Stomach flu symptoms and signs of food poisoning can be almost indistinguishable.
Infectious diarrhea can be caused by a virus or by bacteria. Regardless of the classification of the pathogen causing the acute gastroenteritis the results will be very much the same.
You will feel pretty sick, will likely have a fever and also experience nausea, diarrhea, and maybe even stomach cramps.
An intestinal virus can picked up from food or from other surfaces. Bacterial food poisoning however, occurs because the bacteria actually live and grow on the food eventually causing the food to spoil or go rotten. While nobody would want to eat rotting food that smells bad, most bacterial food poisoning occurs before the food has reached that rotten stage so even though the bacteria are there and multiplying and growing it might not be obvious to you and the others at the banquet table.
So how can you tell if the vomiting and diarrhea you are experiencing are stomach flu symptoms or food poisoning? Well most of the time you cannot tell just by the symptoms. It would only be possible to tell for sure by testing the stool and this is rarely done.
Most often an intestinal virus or even a bacterial food poisoning will be a shortlived illness and you will recover within a few days. It may only be necessary to see a physician if the symptoms do not resolve and the illness progressively worsens. This can indicate that there is a rare serious bacteria involved, or that your body is just not able to fully recover perhaps because of dehydration or some other underlying condition that has worsened as a result of the infectious diarrhea.
The one symptom that is more typical of a bacterial food poisoning than a viral gastroenteritis is bloody diarrhea. While it is possible for this to occur in infants and toddlers with acute gastroenteritis, is it not typical. On the other hand, bloody diarrhea may be common for many of the bacterial infections from food poisoning and this characteristic of diarrhea stools distinguishes several of the more serious types of infectious diarrhea such as that caused by E coli.
If you have diarrhea and can see bright red blood in it, then that would be a reason to go see the doctor. However, most cases of food poisoning and intestinal flu are not serious enough to warrant visits to a physician and will subside on their own within a few days of becoming sick.
So even though stomach flu symptoms may not be distinguishable from food poisoning, there may be other ways to tell if you picked up an intestinal virus or ate some rotten food. In my experience however, people who have fever, nausea, vomiting, stomach cramps and diarrhea aren’t usually interested in leaving the house to get these kinds of details attended to. You might want to just go to bed and let the illness run its course.
These two types of illnesses however, can differentiated by observing the way that they spread. If you know someone who has been sick with vomiting and diarrhea, and then you become sick, and then a day or so later someone else in the family comes down with similar symptoms, it is likely an intestinal virus that has been transmitted from person to person. The analogy would be like a domino trail with each domino falling individually.
If however, you have been at a social gathering where food was served and a large number of people become ill all with the same symptoms, at the same time, then this is likely food poisoning. The analogy here would be a tower of dominoes crashing all at once instead of one by one.
So the signs of stomach flu and symptoms of food poisoning are pretty much the same with the possible exception of bloody diarrhea. However, you should be able to determine whether an intestinal virus or a bacteria was the source of your torment by the nature of the spread of the illness.
The only other definitive way to tell the difference would be to have a stool sample examined and honestly by the time you are well enough to do that the illness will be over anyway.