Giardiasis

What Is It?

Giardiasis is an intestinal illness caused by infection with the parasite Giardia lamblia, which lives in contaminated water. Although the illness most frequently occurs in developing countries, giardiasis is also one of the most common causes of waterborne illness in the United States. In developing countries, more than 20 percent of the population may be affected, while in the United States are, the disease affects between 1 percent and 6 percent of the population.

G. lamblia parasites are found in the feces of infected people. A person can become infected with G. lamblia by:

• Drinking water that has been contaminated with the parasite (usually by contact with sewage)
• Eating fruits or vegetables that have been washed in contaminated water
• Touching feces from an infected person
• Touching objects soiled with feces
• Having direct contact with an infected person or animal

G. lamblia can survive in cold, chlorinated water for up to two months, and outbreaks have occurred in municipal water supplies.

People at greatest risk of giardiasis include:

• Children in day-care centers and their families
• Day-care workers
• Travelers to developing countries
• Campers who drink unprocessed water
• Homosexual men (because of anal sex)

Children are three times more likely to develop giardiasis than adults. It is possible that the human body develops some immunity to the parasite over time.

Symptoms

When giardiasis is widespread in a particular population, such as in a developing country, up to two-thirds of people infected with the organism do not have any symptoms. When symptoms occur, they typically start one to three weeks after exposure and include:

• The sudden onset of watery diarrhea
• Abdominal cramping
• Bloating
• Nausea
• Gas

Because G. lamblia interferes with the body's ability to absorb fats, the stools have a greater fat content, causing them to float and be foul-smelling. Less common symptoms include vomiting, low-grade fever and loss of appetite. If the infection lasts a long time, it can result in weight loss and fatigue.

Diagnosis

Your doctor will ask you about your travel history, whether you might have had contact with contaminated water during camping or hiking, and whether your home has well water. If the patient is a child who attends day care, the doctor will inquire about any recent outbreaks of diarrhea at the day-care center. He or she also will review the patient's symptoms.