system
Given the following post, respond as if you're commenting on Reddit:
human
Why do people get sick from eating contaminated food? Wouldn't the bacteria/virus be broken up by stomach acid?
gpt
The capacity of microbes to survive the acidic environment of the stomach is largely dependent upon a few variables:  

\-The microbial load:  The number of organisms accompanying the food bolus.  The more organisms there are, the greater the likelihood that at least a few will successfully pass through the stomach and in to the small intestine.

\-Time:  Food can pass through the stomach relatively quickly depending upon a few factors. It takes time for the acid concentration of the stomach to do what it does.  Sometimes food (and, therefore, microbes), simply pass through too quickly.

\-Adaptive mechanisms: Many microbes have adaptive mechanisms that protect against low pH. There is a long list of pathogenic microbes for which this is the case, but this also applies to microbes that are part of our normal microbiome and do not necessarily share a pathogenic relationship with us.

\-pH fluctuation:  The stomach isn't always at pH-2.  When food empties in to the stomach, the pH can rise as high as pH-6 depending on the particular materials being digested.  It's also important to recognize that, while the pH of solution can be low, the surface of food contents in the stomach can have a micro-environment that is relatively high-pH.

So while the normally low pH of stomach contents (pH 1-2) is often deleterious to a great many microbes, there is a wide array of conditions that ultimately allow microbes to pass through the stomach and in to the intestines, which is the primary site of infection for most food-borne infectious organisms.