ARCHIVED - An international outbreak of human Salmonellosis associated with animal-derived pet treats - Canada and Washington State, 2005

 

Canada Communicable Disease Report

1 July 2006

Volume 32
Number 13

Introduction

In 2004-2005, contact with Salmonella-contaminated pet treats of beef and seafood origin resulted in human Salmonella Thompson infections in the State of Washington (WA) in the United States (USA) and in Western Canada. This is the third published report of an outbreak of human illness associated with pet treats in North America, the first in the USA. This report describes the investigation of the international outbreak and provides recommendations on how to reduce the risk Salmonella-contaminated pet treats pose to humans. Public health practitioners should consider pet treats a potential source for Salmonella transmission.

Case 1

In February 2005, a 26-year-old man in Alberta (AB), Canada, presented with diarrheal illness. Stool culture yielded S. Thompson. The patient fed his dog beef pet treats a few days before the onset of his illness. The dog was asymptomatic. A package of the same brand of pet treats fed to the dog was purchased and submitted for testing. The treats yielded S. Thompson, S. Cerro and S. Meleagridis. The S. Thompson isolates from the patient and treats were indistinguishable (i.e., the outbreak strain) by pulsed-field gel electrophoresis (PFGE). The treats were packaged and distributed by a British Columbia (BC) manufacturing plant, but records were inadequate to determine where the treats had been produced.

Case 2

In February 2005, a 37-year-old woman in BC presented with diarrheal illness. Stool culture yielded S. Thompson. The patient fed her dog salmon pet treats a few days before the onset of the patient's illness. The dog also had a diarrheal illness, but specimens were not collected. The remaining pet treats were collected from the patient's house for testing. The treats yielded S. Thompson. Isolates of S.Thompson from the patient and treats were indistinguishable from each other and from the outbreak strain by PFGE. The salmon treats originated from a WA manufacturing plant. The treats were imported into Canada, labeled and distributed for sale in BC and AB by the same BC manufacturing plant identified in case 1.

Case 3

In March 2005, an 81-year-old woman inWA presented with diarrheal illness, fever, and vomiting. The patient was hospitalized and stool culture yielded S. Thompson indistinguishable from the outbreak strain by PFGE. The patient purchased and fed beef pet treats to her dog, but did not recall touching the pet treats prior to the onset of her illness. The patient had frequent contact with her dog, but reported no recent illness in the dog. The remaining treats were collected from the patient's house for testing. The treats yielded S. Thompson. The treats originated from and were packaged by theWA manufacturing plant that was the source of the treats in case 2.

Additional Cases

Six additional human cases of S. Thompson (three in BC, two in WA and one in AB), indistinguishable by PFGE from the outbreak strain, were identified by retrospective case finding. Five of the six additional patients were interviewed. Three (60%) of them were exposed to pet treats from the WA or the BC manufacturing plants. The two other cases had pet dogs. Stool culture from an asymptomatic dog yielded S. Thompson indistinguishable from the outbreak strain by PFGE.

Source Investigation

The BC and WA manufacturing plants were investigated by authorities. Both manufacturers processed frozen raw beef into pet treats for cats and dogs by thawing the materials, cutting them into the desired shapes and sizes, dehydrating them, and then packaging and/or wrapping the finished products for distribution. The manufacturers in BC and WA received frozen raw beef parts from slaughter houses in Canada and the USA, respectively. The WA manufacturer also received frozen raw salmon from aWA seafood company, and frozen raw shrimp from two seafood companies - one located in WA and the other in Rhode Island. Although the pet treats were dehydrated, the dehydration temperatures were not high enough to kill bacteria that may have been present. No other bacterial kill step, such as irradiation, was used during the processing. Production code dates, lot numbers and location of plants were not recorded on the finished product packaging. The BC manufacturing plant received some of its processed beef treats, and all of its processed salmon and shrimp treats from the WA manufacturing plant.

Cultures of shrimp, salmon and beef pet treats manufactured at theWA plant and collected at the BC plant by Canadian authorities and cultures of salmon treats collected at theWA plant by USA authorities yielded S. Thompson indistinguishable by PFGE from the outbreak strain. The salmon treats contained up to 80,000 CFU of Salmonella per gram. Pet treats from the BC and WA plants also contained other Salmonella serotypes including S. Montevideo, S. Newport, S. Give, S. Meleagridis, S. Cerro, S. Muenster, S. Agona, and S. Anatum. Both manufacturing companies issued voluntary recalls of the implicated products in June 2005.

