This article snapshot was given to me by the head veterinarian of dog law in Harrisburg, PA dept of Agriculture.
Your pup may test positive multiple times. Look at the pup’s symptoms. Is he lethargic? Not eating? Have runny poo with blood? (Soft poo is fine). The giardia test is an immunoassay test. If the pup has been exposed in the past he will continue to test positive after infection resolution for up to a month. It is so common that your pup will likely test positive atleast once in his lifetime.
We have found that probiotics, drinking clean water, healthy immunity along with successful medications treat the condition.
We treat with flagyl and toltrazuril. Your vet may also prescribe panacur (fendabendazole). Once your pup is over the bug he will be immune for life.