While no one can debate the benefits of good hygiene, bacteria, viruses and parasites have to come from somewhere. Individuals infected with Giardia sp. are picking it up from somewhere; most likely source is the water.
It is possible a partner is infected and passing the Giardia sp. along to others due to poor hygiene via fecal contamination - oral route of exposure. However, I would think the water is still the most likely culprit, despite the test results, which may not be sensitive enough to detect low-level contamination.
WARNING & DISCLAIMER:
SELECT AND USE OUTDOORS AND SURVIVAL EQUIPMENT, SUPPLIES AND TECHNIQUES AT YOUR OWN RISK. Information posted
on this forum is not reviewed for accuracy and may not be reliable, use at your own risk. Please
review the full WARNING & DISCLAIMER about information on this
site.