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Polymerase chain reaction testing for faecal parasites: risks and alternatives

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In this short report, written on behalf of the Australian Society of Infectious Diseases (ASID) and endorsed by its council, we highlight recent changes to stool pathogen testing (particularly for parasites) within Australasian laboratories and alert clinicians to our concerns regarding result interpretation.

Since 2013, many laboratories in Australasia have changed the technique used for stool parasite detection from subjective, time-consuming microscopy to multiplex polymerase chain reaction (PCR), which can detect multiple enteric bacterial and parasitic pathogens. A turnaround time of under 3 hours increases efficiency and reduces costs.1 Five protozoa are generally included in multiplex PCR assay: Giardia lamblia, Cryptosporidium spp., Entamoeba histolytica, Dientamoeba fragilis and Blastocystis spp.1

ASID and the Royal College of Pathologists of Australasia (RCPA) have significant concerns regarding two parasites included in multiplex PCR assay — D. fragilis and Blastocystis spp. — as their role as putative gastrointestinal pathogens is controversial and unproven. Both D. fragilis and Blastocystis spp., which are of uncertain clinical significance and may be colonising flora, have been detected at much higher rates by PCR than by routine microscopy, with prevalence rates…