Blastocystis hominis is a species of one of the most common human intestinal organisms. Many people with Blastocystis hominis in their stools have no symptoms.  The organism is most likely transmitted via the faecal-oral route.  Good hygiene practices should be used to help prevent transmission.

Last updated: 01 November 2015

What is Blastocystis hominis?

Blastocystis hominis is a species of one of the most common human intestinal organisms. Blastocystis species are found in people throughout the world and higher numbers are reported in developing countries. Blastocystis has also been found in a wide range of animals including mammals, birds and amphibians.

There is still debate about whether Blastocystis species really causes disease in humans, as the organism can be found in both well and unwell individuals. New research suggests that some types of Blastocystis may be more likely to be associated with symptoms.

What are the symptoms?

Many people with Blastocystis hominis in their stools have no symptoms at all. However, in those that do report symptoms, the most common ones are diarrhoea, abdominal pain and vomiting. Other reported symptoms are anal itching, weight loss, constipation and excess gas. However, such symptoms may be caused by other conditions, even if Blastocystis is found in the stools.

How is it spread?

It’s not certain how Blastocystis is spread. Given that the organism is found in the gastrointestinal tract, transmission is most likely to occur via the faecal-oral route. This means that infection might occur if you bring something to your mouth that has touched the faeces of a person infected with Blastocystis or if you swallow food or water contaminated with the organism.

Who is at risk?

Blastocystis is found in the intestines of many people, some without ever having symptoms.

Some studies have shown that people with poor immune systems have higher rates of identification of Blastocystis in their stools. People who travel to areas of poor sanitary condition are also more likely to have Blastocystis identified.

How is it prevented?

As Blastocystis seem to be more common in places with poor sanitation, it is important to practice good hand hygiene, especially after using the toilet and before handling food.

Some general precautionary measures that should be taken are:

  • Wash hands thoroughly using soap for at least 10 seconds and dry them with a clean towel after using the toilet, before preparing food and after handling nappies.
  • Avoid food or water that may be contaminated by sewage
  • Wash and peel all raw vegetables and fruits before eating
  • When travelling in countries where the water supply may be unsafe, avoid drinking unboiled tap water.

How is it diagnosed?

Diagnosis is based on symptoms and on finding the Blastocystis organism from a stool sample. It is also important to exclude other causes of a patient’s symptoms.

How is it treated?

Due to the uncertainty of whether this organism is a pathogen or not, it is difficult for doctors to decide whether to treat the infection.

There are medications available to treat Blastocystis infections. However, these are not always effective in relieving symptoms and it may be necessary for the doctor to look for other possible causes of a patient’s symptoms.

What is the public health response?

Blastocystis hominis is not a notifiable condition in New South Wales and there is no public health response required for individual infections.​

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