A cross-specialty push is underway to rein in detection and antibiotic treatment of two gut parasites whose role in gastrointestinal disease (IBS) remains under debate.

The group of specialist doctors – spanning pathology, gastroenterology and infectious diseases medicine –are campaigning to raise awareness of what they describe as unnecessary testing and treatment of Blastocystis species and Dientamoeba fragilis, which show up in about 20% of faecal polymerase chain reaction (PCR) tests since the highly sensitive tests became widely available in Australia in 2013.

The Therapeutic Guidelines state that the clinical significance of each parasite is “controversial” and most patients “do not benefit from treatment with antibiotics – consider referral to gastroenterologist”.

However, the guidelines say if other causes have been ruled out then antibiotics can be considered for symptomatic patients.

Writing in the MJA last year, the group claimed the role of these two parasites as GI pathogens was “controversial and unproven” and detection had led to unnecessary treatment with antibiotics, particularly in children.

Since the push began, the Royal College of Pathologists of Australasia has introduced guidelines on PCR testing, recommending doctors exclude the two parasites when testing for faecal pathogens.

One of doctors behind the campaign is Dr Harsha Sheorey, consultant microbiologist at St Vincent’s Hospital in Melbourne.

Dr Sheorey said paediatricians had reported an increase in GP referrals to investigate the presence of Blastocystis species and D fragilis in children with and without IBS symptoms.

“A lot of GPs are sort of forced by the parents, who are… reading up on the net then saying they (or their child) may have this parasite and they want it investigated. In some instances, whole families have been investigated for ‘spread’ of the organisms,” he said.

Most patients requesting the PCR don’t have diarrhoea, he claimed, but rather have “vague symptoms that could be caused by food intolerance or IBS which need to be addressed by a gastroenterologist or by changing their diet”.

“My advice is ‘do not treat, these organisms are not the cause of the problem.”

The push appears to be gaining traction.

Dr Sheorey said the TGA agreed to change its guidelines to advise against treating the two parasites with antibiotics, especially in asymptomatic patients.

Meanwhile, the Australasian Society of Infectious Diseases has also recommended against investigation or treatment for faecal pathogens in the absence of diarrhoea or other gastrointestinal symptoms, listing this as one of the top five low value interventions in the RACP’s EVOLVE initiative.

Dr Asha Bowen, acting chair of Australian and New Zealand Paediatric Infectious Diseases Group (ANZPID), said the society wanted far fewer PCR tests ordered on formed stool, especially in children.

“If the test is ordered and a positive result for D. fragilis or Blastocystis species returned, we recommend that antibiotics are not prescribed as the result is of unclear significance.”

But not all clinicians agree with this message. Sydney GP Professor Kerryn Phelps said she has treated hundreds of patients who tested positive to one or both these parasites, whose symptoms included various combinations of diarrhoea, alternating diarrhoea and constipation, change of bowel habit, cramping, bloating, nausea, recent onset anxiety and weight loss.

She claimed the majority of these patients’ symptoms resolved after treatment.

Professor Phelps, a former AMA president, uses compounded paromomycin (on average for one week) combined with the probiotic Saccharomyces boulardii, followed by a multi-strain probiotic taken for one month combined with a temporary gluten and lactose-free diet until gut symptoms abate, in patients who were immunocompetent.

She points to paromomycin’s eradication rate for D fragilis of 98%, compared to clioquinol (83%) or metronidazole (57%), cited in a paper published in 2012 in the International Journal for Parasitology: Drugs and Drug Resistance.

She also points to the work by gastroenterologist Professor Thomas Borody –who pioneered faecal microbiota transplantation – at his Centre for Digestive Diseases in Sydney, which has developed novel combination antibiotic therapies targeting the two parasites in patients with IBS-like symptoms like diarrhoea, bloating, and nausea.

Professor Phelps said she disagreed with the advice not to test and treat patients with IBS-like symptoms, and was concerned by reports of specialists telling patients to ignore their child’s positive D Fragilis result ‘because it’s not a pathogen’.

“I have seen children who were completely well develop malaise, pallor and abdominal cramping and diarrhoea to the point of soiling themselves and (were) just told (by a gastroenterologist) to go on a low FODMAP diet and anti-depressants.

“I think its contrary to our medical ethics to have a sick patient, clinical experience that a treatment might work for them and deny that to a patient.”

But Professor Phelps believes it’s only a matter of time before the burden of evidence is for pathogenesis is undeniable.

“I think the ground is shifting in people who are researching this intensively,” she said.

“I have been around since people were saying there’s no such thing as a systemic influence of the gut microbiome, or non-celiac gluten sensitivity – these philosophical battles are fought all the time.

“This is exactly what happened to Barry Marshall (in his fight to prove helicobacter pylori caused gastric ulceration).

“Many gastroenterologists are telling people to put up with their symptoms.

“If they truly believe hand on heart, that these are not pathogens they should do a Barry Marshall…swallow a beaker of D fragilis and see what happens.”