The reason, he explained, is that many people rinse off their cutting board rather than thoroughly washing it.
"You have potential pathogens when you're dealing with food," said Tierno.
He recommended preparing a solution of a quart of water and "a jigger of bleach" and then wiping down food preparation surfaces before making anything on those areas of the kitchen.
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Cari Nierenberg and Joseph Brownstein contributed to this report.