If infected by E. Coli how much blood would be in the stool?

Answer 1

There is quite a range, from no blood to grossly visible bright red blood in the stool.

The variability arises for a number of reasons. First is that E. coli infections lead to bloody stools because some strains of E. coli produce toxins that damage the lining of the bowel and lead to hemorrhage (bleeding). Not all strains of E. coli produce such toxins, so not all are associated with hemorrhagic diarrhea.

Another reason for the variability is that even if infected with a strain of E. coli that leads to bloody stools, the degree to which the toxin damages the lining of the bowel is variable. Some individuals are able to mount a successful immune response against the bacteria, so that it cannot damage the bowel lining enough to produce bloody stools. Others' immune responses may suppress E. coli's damage to the extent that stools are bloody, but not visibly so (this is called occult, or hidden, blood).

(By the way, all humans naturally contain E. coli in the colon; it is considered part of the normal flora of the colon. This relationship is considered colonization, not infection, and should not be thought of as a disease process. However, as we've seen above, there are different strains of E. coli out there. The strains found in the body are generally nonpathogenic strains, meaning they are not invasive and do not generally produce toxins.)