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Causes of Persistent Diarrhea Identifiable Through New Testing Methods

HOUSTON – Emergency department clinicians need to be alert when diagnosing persistent vs. acute diarrhea in patients, according to a new journal article suggesting that many physicians fail to focus on how long patients have had the condition.

Persistent diarrhea, which lasts at least 14 days, is an illness typically caused by parasites or bacteria and requires accurate diagnosis to determine what treatment to provide, according to a literature review published recently in the Journal of the American Medical Association.

In the review, Herbert L. DuPont, MD, director of the Center for Infectious Diseases at The University of Texas Health Science Center at Houston School of Public Health, warns that persistent diarrhea from some causes can result in serious nutritional disorders and malnutrition.

"I'd like to educate doctors about the importance of taking the history and assessing duration of illness,” DuPont writes. “For acute diarrhea, the lab has a minimal role, restricted to patients passing bloody stools. If a patient has had diarrhea for two weeks or more, the doctor should focus on the cause of the disease through laboratory testing, with an emphasis on parasites.”

According to the review, acute diarrhea lasts less than two weeks and typically is caused by viruses or toxins.

Persistent diarrhea, on the other hand, is caused most commonly by bacteria or parasites, including Giardia, Cryptosporidium, and Cyclospora or, less commonly, Entamoeba histolytica, Dientamoeba fragilis, Strongyloides stercoralis, and Microsporidia species.

The parasites can be contracted through food, water, or from other people and are commonly picked up while traveling. They also can be detected in laboratory testing, DuPont points out.

During the past year, he notes, a new testing method — multiplex polymerase chain reaction (PCR) — was developed, and the simultaneous, single test identifies unique DNA sequences to detect a panel of causes of diarrhea.

Two platforms have been approved by the Food and Drug Administration for use, according to the article. In the past, researchers had to culture bacteria from a stool sample and examine it for isolated bacteria, or look under a microscope for parasites. In addition, commercial enzyme immunoassay could be used to identify three of the parasites. Yet, those methods were limited in their ability to pinpoint causation.

"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,” DuPont explains. “The technology needs to be more widely available. Diagnosis is critical when treating persistent diarrhea.”

In terms of treatment, he emphasizes, a lab-established diagnosis is necessary before instituting antimicrobial therapy. Nitazoxanide is a drug that treats a broad spectrum of parasites and can be used as treatment for patients with persistent diarrhea who test negative for a pathogen in the lab, DuPont adds.

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