Interesting....Fish and Sweet Potato is usually a food used for dogs with allergys. The Super5 mix Chicken or Lamb is much more widely sold. Maybe ask your pet store if they will get it. If they are ordering from that company in the first place there is no reason not to get a different food in the same line.
Giardia is a bacteria that dogs and humans can contract as well,from many things, usually water contamination. Think: People drinking the water in Mexico.
My Vet perscribed Metronidazole to cover Giardia or other types of bacterial overgrowth two 250mg caps twice a day. A heavy dose for a dog that didn't show Giardia on tests, but thats what it took.