Giardiasis, an intestinal illness, is caused by a microscopic parasite called Giardia lamblia . In 2008, there were 840 cases reported among New York City residents (rate of 10.2 cases per 100,000 persons).
Anyone can get giardiasis. However, it tends to occur more often in people residing in institutional settings, diaper-aged children in day care centers, child care workers, parents of infected children, foreign travelers, and individuals who drink improperly treated surface water (such as from lakes, rivers, or streams) or who swim in contaminated water. Men who have sex with men may also be at increased risk of contracting giardiasis.
The parasite is passed in the stool (feces) of an infected person or animal. When it is outside the body, it is protected by an outer shell, and can survive in the environment for long periods of time. It may contaminate soil, water, food or surfaces. People become infected by swallowing the parasite. Person-to-person transmission may occur in day care centers or other settings where hand-washing practices are poor. Sexual practices in which the mouth or hand comes into contact with a partner's anus or stool may result in spread.
Giardia has been found in infected people (with or without symptoms) and wild and domestic animals. The beaver has gained attention as a potential source of Giardia contamination of lakes, reservoirs, and streams, but human fecal wastes may be just as important.
People exposed to giardia may experience mild or severe diarrhea, abdominal cramps, bloating, and fatigue. In some instances, there may be no symptoms at all. Fever is rarely present. Occasionally, chronic diarrhea may develop over several weeks or months, with significant weight loss. In otherwise healthy persons, symptoms may last 2 to 6 weeks.
The symptoms may appear from 3 to 25 days after exposure, but usually within 10 days.
The carrier stage generally lasts from a few weeks to a few months. Treatment with specific antibiotics may shorten the carrier stage.
Diagnosis is made by examining the stool under a microscope or by using special detection tests for Giardia . Sometimes, several stool samples obtained on different days are necessary, since the number of Giardia parasites shed in the stool varies from day to day.
Anti-infective drugs such as metronidazole, tinidazole, or nitazoxanide are often prescribed by doctors to treat giardiasis. Drug resistance or relapse may occur with any drug. Some individuals may recover on their own without medication. Although Giardia can infect all people, young children and pregnant women may be more susceptible to the dehydration caused by diarrhea and should drink plenty of fluids while ill.
Since the Giardia parasite is passed in the stool, people with active diarrhea who are unable to control their bowel habits (for example, infants, young children, and certain disabled individuals) may need to be excluded from group settings where they present a risk to others. Most infected people may return to work or school when their stools become formed as long as they wash their hands thoroughly after using the toilet. Food handlers, certain health care workers, children in day care, pre-kindergarten or kindergarten, and employees in day care, pre-kindergarten and kindergarten must obtain approval from the Health Department before returning to their routine activities, even if they are not having diarrhea. This requires follow-up stool testing to be sure that they are no longer infectious.
The most important preventive measures include:
Practice good hygiene.
Avoid water that may be contaminated.
Avoid food that may be contaminated.
Take extra care when traveling.
Protect yourself and others.
Last updated December 2009.