Hello,
Thanks for the query to H.C.M. Forum.
One group is there and passing
black stool.
Bacteria is there , but chances of bacterial infection is less.
Bacterial infection usually causes
fever etc, in your case ,such type of history is not there.
Now here is one point ,as you are in a group and you must have shared same food or eatables.
These are few foods which causes black stool as,
1 Some iron food or
iron supplements ( millet is one , such type of food)
2 blueberries ,
3black
liquorice (licorice) sweet fruit.
So please recapitulate your memory, think , what you consumed in group, result and reason , you will find out.
Hope you have find your answer.
If further any question I will help.
Good luck all of you.
Dr. HET