October 30, 2019

CDC, public health and regulatory officials in several states, and the U.S. Food and Drug Administration (FDA)external icon Center for Veterinary Medicine investigated a multistate outbreak of multidrug-resistant human Salmonella infections linked to contact with pig ear pet treats. Salmonella strains included were Cerro, Derby, London, Infantis, Newport, Rissen, and I 4,[5],12:i:-.

Public health investigators used the PulseNet system to identify illnesses that may have been part of this outbreak. PulseNet is the national subtyping network of public health and food regulatory agency laboratories coordinated by CDC. DNA fingerprinting is performed on Salmonella bacteria isolated from ill people by using a standardized laboratory and data analysis method called whole genome sequencing (WGS). CDC PulseNet manages a national database of these sequences that are used to identify possible outbreaks. WGS gives investigators detailed information about the bacteria causing illness. In this investigation, WGS showed that bacteria isolated from ill people were closely related genetically. This means that people in this outbreak were more likely to share a common source of infection.

A total of 154 people infected with the outbreak strains of Salmonella were reported from 34 states. A list of the states and the number of cases in each can be found on the Map of Reported Cases page.

Illnesses started on dates ranging from June 10, 2015, to September 13, 2019. Ill people ranged in age from less than 1 year to 90 years, with a median age of 40 years. Seventy (45%) ill people were female. Of 133 ill people with information available, 35 (26%) were hospitalized. No deaths were reported.

Whole genome sequencing (WGS) was conducted to identify any predicted antibiotic resistance in 110 isolates from ill people and 102 isolates from pig ear treat samples. A total of 164 isolates had predicted antibiotic resistance or decreased susceptibility to one or more of the following antibiotics: amoxicillin-clavulanic acid (<1% of 164 isolates), ampicillin (53%), azithromycin (<1%), cefoxitin (<1%), ceftriaxone (<1%), chloramphenicol (33%), ciprofloxacin (50%), fosfomycin (2%), gentamicin (27%), kanamycin (2%), nalidixic acid (26%), streptomycin (33%), sulfisoxazole (30%), tetracycline (58%), and trimethoprim-sulfamethoxazole (27%). No antibiotic resistance was predicted for 48 (23%) isolates. Testing of 13 clinical isolates using standard antibiotic susceptibility testing methods by CDC’s National Antimicrobial Resistance Monitoring System (NARMS) laboratory provided comparable results (fosfomycin and kanamycin were not tested by this method). If antibiotics were needed, infections related to this outbreak may have been difficult to treat with some commonly recommended antibiotics, and may have required a different antibiotic choice.

Investigation of the Outbreak

Epidemiologic, laboratory, and traceback evidence indicated that contact with pig ear pet treats was the likely source of this outbreak.

In interviews, ill people answered questions about a variety of exposures, including animal and pet food contact in the week before they became ill. Of 128 ill people, 107 (84%) reported contact with a dog before getting sick. Of 94 people with available information, 62 (66%) reported contact with pig ear treats or with dogs who were fed pig ear treats. Both of these proportions were significantly higher than the results from a survey pdf icon[PDF – 787 KB] of healthy people who reported contact with dogs (61%) or handling dog treats (16%), such as pig ear treats, in the week before interview.

Testing of pig ear treats identified the outbreak strains of Salmonella in 135 samples. Some of the pig ear treats were imported from Argentina, Brazil, and Colombia. Some product labels indicated that the pig ear treats were irradiated. When properly conducted, the irradiation process should kill any Salmonella present on the pig ear treats. Finding Salmonella in products labeled as irradiated indicate they may not have been irradiated, they were not effectively irradiated, or there was another issue that caused Salmonella contamination. FDA  continues to investigate the manufacturing process and has posted answersexternal icon to frequently asked questions from members of the pig ear pet supply chain (manufacturers, suppliers, importers, distributors, retailers) regarding Salmonella control in these products.

Several firms recalledexternal icon pig ear treats during the investigation because they were contaminated with Salmonella. No single supplier, distributor, or common brand of pig ear treats was identified.

As of October 30, 2019, the outbreak appears to be over.