Your shelter staff bring you an 8-week-old puppy surrendered…
Your shelter staff bring you an 8-week-old puppy surrendered 3 days ago. The puppy is lethargic, with pale mucus membranes, 10% dehydration, and has reported vomiting and bloody diarrhea. Yesterday, you euthanized two other puppies in the litter with similar signs. You run a test for parvovirus, which comes up negative. How do you interpret this, and what epidemiologic principle guides this interpretation?