Laboratory Diagnosis Required for Treating Patients with Persistent Diarrhea

Acute diarrhea lasts less than two weeks and is typically caused by viruses or toxins. Persistent diarrhea is most commonly caused by bacteria or parasites, including Giardia, Cryptosporidium and Cyclospora. Less common parasites are Entamoeba, Cystoisospora belli (Isospora belli), Dientamoeba fragilis, Strongloides stercoralis and microsporidia. These parasites, which can be detected in laboratory testing, can be contracted through food, water or from other people and are commonly picked up while traveling.

Previously, microbiologists would culture bacteria from a stool sample and examine it for isolated bacteria. For parasites, they would either look under a microscope or, for three of the parasites, use commercial enzyme immunoassays. Both methods were only able to identify a small number of parasites. A novel testing method called multiplex polymerase chain reaction (PCR) was developed within the past year. This simultaneous, single test identifies unique DNA sequences to detect a panel of causes of diarrhea. Two multiplex platforms are commercially available: the xTAG Gastrointestinal Pathogen Panel (Luminex Corporation, Austin TX, USA), which tests for 14 viruses, bacteria, and parasites and the FilmArray GI panel (Biofire Diagnostics, Salt Lake City, UT, USA) that tests for 22 viruses, bacteria, and parasites.

Herbert L. DuPont, MD, the author of the review said, “These new tests are easy to use, are capable of detecting a broad range of pathogens and represent a significant improvement over culture-based diagnostic approaches. The technology needs to be more widely available. Diagnosis is critical when treating persistent diarrhea. Antimicrobial therapy can be useful for many patients with persistent diarrhea, but a lab-established diagnosis is necessary for treatment.” The study was published in the June 2016 issue of the Journal of the American Medical Association.

Related Links:
The University of Texas Health Science Center
Luminex
Biofire Diagnostics