Editorial - CDC Atlanta

In 2004, there were 5,085 laboratory-confirmed cases of human Salmonella infections in Canada, and 35,661 laboratory-confirmed cases in the USA(1,2). Studies in the USA have shown that for each laboratory-confirmed case of Salmonella infection, there are 38 Salmonella infections in the community, indicating that over one million people in Canada and the USA may be infected with Salmonella each year(3). Although salmonellosis is generally a self-limiting infection, it can result in serious illness in more vulnerable populations such as the very young, the elderly, and immunocompromised persons. Most human Salmonella infections are acquired by handling or consuming contaminated food products, particularly foods of animal origin. Infections are also acquired by direct and indirect contact with farm animals, reptiles, chicks, and occasionally companion animals. Infected animals usually shed Salmonella in their feces. Humans can become infected when contaminated food, hands, or other objects are placed in the mouth; therefore, hand washing is critical to prevent Salmonella infection following contact with animals. In recent years, an increasing variety of animal by-products, such as pig ears, have become available for purchase as animal-derived pet treats for companion animals. Animal-derived pet treats have been associated with previous outbreaks of human Salmonella infection in Canada. In 1999, contaminated pig ear pet treats were confirmed as the source of an outbreak of human S. Infantis infections in several provinces(4,5). In 2002, contaminated pet treats imported from Texas were associated with human S. Newport infections in Calgary(6). Follow-up investigations in Canada and the USA indicated that pet treats are frequently contaminated with Salmonella. In Canada, following the 1999 outbreak, Salmonella was isolated from 48 (51%) of 94 samples of pig ear pet treats purchased from retail stores in Alberta(5). In theUSA, Salmonella, including S. Infantis, was isolated from 65 (41%) of 158 samples of pig ear and other animal-derived pet treats purchased from retail stores in 1999-2000(7). The S. Infantis isolates from the patients in Canada and the pet treats in the USA were indistinguishable by PFGE.

Detecting and controlling the transmission of Salmonella via pet treats poses several challenges(8). Animal-derived pet treats are often contaminated with Salmonella, and the dehydration procedure used to make pet treats may not be effective at eliminating Salmonella. Aside from direct contact with contaminated pet treats, transmission of Salmonella to humans may also occur indirectly through the pets. Pets consuming contaminated treats may be colonized with Salmonella but asymptomatic, thus becoming unknown sources of contamination in the household. Families with young children or elderly household members who feed their pets animal-derived pet treats should be particularly careful as Salmonella infection in these age groups is often more severe.

In Canada, pet treats are not regulated, but the Canadian Food Inspection Agency has used the Animal Health Act to encourage or enforce product recall. The Public Health Agency of Canada and the Pet Industry Joint Advisory Council are collaborating to improve product safety.

In the USA, pet treats are regulated by the Food and Drug Administration (FDA). Salmonella-contaminated pet treats are considered adulterated under the Federal Food, Drug, and Cosmetic Act. After the 1999 Canadian outbreak, the FDA encouraged industry to take voluntary steps to ensure the absence of Salmonella in pet treats. The American Pet Products Manufacturers Association published “Guidelines for the Manufacturing of Natural Pet Treats for Pets” to educate its members(9). The FDA initiated annual nationwide testing of pet treats for Salmonella. Because the prevalence of Salmonella in pet treats in the USA has remained constant over time, the FDA will broaden its use of enforcement actions to ensure compliance with the Act.

Pet treat manufacturers, retailers, consumers, and public health authorities should be aware of the potential for animal-derived pet treats to serve as a source of Salmonella for human disease. Public health authorities should routinely consider this possibility during their investigations of cases or outbreaks of human salmonellosis.

Recommendations

  1. People should always wash their hands thoroughly with soap and water after handling pet treats and their pets.

  2. People at increased risk for infection or serious complications of salmonellosis (e.g., children aged < 5 years, elderly and immunocompromised people) should avoid contact with animal-derived pet treats.

  3. Pet store owners, health-care providers, and veterinarians should provide information to pet owners about the potential health risks of animal-derived pet treats, and prevention of salmonellosis.

  4. Pet treat manufacturers should implement a bacterial kill step in the processing of pet treats, such as heat treatment or irradiation.

Acknowledgements

We would like to thank our public health and laboratory colleagues from Alberta, British Columbia and Washington State and the CFIA and FDA for their assistance in this investigation.

References

  1. Notifiable Diseases Reporting System, Surveillance and Risk Assessment Division, Centre for Infectious Disease Prevention and Control, Public Health Agency of Canada. 2006.

  2. CDC. Salmonella surveillance: Annual summary, 2004. Atlanta, Georgia: US Department of Health and Human Services, CDC, 2005.

