What it is:

• Single-celled animal, a protozoan and intestinal parasite, also known as Giardia intestinalis.
• Two forms:
  • Trophozite, or active form, is teardrop-shaped and attaches to the intestinal wall. It is released from the cyst form (below) to cause disease. Trophozite cannot live long outside the body.
  • Cyst, or inactive form, is produced by the trophozite in the intestine. Has a highly resistant “shell” which allows it to live outside the body and infect others. When ingested, it is activated by stomach acid and produces disease-causing trophozites.
• Size: Cyst can be as small as 7 microns.

Occurrence:

• Worldwide.
• Cysts found in:
  • Feces of infected humans and animals.
  • Water: Natural water supplies; water in swimming pools, hot tubs, spas and water parks; ice made from contaminated water.
  • Other: Uncooked food, surfaces contaminated with feces.

Health Effects:

• Causes giardiasis, also called “beaver fever” or “traveler’s diarrhea.” Very common: Up to 2.5 million cases occur annually in the United States. Potentially life-threatening to infants. Some adults develop immunity or never show symptoms.
• Symptoms: Begin one to two weeks after becoming infected: diarrhea, stomach or abdominal cramps, nausea. Can lead to weight loss and dehydration.
• Treatment: Selected prescription drugs.

Regulation:

• Giardia is a primary contaminant under the Safe Drinking Water Act. US Environmental Protection Agency (EPA) sets a maximum contaminant level goal (MCLG) of zero.
• Under federal Surface Water Treatment Rule enforced by EPA, public water supplies must show removal or inactivation of Giardia to at least the three-log (99.9 percent) level.

Water treatment:

• Filtration that removes all particles 4 microns or larger — particularly reverse osmosis, nanofiltration and ultrafiltration. Recommended: Filters that remove all particles 1 micron or larger and are certified for cyst removal under NSF/ANSI standards.
• Ultraviolet
• Carbon filtration
• Ozonation
• Note: Routine chlorination not recommended; shock chlorination can be effective.