Dysentery probably killed more soldiers in times past than being wounded. It's distinguished from the Norovirus in that it produces bloody diarrhea with mucus. It's usually caused by a bacterial infection of Shigella .
It might be the result of handling contaminated meat. A small nick of the digestive tract of the harvested animal may result in fecal contamination. This means that you've educated your hunters and whoever butchered the animal, and also cooked all meat WELL DONE. This is a collapse situation, and so you cannot be too careful with your meat preparations.
It can be mild, but all infection in a collapse must be taken seriously. It usually passes in three days, and as long as the person is isolated and cared for, then they'll probably be fine. If you were lucky enough to be around antibiotics, then it might be cured quickly.
The problem is that it takes several days to incubate, and by then you've become ill, and perhaps by then you've been preparing food for everyone. You don't have a way to culture the bacteria, and so you treat the person as if they have Shigella gastroenteritis based upon the symptoms and the relatively brief time period. The standard treatment is one of the following: “ampicillin, trimethoprim/sulfamethoxazole (also known as Bactrim or Septra), nalidixic acid and the fluoroquinolone, or ciprofloxacin. “
[link to textbookofbacteriology.net
An old Civil War remedy for treating this form of dysentery was persimmon syrup. Re-read the post I made about harvest persimmons and why it's something you want to preserve just in case.
[link to www.cw-chronicles.com
It could be amoebic dysentery though. This is often the result of drinking contaminated water. This is very likely if the sewage system has been infiltrated in a collapse, or because survivors are looking for water sources and have improperly cleaned what's been found.
Amoebic dysentery is very very serious. It lasts and lasts forever. The standard treatment is a first course of metronidazanole and then a course of diloxanide furoate.
If you don't have access to these medicines, while you may recover slowly over many months, you will continue to have the parasite in your system.
[link to www.webmd.boots.com