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 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.
Not everyone with giardiasis has symptoms, but they can still spread the disease.
Symptoms can appear between 1 and 3 weeks after infection.
They may include:
- A slight fever
- Watery or soft stools and constipation
- Foul-smelling diarrhea and gas
- Abdominal bloating, pain and cramps
- Belching and halitosis, or foul-smelling breath
- Heartburn and indigestion
- Loss of appetite and weight loss
- A general feeling of being unwell
Stools usually eventually become greasy but do not contain blood.
Diarrhea can lead to dehydration. If water loss is severe, it can become serious, especially for infants. It is important to consume plenty of fluids, preferably water.
Symptoms normally improve within 2–6 weeks, but this may take longer. Medications can help speed up recovery.
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 parasite cysts. 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.
Giardiasis Risk factors
The giardia parasite is a very common intestinal parasite. Although anyone can pick up giardia parasites, some people are especially at risk:
- Children. Giardia infection is far more common in children than it is in adults. Children are more likely to come in contact with feces, especially if they wear diapers, are toilet training or spend time in a child care center. People who live or work with small children also are at higher risk of developing giardia infection.
- People without access to safe drinking water. Giardiasis is rampant wherever sanitation is inadequate or water isn’t safe to drink. You’re at risk if you travel to places where giardiasis is common, especially if you aren’t careful about what you eat and drink. The risk is greatest in rural or wilderness areas.
- People who have anal sex. Having anal sex without using a condom puts you at an increased risk of giardia infection, as well as sexually transmitted infections.
Giardia infection is almost never fatal in industrialized countries, but it can cause lingering symptoms and serious complications, especially in infants and children. The most common complications include:
- Dehydration. Often a result of severe diarrhea, dehydration occurs when the body doesn’t have enough water to carry out its normal functions.
- Failure to thrive. Chronic diarrhea from giardia infection can lead to malnutrition and harm children’s physical and mental development.
- Lactose intolerance. Many people with giardia infection develop lactose intolerance — the inability to properly digest milk sugar. The problem may persist long after the infection has cleared.
A doctor will take a stool sample and send it to a lab to check for Giardia cysts.
Sometimes, they will ask for several samples, because a person does not expel cysts every time they use the bathroom.
If the results do not show giardia, but the person has symptoms that seem to suggest giardia, the doctor may carry out further tests.
This may include endoscopy and possibly a biopsy from the small intestine.
No drug or vaccine can prevent giardia infection. But commonsense precautions can go a long way toward reducing the chances that you’ll become infected or spread the infection to others.
- Wash your hands. This is the simplest and best way to prevent most kinds of infection. Wash your hands after using the toilet or changing diapers and before eating or preparing food. When soap and water aren’t available, alcohol-based sanitizers are an option. However, alcohol-based sanitizers are not effective in destroying the cyst form of giardia that survives in the environment.
- Purify wilderness water. Avoid drinking untreated water from shallow wells, lakes, rivers, springs, ponds, and streams unless you filter it or boil it for at least 10 minutes at 158 F (70 C) first.
- Keep your mouth closed. Try not to swallow water when swimming in pools, lakes or streams.
- Use bottled water. When traveling to parts of the world where the water supply is likely to be unsafe, drink and brush your teeth with bottled water that you open yourself. Don’t use ice, and avoid raw fruits and vegetables, even those you peel yourself.
- Practice safer sex. If you engage in anal sex, use a condom every time. Avoid oral-anal sex unless you’re fully protected.
Metronidazole (Flagyl) is a drug that is effective for treating giardiasis. A doctor will prescribe the drug and advise about dosage.
Side effects are rare, but they may include:
- Dark or cloudy urine
Metronidazole may interfere with alcohol dehydrogenase, an enzyme that breaks down alcohol. For this reason, a person should avoid alcohol during treatment.
Other possible medications
Other options include:
- Tinidazole (Fasigyn)
- Nitazoxanide (Alinia)
Frequently Asked Questions
What is giardiasis?
Giardiasis (GEE-ar-DYE-ah-sis) is an intestinal illness caused by a parasite called Giardia lamblia. It is a commonly reported cause of diarrheal illness in New Jersey. G. lamblia can be found in humans and other animals, such as beavers, thus a common name once used for giardiasis was “beaver fever.”
Who gets giardiasis?
Anyone can get giardiasis, but it is frequently found in people living in institutional settings, in child care settings, and travelers to areas with poor sanitary conditions. People who drink untreated surface water, such as ponds, lakes, and streams, are at increased risk of getting giardiasis.
How can I get Giardia?
Giardia is passed through the feces of an infected animal or person. Infection in humans most often occurs from drinking contaminated water or eating contaminated food. People living in areas without access to safe drinking water are particularly susceptible. Infection can also occur if your hands become contaminated with fecal matter; this makes parents and caretakers of young children particularly at risk. One of the challenges of Giardia is that the parasite can survive outside of a host for weeks or months by forming a hard cyst. This means that the parasite can still spread even if there is no sign of active infection.
How do I know if I have Giardia?
In many people, Giardia is asymptomatic, meaning there are no obvious signs of infection. When symptoms do occur, it is typically within one to three weeks of infection. The most common symptoms are diarrhea, fatigue, abdominal cramps, bloating and gas, and nausea. Because these symptoms are often chalked up to other causes, however, many people do not suspect a Giardia Elisa infection. If left untreated, Giardia will eventually lead to more acute symptoms, including bloody diarrhea, weight loss, and dehydration.
If you or your child experience a bout of diarrhea lasting more than a day or two, contact your doctor immediately. Your doctor will collect a stool sample and perform either a fecal flotation test to look for Giardia cysts in the sample or an antigen test to more precisely detect the presence of antigens in the sample. Some versions of these antigen tests need to be sent out to labs for analysis, while others produce rapid results and can be read by your doctor within 10-15 minutes.
How is Giardia typically treated?
For people who do not present with symptoms of Giardia, treatment for Giardia infection is often not necessary unless the infected person is likely to spread the disease to other people (for example, if the infected person is a young child or works in a child care center). If symptoms do persist or progress, your doctor will most likely prescribe a course of anti-protozoal and/or antibiotic medication to clear the Giardia infection from your system. For severe cases, people may also need to be treated for dehydration.
How can I protect myself and my family against giardia?
As with most other common parasitic infections, the prevention of Giardia infection is key. The easiest way to prevent Giardia infection is to wash your hands thoroughly and ensure proper hand-washing techniques in children. Avoid drinking untreated water, and use clean water to wash any foods that are to be eaten raw. In areas with poor sanitation, use bottled water or water filters to reduce your risk of infection.
In addition, always pick up your pet’s feces immediately using gloves or a bag over your hand. If the infection does occur, it is also important to disinfect household objects that may have come into contact with Giardia cysts. A combination of 1-2 cups of bleach in 1 gallon of water should be used on bleach-safe surfaces such as toilets and countertops.
What types of Giardia tests are there?
Giardia is tested using a fecal flotation test or an antigen test. The different types of antigen tests include lateral flow tests, such as the IVD Giardia Stool Antigen Detection Lateral Flow test kit, which can be done at your doctor’s office; ELISA tests, such as the IVD Giardia and Giardia/Cryptosporidium Stool Antigen Detection Microwell ELISA test kits; and direct immunofluorescence assays, like the IVD Cryptosporidium/Giardia Human Fecal Direct Immunofluorescence Antigen Detection Kit. Both of these latter kits require fecal samples to be sent to a reference laboratory.
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