Is food safety a matter of presence or quantity? (of contaminants)

Question

When I cook at home, I tend to be hyper-sensitive to food safety. If I am handling raw meat, and the same hand merely grazes a serving dish, I consider it contaminated and may clean it. I try my best to keep part of my hands clean, always, to turn on the sink, so I can avoid the horrifying possibility of getting the faucet handles contaminated (in which case I would be doomed to forever-contamination, as every time I cleaned my hands I would have to touch the contaminated faucet to turn the water off). When I clean a cutting board after handing raw meat, I pay attention to ensuring that every part of the cutting board gets hit with the sponge, and I worry about missing a spot. When my housemate handles raw chicken and touches, well, anything, even a little bit, it really bothers me.

This style of management treats food safety as roughly binary: either the food / tool / dish "is" contaminated, and needs to be thoroughly cleaned (and your hands with it), or it "is not" contaminated, and you can do pretty much whatever you want with it. Lots of food safety resources encourage this style of thinking by using binary language. For example, this cooking.SE question references a bowl as "is contaminated"; and this this question and this foodsafety.gov article both take a non-binary viewpoint on risk of contamination, but still consider food either "contaminated" / "spoiled" or "safe".

Lately I've been wondering if this viewpoint is mistaken, and if my food safety habits are overkill. My understanding is that the primary concern of potentially-dangerous food is that it may be hosting harmful bacteria¹. It seems natural that bacteria is not a binary risk: one hundred individual E. Coli bacteria is probably a lot less of a concern than a billion, as I imagine the latter to be a much greater load on my immune system. Is it the same, then, with food safety?

Is the light touch of a contaminated hand against a serving dish not a concern, because the quantity of contaminants moved is going to be so low as to be negligible? (Assume no time / bad conditions for the bacteria to multiply) Or is the mere presence of contaminants enough to call for a cleaning?

Similarly, it feels common to me for someone (myself, friends, TV chefs, or otherwise) to put a steak into a pan, cook it, turn it, cook it, and take it out all with the same tongs. Is this dangerous?

If it is a matter of quantity, how can we distinguish between what's negligible and what's dangerous? How much contamination is too much?

Thank you

[¹]: Although there is also concern about toxins produced by bacteria, as mentioned here

Answer 1

Purely from a toxicological perspective, dosage is everything (for a given agent, of course). A very common way to express the risk of a toxic substance is in terms of a “dose-response curve,” which might allow you to read off, for example, for a dosage of d micrograms per kilogram of body mass, the probability of experiencing a given threshold toxic effect is p.

Analogously, when decontaminating, the keys are concentration (of your sanitizing substance) and… critically! … contact time. You have to give a decontaminant the chance to work its damage on the bad bugs, to accomplish things like denaturing their proteins and breaking their chemical bonds. Microbes have evolved to withstand some pretty rude affronts, so a quick “spray on and wipe off” is very seldom an effective technique.

If your intent is merely to remove contaminants, rather than to destroy them, then you care far less about contact time and more about the specific chemical interaction of the cleaning substance your using to dislodge and wash away the bugs.

Answer 2

There is, to some degree, a minimum dose of poison or infectious agent which is necessary to get you sick, and of course the severity of an illness can depend on the dose.

For cooking purposes, though, that’s rarely a useful piece of information. The relative dose of E. coli on a hastily rinsed cutting board versus a fully washed cutting board can be several orders of magnitude. It rarely matters what the exact minimum infectious dose is; a given cutting board is almost certainly either definitely clean, or definitely going to get you sick. Exponential growth, similarly, means that the range of “potentially safe” incubation times is often pretty narrow.

So, yes, the presence of contaminants is sufficient for one to assume the presence of sufficient contaminants. Exceptions should be made by experienced and disinterested microbiologists, not home cooks looking at the steak on the floor and considering some on-the-spot special pleading.