Giardia infection (giardiasis) is an intestinal infection caused by a microscopic parasite that’s found worldwide, especially in areas with poor sanitation and unsafe water. Giardia infection is marked by abdominal cramps, bloating, nausea and bouts of watery diarrhea.
Giardia infection is a waterborne infection and can be caused by parasites found in backcountry streams and lakes, as well as in municipal water supplies, swimming pools, whirlpool spas and wells. Giardia infection can also be transmitted through food and person-to-person contact.
Giardia infections usually clear up within a few 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.
Giardia parasites live in the intestines of people and animals. Before the microscopic parasites are passed in stool, they become encased within hard shells called cysts, which allows them to survive outside the intestines for months. Once inside a host, the cysts dissolve and the parasites are released.
Infection occurs when you accidentally ingest the parasites. This can occur by swallowing contaminated water, by eating contaminated food or through person-to-person contact.
Swallowing contaminated water
The most common way to become infected with giardia is after swallowing contaminated water.
Giardia parasites are found in lakes, ponds, rivers and streams worldwide, as well as in municipal water supplies, wells, cisterns, swimming pools, water parks and spas. Ground and surface water can become contaminated from agricultural runoff, wastewater discharge or animal feces. Children in diapers and people with diarrhea may accidentally contaminate pools and spas.
Eating contaminated food
Giardia parasites can be transmitted through food — either because food handlers with giardiasis don’t wash their hands thoroughly or because raw produce is irrigated or washed with contaminated water. Because cooking food kills giardia, food is a less common source of infection than water is, especially in industrialized countries.
You can contract giardiasis if your hands become contaminated with fecal matter — parents changing a child’s diapers are especially at risk. So are child care workers and children in child care centers, where outbreaks are increasingly common. The giardia parasite can also spread through anal sex.
Some people with giardia infection never develop signs or symptoms but still carry the parasite and can spread it to others through their stool. For those who do get sick, signs and symptoms usually appear one to two weeks after exposure and may include:
- Watery, sometimes foul-smelling diarrhea that may alternate with soft, greasy stools
- Fatigue or malaise
- Abdominal cramps and bloating
- Belching gas with a bad taste
- Weight loss
Signs and symptoms of giardia infection usually last two to four weeks, but in some people they last longer or recur.
When to see a doctor
Call your doctor if you have loose stools, abdominal bloating and nausea lasting more than a week, or if you become dehydrated. Be sure to tell your doctor if you’re at risk of giardia infection — that is, you have a child in child care, you’ve recently traveled to an area in which you know giardia infection is present, or you’ve swallowed water from a lake or stream.