 enteric illnesses, 5,000 hospitalizations, and 76 deaths associated with animal contact occur each year in the United States. Enteric illnesses are diseases that affect the stomach or intestines and cause symptoms, such as diarrhea, nausea, or vomiting, and are typically transmitted from animals to humans through the fecal-oral route. Humans might encounter animal feces or bodily fluids through contact with the animal itself, the animal's environment, or the animal's food or water. Although outbreak-associated illnesses account for a small subset of all enteric illnesses linked to animal contact, data obtained from outbreak surveillance offer insights into the underlying epidemiologic factors contributing to illnesses, including the pathogens, animals, pathogen-animal category pairs, and settings of outbreaks associated with animal contact. 2009-2021. The Animal Contact Outbreak Surveillance System (ACOSS) was launched in 2009 in conjunction with the National Outbreak Reporting System (NORS), a web-based platform that includes reports of foodborne and waterborne outbreaks as well as enteric disease outbreaks transmitted by contact with environmental sources, infected persons or animals, or unknown modes. ACOSS encompasses animal contact outbreaks that are reported to CDC through NORS. Local, state, and territorial health departments voluntarily report animal contact outbreaks, which are defined as two or more enteric illnesses associated with a common animal source. Outbreaks can involve single or multiple states; CDC staff typically report multistate outbreaks on behalf of state and territorial health departments. ACOSS defines an animal source as an animal (including domestic and wild animals); an animal's feces or bodily fluids (except milk and other fluids consumed as food, which are defined as foodborne sources); an animal's fur, hair, feathers, scales, or skin; an animal's food; or an animal's environment, which includes places in which it lives and roams. During 2009-2021, a total of 557 animal contact outbreaks of enteric disease were reported in the United States through ACOSS, accounting for 14,377 illnesses, 2,656 hospitalizations, and 22 deaths. Exposures were reported in all 50 states, Washington, DC, and Puerto Rico. During the period there were 393 single-state outbreaks and 164 multistate outbreaks. Although multistate outbreaks comprised 29% of all outbreaks reported through ACOSS, they accounted for 80% of illnesses, 88% of hospitalizations, and 82% of deaths. Among 474 outbreaks with a confirmed single etiology, Salmonella was the most common cause of outbreaks (248 outbreaks [52%]); these outbreaks accounted for the most outbreak-associated illnesses (11,822 [85%]), hospitalizations (2,393 [91%]), and deaths (17 [77%]). Cryptosporidium (108 outbreaks [23%]) was the second leading cause of confirmed, single etiology outbreaks, followed by Escherichia coli (63 [13%]) and Campylobacter (52 [11%]). The most common exposure locations among outbreaks with a single location reported were private home (168 [40%]) and farm or dairy (89 [21%]). Among 467 outbreaks for which an animal source could be attributed to a single animal category, ruminants (171 [37%]) were the most implicated animal category (with 75% of ruminant outbreaks attributed to cattle), followed by poultry (155 [33%]) and turtles (39 [12%]). Poultry were associated with the most outbreak-associated illnesses (9,095 [66% of illnesses resulting from outbreaks attributed to a single animal category]), hospitalizations (1,804 [70%]), and deaths (15 [83%]). Most outbreaks (130 [84% of all poultry outbreaks]) attributed to poultry had private home reported as at least one of the exposure locations (i.e., backyard poultry) and were responsible for nearly all poultry-associated illnesses (8,897 [98%]). The most common confirmed pathogen-animal pair was Salmonella and poultry (132 outbreaks), followed by Cryptosporidium and ruminants (88), and Salmonella and turtles (37). Salmonella and poultry accounted for the highest number of outbreak-associated illnesses (8,965), hospitalizations (1,790), and deaths (15). Animal contact outbreaks of enteric disease reported through ACOSS provide insights into the animals and etiologies causing outbreak-associated enteric illnesses as well as other outbreak characteristics, such as settings in which outbreaks occur. These findings can guide public health actions, developed in collaboration with specific populations (e.g., backyard poultry owners) and including interventions tailored to settings, such as private homes and farms or dairies, that are more commonly associated with animal contact outbreaks. The high proportion of outbreaks occurring in private homes identifies a potential gap in proper hygiene and enteric disease prevention knowledge among animal owners, including owners of backyard poultry, which might be considered by owners to be pets rather than livestock. Settings and populations linked to ruminants, poultry, and turtles (particularly cattle, backyard poultry, and small turtles, respectively) are important targets for public health interventions because of the high number of outbreaks and outbreak-associated illnesses associated with these animal sources. Furthermore, the disproportionate impact of multistate outbreaks reiterates the importance of a collaborative national response but also might reflect limited resources to investigate or report animal contact outbreaks at state and local levels. Public health partners should continue to report animal contact outbreaks through ACOSS to inform evidence-based interventions tailored to specific animals, pathogens, populations, and settings. Strengthening the capacity of local, state, and territorial health departments to investigate and report animal contact outbreaks is critical to improving surveillance of animal contact outbreaks. Close collaboration between state, local, and Federal public health and agricultural partners nationwide is also key in investigating and responding to multistate outbreaks. An integrated One Health approach that leverages the expertise of animal, environmental, and public health partners can facilitate successful public health interventions aimed at preventing animal contact outbreaks.