Food safety sampling is often in the spotlight when contaminated products cause illness or injury. Consumers question if the product was tested and, if so, why the testing did not detect the pathogen, toxin, or other hazard responsible. The unfortunate reality is that, although many food products are tested for hazards, they test negative, and yet high-profile recalls or outbreaks still occur in those commodities.
Why does this happen? In many bulk products, hazard contamination is not uniformly distributed, and it occurs at low levels when it does occur. Even those clusters of low-level contamination may present a risk of a recall or an outbreak. Yet, such clusters of low-level contamination make it difficult to take what are typically relatively small product grab samples used for testing in a way that would capture the hazard if it were present. This is not a "needle in a haystack" problem—those are easy to solve with a metal detector. Instead, it is a microscopic bacterium on a few produce leaves or a few nanograms of toxin on some corn kernels in a large bin.