Gut Illness Outbreaks From Animal Contact, 2009–2021: Backyard Poultry, Cattle and Turtles

Enteric illnesses affect the stomach or intestines and cause symptoms such as diarrhea, nausea or vomiting. Many spread from animals to people by the fecal–oral route: people meet animal feces or body fluids by touching the animal, its surroundings, or its food or water. A 2012 estimate put illnesses from animal contact in the United States at 450,000 a year, with 5,000 hospitalizations and 76 deaths; about 14% of those illnesses are estimated to be part of outbreaks.

An estimated 57%–70% of U.S. households own at least one pet. Contact with animals helps mental, social and physical health, but Salmonella from backyard poultry and reptiles such as bearded dragons and small turtles has repeatedly caused multistate outbreaks.

This CDC report counts the outbreaks reported for 2009–2021.

How outbreaks are counted

• ACOSS, the Animal Contact Outbreak Surveillance System, was set up by CDC in 2009 inside the National Outbreak Reporting System (NORS), the web platform that also takes reports of foodborne, waterborne and person-to-person outbreaks.
• Health departments report voluntarily; CDC usually reports multistate outbreaks.
• An outbreak is two or more enteric illnesses linked to a common animal source: the animal itself; its feces or body fluids (except milk and other fluids eaten as food, which count as foodborne); its fur, hair, feathers, scales or skin; its food; or its environment — coops, cages, aquariums, farms, schools, petting zoos, pet stores.
• Backyard poultry outbreaks are those involving poultry where at least one place of exposure was a private home.
• In an outbreak tied to pet food or treats, the implicated animal is the one the food was meant for.

The report covers finalized reports as of January 18, 2023, whose first illness began between January 1, 2009 and December 31, 2021.

The totals

• Outbreaks per year: median 45, range 21–62.
• Single-state outbreaks were reported by 44 states; median 4 ill per outbreak (range 2–205), and 11% of the ill were hospitalized.
• Multistate exposures happened in all 50 states, Washington, DC, and Puerto Rico; median 40.5 ill per outbreak (range 3–848), 20% hospitalized, and a median of 16.5 states per outbreak (range 2–49).
• Overall, 18% of the ill were hospitalized — from 7% in 2010 to 22% in 2015.

Enteric disease outbreaks and illnesses from animal contact, by year, 2009–2021: 557 outbreaks, 14,377 illnesses. Figure from CDC's report.

The germs

474 outbreaks had a single confirmed cause, accounting for 13,941 illnesses, 2,623 hospitalizations and 22 deaths.

• Salmonella and Cryptosporidium together caused 12,735 (91%) of these illnesses; Salmonella and STEC caused 2,531 (96%) of the hospitalizations and all 22 deaths.
• Salmonella outbreaks had the highest hospitalization rate: 20%.
• Counting suspected causes too, bacteria caused 405 single-cause outbreaks (75%), 13,160 illnesses (93%), 2,593 hospitalizations (98%) and all 22 deaths; the rest were parasites.
• The most common Salmonella serotype was Typhimurium (47 outbreaks); the most common STEC serogroup was O157 (44).

Where people caught it

545 outbreaks named at least one place of exposure. 417 named just one:

128 outbreaks named several places, and they accounted for 55% of illnesses. The pair named together most often was an agricultural feed store and a private home (68 outbreaks); farms or dairies, pet stores, animal shelters or sanctuaries, camps and petting zoos also appeared.

The animals

An animal was named in 505 outbreaks; in 467, it could be pinned to one kind of animal, and those accounted for 13,806 illnesses.

• Cattle were behind 128 of the ruminant outbreaks (75%) and 1,136 of their illnesses (70%); in 89 ruminant outbreaks (52%), a farm or dairy was a place of exposure.
• Poultry caused 1,804 of 2,563 hospitalizations (70%) and 15 of the 18 deaths in outbreaks pinned to one kind of animal.
• Backyard poultry: 130 of the 155 poultry outbreaks (84%) named a private home, and they caused 8,897 of the poultry illnesses (98%).
• Small turtles (shell under 4 inches) caused 24 of the turtle outbreaks (62%) and 1,143 of their illnesses (86%); 35 turtle outbreaks (90%) named a private home.

Germ and animal together

One death each came from Salmonella and turtles, STEC and goats and sheep, and Salmonella and hedgehogs. The remaining deaths came from STEC outbreaks with no animal named, or several that could not be pinned to one kind.

Pet food and treats

13 outbreaks (2%) were linked to pet food and treats: 459 illnesses, 72 hospitalizations and one death.

The homemade-food outbreak was also tied to live poultry: one patient had made cat food at home from frozen rabbit bought online and game hen.

Multistate outbreaks

Multistate outbreaks were 29% of all outbreaks but caused 11,442 illnesses (80%), 2,333 hospitalizations (88%) and 18 deaths (82%). Poultry were named in 105 (64%) and caused 8,803 of their illnesses (77%); turtles were named in 28 (17%) and caused 1,262.

In other NORS reporting, multistate outbreaks have been a much smaller share. Animal contact outbreaks tend to be more often multistate and longer than foodborne ones, partly because food can be recalled and pets usually cannot — and many of these germs are a normal part of healthy animals' gut flora. The small number of single-state outbreaks may also reflect limited resources in local, state and territorial health departments.

What the authors conclude

• Backyard poultry caused the most outbreaks and illnesses. Poultry have long been known to carry Salmonella, and backyard flock outbreaks have risen with flocks' popularity — perhaps partly because whole-genome sequencing finds more of them. Owners, especially new ones, need clear prevention messages; many treat their birds as pets rather than livestock.
• Turtles ranked third for outbreaks and illnesses despite federal and state laws that ban or limit selling small turtles. Young turtles shed more Salmonella than adults, especially after handling or shipping, and children handle them and often lack good handwashing habits. Illegal sales go on because transient vendors and online sellers are hard to track; states and localities can pass their own laws, for example limiting turtles around children.
• Homes were the most common setting, pointing to a gap in hygiene knowledge among owners of backyard poultry, turtles and other animals.
• In public settings, the National Association of State Public Health Veterinarians recommends separating animal and non-animal areas, handwashing stations, and educating visitors and staff. Farm workers need protective equipment and handwashing.
• Health departments should keep reporting, and their capacity to investigate should be strengthened; multistate outbreaks need federal, state and local public health and agriculture partners working closely together, in a One Health approach joining human, animal and environmental health.

Limits

• Reports can change at any time, and voluntary reporting likely undercounts outbreaks.
• Health departments may define animal contact, especially indirect contact, differently.
• There are no confirmation guidelines specific to animal contact outbreaks, as there are for foodborne ones.

Since 2023, the NORS form asks what role the animal played (pet, backyard livestock or poultry, exhibit animal) and which interventions were used.

Sources

Based on Eisenstein T, Wong M, Vahey G, Perez Toepfer A, Gleason B, Benedict K, "Enteric Disease Outbreaks Associated with Animal Contact — Animal Contact Outbreak Surveillance System, United States, 2009–2021," MMWR Surveillance Summaries, volume 74, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The source gives turtles' share of single-animal outbreaks as both 12% and 8%, poultry's share of those deaths as both 83% and 68%, turtles' share of multistate illnesses as 17% against counts that do not match it, single-location outbreaks' share of illnesses as both 45% and 44%, and multistate illnesses as both 80% and "approximately half"; the disputed figures are left out, and the 80% kept here is the one its table supports. Its animal table labels goats "ovine" and sheep "caprine", the reverse of the usual terms, so the split between the two is not given.