Blastocystis species carriage

Bowen, 2016Byrne, 2015de Boer, 2020Mathison, 2019Roberts, 2014Stensvold, 2016

Historically, Blastocystis species was detected only by faecal microscopy. With transition to multiplex polymerase chain reaction (PCR) faecal testing, which is more sensitive, it has become evident that carriage of Blastocystis species is much more common than previously thought.Microbiology Advisory Committee The Royal College of Pathologists of Australasia (RCPA), 2023 However, the pathogenicity of these organisms has not been established¹.

Identification of Blastocystis species in a faecal sample should be interpreted with care – Blastocystis species are commonly detected in asymptomatic individuals, and when Blastocystis species are identified in a symptomatic patient, symptoms are more likely to have an alternative cause.

In patients with persistent abdominal symptoms (eg abdominal pain, diarrhoea) and Blastocystis species carriage, it is important to investigate for other causes, including irritable bowel syndrome, inflammatory bowel disease, malabsorption syndromes, colon cancer, Clostridioides difficile (formerly known as Clostridium difficile) infection, enteric bacterial infection, HIV-related opportunistic infections, Tropheryma whipplei infection (Whipple disease). Consider referral to a gastroenterologist.

The use of antimicrobial therapy for Blastocystis species is controversial and is not supported by good quality evidence. However, in symptomatic patients in whom other causes have been excluded, treatment may be considered – seek advice from an infectious diseases physician.

Repeat courses of antibiotics and retesting are not indicated.