What is the actual probability of food poisoning with food left unrefrigerated overnight? [closed]

I'm not sure how answerable this is, as kitchens vary so much.

A clean, cool kitchen will be very different to a steamy hot, dirty one, in terms of both likelihood of contamination and growth of pathogens after the food is contaminated. Some pathogens are also almost ubiquitous. Homes may be cleaner than they used to be, but in temperate parts of the world they're also warmer.

It doesn't of course help that the guidance is almost all written for cases where for is being provided for the unsuspecting public (including individuals at greater risk) rather than in the home.

And then it depends on the food as well. Some support the growth of particularly bad species particularly well (e.g. cooked rice), others tend to spoil in detectable ways before they're colonised by nasties (many dairy products and actually bread).

From my experience I can say that the risk from food left out is really rather small compared to other sources of food poisoning - but a sample size of one is no use. Even if it's not a threat to your overall health, food poisoning is very unpleasant so it's worth a little effort to avoid it by cooling hot food quite quickly and chilling it. I sometimes forget stuff that starts too hot to put in the fridge, but don't waste it, and that's how I know the probability has to be low. That's not a recommendation, far from it.

There are a few things to consider here: As others have pointed out, it depends on the conditions under which the food is prepared. There is also the consideration of the types of food and the cooking styles (e.g. are the foods being cured at all, or just cooked?), and the practices around storing and re-heating the food (or not).

Several studies have been done, which show that around 80% of food poisoning cases are caused by home cooking (not too surprising really, most people eat at home most of the time), so the risks are real. If you look at the CDC for the US, they estimate that 48 million people will get food poisoning each year (in 2011). That's about 15% of the population of 300 million or so. Now not all those cases are from foods cooked at home, and far fewer are from foods stored overnight on the counter after cooking, which seems to be the question that OP is asking.

I have been unable to find any data that specifically deals with foods left out overnight after cooking; most of the literature deals with general food preparation and storage practices. In general it seems that people perceive the risk to be low, believe that it won't happen to them and lack knowledge of food preparation procedures. These along with a bunch of socio-economic factors (including gender, education, wealth, etc) all tie in to the risk and the practices used in the kitchen, where people on the lower end of each scale (gender included - men: wash your hands!) tend to fare worse in food safety and consequent illnesses.

Now back to numbers: in the US, of the 48 million, some 128,000 (0.04% of population) will be hospitalized, and around 3000 (0.00096% - 9.6 per million) die, so even if you do get sick, the risks are very low of an adverse event.

The best thing you can do is educate yourself and learn the safe practices - wash your hands, clean surfaces well before and after preparation, don't mix raw with cooked (meats especially). Cook to safe temperatures, store appropriately, cover and chill foods not being eaten immediately.

There is not "the" risk. The best microbiologists can do is to come up with different models, each with different assumptions. And since we are talking about a complex system, the predictions of the models will vary wildly with even tiny differences in initial conditions.

In fact, this is not even what microbiologists do. They create models that answer the question "How much food poisoning would occur, given that people do their best to follow current guidelines". I am not aware of them being public, but even if they were, they are not suited for calculating what you asked, just like a weather model that is suitable for predicting the weather on Earth tomorrow is not suited for predicting the weather on Venus tomorrow. You can see this excellent answer for an idea what goes into the current models. Millions of dollars and decades of research progress have been spent to get the information about what happens when the strict guidelines are in place. Nobody has invested the money and career time in searching for a definitive answer what happens when the guidelines are not followed in random ways.

So the best you can do is to go with your own gut feeling based on your empirical observations of people not following the guidelines. This again depends on food habits - for example, in an old question similar to yours, but confined to a single risk, I found sources stating that in Asian populations eating traditionally prepared fish, there is 20% prevalence of fish borne parasite infections. When I grew up, my family and our friends also didn't follow strict guidelines, and I think that in our conditions, the risk of symptomatic illness was below 1 percent per day of eating a mix of refrigerated and unrefrigerated food.

Also, even with such information, you won't be able to make an informed decision. The problem is that humans are very bad with dealing wiht risk numbers in their heads, and if forced to, are subject to a host of biases. The brain "rounds" very small risks to "this won't happen anyway", as long as one hasn't observed them happening, and to "this is terrible, we have to make lots of effort to protect ourselves" if it has happened. And after years on this site, I can assure you that this is what happens with attitudes towards food safety too. Even when risk equations sound sensible, you are as incapable of putting a number on your own risk aversion (to put it into the equation) as seeing your own blind spot. If you are interested, go deeper into Kahnemann and Tversky's research on risk.

So while I understand where you are coming from and why you want to do it this way, it is impossible. You either trust the FDA and follow their guidelines, or you just live with unknown risk. Making an informed decision is not an option, since the information asked for doesn't exist.

The question you're asking is almost impossible to answer, because it strongly depends on the kind of food and how it has been prepared. Your nose is often a good indicator: if it smells bad, there's a good chance it is bad (though the opposite is not necessarily equally valid)

I would also like to point out that bacteria are not the only thing that can cause food to become unsafe to eat. Food can be unsafe to eat because of: - bacteria - viruses - parasites - toxins

Particularly the last one is interesting in my opinion, because while the others may in principle be killed by sufficiently heating your food, toxins may still remain even after you've heated your food.