Canadian researchers find C. difficile in retail meat

No proof of foodborne transmission yet

On the heels of a similar American finding, Canadian researchers have documented the presence of potentially disease-causing strains of Clostridium difficile in retail ground meat samples from grocery stores.

C. diff was isolated from 12 (20%) of 60 retail ground meat samples purchased over a 10-month period in 2005 in Ontario and Quebec Canada. Eleven isolates were toxigenic, and eight (67%) were classified as toxinotype III. "The human health implications of this finding are unclear, but with the virulence of toxinotype III strains further studies are required," the researchers noted.

The Canadian finding is similar to ongoing research being conducted at the University of Arizona in Tucson, where C. diff was detected in 28% of beef, 35% of the pork, and 10% of the turkey samples tested. Research and analysis is continuing, but the most disconcerting finding is that the C. diff strains detected in the United States included the highly toxigenic strain that has been linked to infections in hospitals and the community (ribotype 027).

"Both CDC and Canadian public health agencies are working together on this," reports Clifford McDonald, MD, a leading C. diff expert and medical epidemiologist in the division of health care quality promotion at the Centers for Disease Control and Prevention. "There is no evidence so far that it is transmitted by the food supply, but we are concerned because of its recent emergence in food producing animals and the fact that it can be cultured in retail meats. We are actively looking into this."

The foodborne theory is one of several under discussion as epidemiologists track increasing infections in the community by a pathogen normally acquired in the hospital. Noscomial C. diff typically spreads via the hands of health care workers from the contaminated environments of patients whose primary symptom often is diarrhea. However, the traditional picture is changing as C. diff threatens to arise independently in the community such as community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA).

Much of this change has been attributed to the emergence of one toxigenic strain, classified according to PCR as ribotype 027/toxinotype III and pulsed-field gel electrophoresis (PFGE) as NAP1, the Canadian researchers note. While they didn't precisely detect ribotype 027, they reported something only slightly less disconcerting. The most common ribotype, which accounted for eight (67%) of 12 isolates, was different from any ribotype previously identified in their laboratory among some 1,500 human and animal isolates. This ribotype, designated M31, had genes for toxins A, B and CDT; an 18-bp deletion in the tcdC gene and was toxinotype III.

These "toxinotype III strains have many similarities with PCR ribotype 027, an important cause of CDAD in humans," they noted. "PCR ribotype 027 strains produce all three toxins and have a mutated toxin regulatory gene, tcdC, which is thought to be associated with increased toxin production in vitro."

The presence of C. difficile spores in bovine feces indicates the potential for contamination of retail meat products, they surmised." Although contamination does not necessarily mean food borne transmission, the possibility of C. difficile being a food borne pathogen should be investigated," the concluded. ". . . The presence of meat-derived PCR ribotypes indistinguishable from human, bovine, and canine ribotypes further supports the potential risk for cross-transmission among species and suggests that ingestion of viable spores might occur. Although proper cooking of meat is emphasized for reducing the risk for foodborne disease, the fact that C. difficile is a spore-former complicates this issue because spores can survive in ground beef at recommended cooking temperatures (71°C), even when that temperature is maintained for 120 minutes."

Reference

  1. Rodriguez-Palacios A, Staempfli HR, Duffield T, et al. Clostridium difficile in retail ground meat, Canada. Emerg Infect Dis [serial on the Internet]. 2007 Mar [date cited]. Available from www.cdc.gov/EID/content/13/3/485.htm.