Two recent studies of bacteria on reusable plastic containers — both sponsored by corrugated carton groups — question the cleaning process used on RPCs before they enter the supply chain again.

RPC supplier IFCO and the Reusable Packaging Association has countered that no foodborne illness outbreak has been traced to RPCS.

Keith Warriner, professor of food safety at the University of Guelph in Ontario, Canada, said the study of RPCs — commissioned by the Canadian Corrugated and Containerboard Association — was an extension of one he performed in 2013. The first study tested 50 RPCs, the 2014 study involved 160 RPCs.

In the 2014 study, RPC samples from five Canadian packing facilities were pulled from different lots of trays that had been delivered on pallets wrapped with plastic film. Corrugated cartons from those facilities were not tested for comparison, Warriner said.

The study found that 13% of the RPCs tested positive for generic E. coli, but none tested positive for salmonella; 73% exceeded bacterial load levels, although that doesn’t mean they tested positive for E. coli, salmonella, listeria or other pathogens commonly associated with foodborne illness outbreaks.

“The results of the study have confirmed that a high proportion of RPCs are of poor sanitary status due to inadequate sanitation or post-cleaning contamination,” Warriner said in the study’s conclusion.

Trevor Suslow, produce safety specialist and plant pathologist at University of California-Davis, also conducted a recent study of RPCs, “Assessment of General RPC Cleanliness As Delivered for Use in Packing and Distribution of Fresh Produce.” Corrugated Delivers sponsored efforts to publicize the results and International Paper sponsored the testing.

Suslow said his research shows inconsistencies in the system for handling pooled RPCs. The difference between the Canadian study and Suslow’s is that his research tested RPCs with visible organic matter or residual produce material.

“The main takeaway from that is that we found, other than in a few cases across a few different weeks or pallet loads, the units that looked visually clean and dry had very similar viable or living microbial indicator counts compared to the ones we pulled apart for cause,” he said.