Giardia lamblia

Giardia infection is an intestinal infection marked by abdominal cramps, bloating, nausea and bouts of watery diarrhea. Giardia infection is caused by a microscopic parasite that is found worldwide, especially in areas with poor sanitation and unsafe water.
Giardia infection (giardiasis) is one of the most common causes of waterborne disease in the United States. The parasites are found in backcountry streams and lakes, but also in municipal water supplies, swimming pools, whirlpool spas and wells. Giardia infection can be transmitted through food and person-to-person contact.
Giardia infections usually clear up within six weeks. But you may have intestinal problems long after the parasites are gone. Several drugs are generally effective against giardia parasites, but not everyone responds to them. Prevention is your best defense.