  3. Voetsch AC, Van Gilder TJ, Angulo FJ et al. FoodNet estimate of the burden of illness caused by nontyphoidal Salmonella infections in the United States. Clin Inf Dis 2004;38:S127-34.

  4. LCDC. Human health risk from exposure to natural dog treats. CCDR 2000;26(6):41-2.

  5. Clark C, Cunningham J, Ahmed R et al. Characterization of Salmonella associated with pig ear dog treats in Canada. J Clin Microbiol 2001;39:3962-68.

  6. Pitout JDD, Reisbig MD, Mulvey M et al. Association between handling of pet treats and infection with Salmonella enterica serotype Newport expressing the AmpC ß-Lactamase, CMY-2. J Clin Microbiol 2003; 39:538-42.

  7. White DG, Datta A, McDermott P et al. Antimicrobial susceptibility and genetic relatedness of Salmonella serovars isolated from animal-derived dog treats in the USA. J Antimicro Chem 2003;52:860-3.

  8. Finlay R, Reid-Smith R, Weese JS. Human health implications of Salmonella-contaminated natural pet treats and raw pet food. Clin Infect Dis 2006;42:686-91.

  9. American Pet Products Manufacturers Association, Inc. Guidelines for the Manufacturing of Natural Pet Treats. Available at: http://www.appma.org/ Accessed: March 20, 2006.

Source: Shendra Brisdon, CPHI(C), CD Public Health Inspector, Fraser Health Authority; Eleni Galanis, MD, MPH, FRCPC, Physician Epidemiologist, British Columbia Centre for Disease Control, Vancouver, BC, Canada; Romulo Colindres, MD, MPH, Epidemic Intelligence Service Officer, Foodborne and Diarrheal Diseases Branch, Centers for Disease Control and Prevention, Atlanta GA; Larry Crowe, CPHI(C), Enteric Investigations, Calgary Health Region; Lorraine McIntyre, Gastroenteritis Outbreak Coordinator, Supervisor, Food Poisoning, Environmental Services, Laboratory Services, British Columbia Centre for Disease Control; Rebecca Baer, MPH, Epidemiologist,Communicable Disease Epidemiology, Washington State Department of Health; Laura MacDougall, MSc, Surveillance Epidemiologist, British Columbia Centre for Disease Control; Lynn Wilcott, BSc, P. Ag. Food Safety Specialist, British Columbia Center for Disease Control; Larry Gustafson, MD, MHSc, Medical Health Officer, Fraser Health Authority; Ana Paccagnella, BSc, RT, Supervisor, Enteric Bacteriology, British Columbia Centre for Disease Control; Linda Chui, PhD, Molecular Program Leader, Provincial Laboratory for Public Health (Microbiology), Alberta, Canada; Doug Everett, CPHI(C), Manager, Environmental Public Health, Alberta Health and Wellness; Diane MacDonald, MHSc, Foodborne, Waterborne and Zoonotic Infections Division, Public Health Agency of Canada; Andrea Ellis, DVM, Foodborne, Waterborne and Zoonotic Infections Division, Public Health Agency of Canada; M Leslie, DVM, MPH, Public Health Veterinarian, Communicable Disease Epidemiology, Washington State Department of Health; Christine E Keys, Microbiologist, Food and Drug Administration, Center for Food Safety and Applied Nutrition; Henry Ekperigin, DVM, MPVM, PhD, Food & Drug Administration, Center for Veterinary Medicine; Mark L Collins, Consumer Safety Officer, Food and Drug Administration, Seattle District Office; A Drake, MPH, Epidemiologist, Communicable Disease Control, Epidemiology & Immunization Section, Public Health - Seattle & King County; J Koepsell, MS, Epidemiologist, Communicable Disease Control, Epidemiology & Immunization Section, Public Health - Seattle & King County; C DeBolt, RN, MPH, Epidemiologist, Communicable Disease Control, Epidemiology & Immunization Section, Public Health - Seattle & King County; S McKeirnan, RN, MPH, Epidemiology Response Coordinator, Communicable Disease Control, Epidemiology & Immunization Section, Public Health - Seattle & King County; J Duchin, MD, Chief, Communicable Disease Control, Epidemiology & Immunization Section, Public Health - Seattle & King County; Janelle M. Johnson, Microbiologist, Food and Drug Administration, Pacific Regional Laboratory Northwest; Doris E Farmer, Microbiologist, Food and Drug Administration, Denver District Laboratory; Fred Angulo, DVM, PhD, Foodborne and Diarrheal Diseases Branch, Centers for Disease Control and Prevention, Atlanta, Georgia.

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