Physician opinion: Foods that use fermentation, chemicals (vinegar, salt, sugar), bacteria, fungi, yeast, etc., in their production are not "spoiled", they are "processed", and include many regional specialties found less palatable by many in the U.S., except alcohols.
Spoilage refers more to when foods become inedible due to either excessive growth of added processing organisms (think three week-old Camembert), the accumulation of pathogenic populations, or their toxic by-products, or dehydration due to poor storage. Generally, the by-products of intentionally added organisms are not harmful, else we wouldn't use them, but the ammonia in the cheese is too much (and sets off explosive detectors in airports !, as I found out).Pathogens are organisms, or their by-products, harmful to humans.
There are several routes to illness from food:
1) Food can be contaminated in its production with highly virulent organisms which grow well even in small amounts (hepatitis A, typhoid, cholera) and point out the need to avoid employing carriers of these, and to practice good hand washing. No amount of proper storage prevents these.
2)Food can be contaminated in its production cycle with less virulent organisms which can then survive stomach acid and grow in the intestines and produce illness. Washing of foodstuffs (E. coli) and full cooking to bactericidal temperatures (Salmonella) reduces the chance of illness, as does cold storage to decrease the numbers of these bacteria to which a consumer is exposed. The immune system can deal with smaller numbers of these contaminants. Immune-compromised or immune-immature persons (children) do less well here, hence the instructions to fully cook eggs for children.
3) Food can be stored poorly such that less virulent pathogens grow to a population size that makes illness highly likely. Where food is already inhabited by an added organism, such as yoghurt, the waste products of the organism tend to suppress other organisms, and thus make spoilage less of an issue, hence the use of the method to prolong storage, historically. But, in other foods, if bacteria are present (and they are in the air constantly), warm storage will cause overgrowth. If poor preparation methods are used (cutting vegetables on meat boards, etc.), then the chance of Salmonella overgrowth is high. Keep surfaces and tools clean and separated! Richer foods, larger surface area (i.e. chopped meat), exposure to air-borne organisms, moisture and warmth combine to support bacterial growth, so closed, cool, dry, unchopped storage is good practice.
4) When storage conditions allow bacterial growth, two methods of illness occur. First, a direct pathogen grows to numbers too high for the body to cope with, and ingestion leads to growth in the intestines. This method usually appears as an illness after a couple of days, when the pathogen, say Salmonella, either invades the tissues or produces a toxin responsible for a symptom (diarrhea, etc.). Illness is more rapid dependent on the amount of ingestion.
5) Much food poisoning, however, is due to an indirect method: the organism produces a toxin as it grows in the "stored" food, and ingestion results in a rapid illness as the toxin is absorbed, often in the stomach. This type accounts for the '30-90 minutes after eating' illnesses, frequently caused by Staphylococci found on human skin, and not deactivated by heating. Again, prep methods are usually at fault, worsened by warm storage.
6) It is not often possible to determine whether food is contaminated as above, because some pathogenic organisms, and toxins, produce no obvious markers detectable by humans. But, if there is spoilage due to a non-harmful organism, this is obviously a sign that harmful things could also be present, and thus the food is better avoided, no?
7) Hepatitis B and C are communicated by blood-to-blood contact, not oral ingestion. And, hepC causes cancer in the liver through prolonged infection leading to scar tissue which transforms into cancer after 25 years or so, with some help from host-viral interaction, as far as we know.
8) Most molds are harmless, but high concentrations taste bad, even on cheese. Peanut mold is not, as it produces aflatoxin. There are plenty of other things that grow on food, such as slime molds, which are disgusting to look at, but not harmful. Even so, they are a marker for spoilage.
I cut mold off of cheese because I can't bear to waste it. I prefer fresher stuff, tho. I store everything I can fit into the fridge as this retards oxidation, which tastes bad, but is not harmful per se. Think olive oil.
The long and short of it is, know your food cycle.