Allen Mozek, M.P.H., Supervising Food Inspector, New York State Department of Agriculture & Markets, writes in this contribution to barfblog.com that,

I find that food inspectors in all regulatory agencies have a tendency to confuse their inspection techniques with their investigative techniques. This results in lost evidence (primarily food samples) to prove the cause of a foodborne illness.

A little background…

The spirit of public health and food inspection is education and prevention. Food inspectors are allowed access without a warrant because they are looking for compliance, whereas police officers are denied access without a warrant because they are looking for evidence. This difference in emphasis on compliance versus evidence gathering reflects a difference in approaches. Evidence is gathered during routine inspection, but a food inspector’s initial expectations are compliance (or so says public health law).

Unfortunately, the daily emphasis on education and prevention creeps into investigations of foodborne disease. I say "creep" because I suggest that the habit of educating prevents inspectors from finding the evidence necessary to solve cases.

Once a case is reported, an inspector should be gathering evidence and
no longer educating at the expense of "showing your hand" or otherwise
reveal too much information. I think it’s about changing gears from an
inspection mentality to an investigation mentality — the two are very
different.