Yorkies vomiting and diarrhea two weeks

Question
Two of my dogs, one a yorkie and one a cavi-fox had diarrhea and vomiting. The cavi-fox stopped after a couple of days. The one yorkie is now on her third week. She has some bloody but mostly liquid stool. For a week it had a grit in it. Our vet said after testing twice there are no parasites and no worms. So we went on to a RX dog food for low residue. Now another of my yorkies tonight had very bloody / mucus stools that I am scared. I don't know what to think and am worried about my dogs. Any opinion is welcome. I am going to take to the view tomorrow and insist on more test but could use some other input

Answer
Sounds like some type of contagious gastroenteritis caused by a virus or bacteria. Is there a possibility of some type of toxin exposure, perhaps something they all got into without you knowing? Are they currently on medication to control the diarrhea such as metronidazole? One suggestion I would have for your vet is to run a fecal culture on one of the dogs who is having diarrhea. Fecal cultures look for abnormal bacteria in the stool like Salmonella, Shigella and Campylobacter. If there is a bacterium causing the diarrhea, it can be treated with an appropriate antibiotic based on the sensitivity results of the test.

Dr. G.