Infectious Diarrhea Guidelines Recommend When to Test

New culture-independent tests are much more sensitive than traditional diagnostic methods in detecting the cause of infectious diarrhea, a significant problem that leads to nearly 500,000 hospitalizations and more than 5,000 deaths in the USA every year.

Diarrhea is defined as three or more loose or liquid stools in 24 hours, or more frequently than is normal for the person. Diarrhea is often, but not always, infectious, meaning that it is thought to be caused by a microbe such as a virus, bacterium or parasite that can spread from person to person.These new tests are so sensitive and may detect multiple organisms, infectious disease expertise may be necessary to interpret the clinical significance and facilitate appropriate public health surveillance.

A panel of experts, led by those at Emory University School of Medicine (Atlanta, GA, USA) have written guidelines that include seven tables that busy clinicians can quickly reference for information about the various ways people acquire the microbes, exposure conditions, post-infectious symptoms and clinical presentation, as well as recommended antimicrobial, fluid and nutritional management. The new infectious diarrhea guidelines provide an update of the 2001 guidelines. While the guidelines mention travel-associated diarrhea and Clostridium difficile diarrhea, other more-specific guidelines on those topics provide detailed guidance and are referenced.

Some of the recommendations for diagnostics include stool testing should be performed for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and Shiga toxin-producing Escherichia coli (STEC) in people with diarrhea accompanied by fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis. Bloody stools are not an expected manifestation of infection with C. difficile. A broader set of bacterial, viral, and parasitic agents should be considered regardless of the presence of fever, bloody or mucoid stools, or other markers of more severe illness in the context of a possible outbreak of diarrheal illness (e.g., multiple people with diarrhea who shared a common meal or a sudden rise in observed diarrheal cases).

All specimens that test positive for bacterial pathogens by culture-independent diagnostic testing such as antigen-based molecular assays (gastrointestinal tract panels), and for which isolate submission is requested or required under public health reporting rules, should be cultured in the clinical laboratory or at a public health laboratory to ensure that outbreaks of similar organisms are detected and investigated. The optimal specimen for laboratory diagnosis of infectious diarrhea is a diarrheal stool sample (i.e. a sample that takes the shape of the container). For detection of bacterial infections, if a timely diarrheal stool sample cannot be collected, a rectal swab may be used. Molecular techniques generally are more sensitive and less dependent than culture on the quality of specimen.

Frequent monitoring of hemoglobin and platelet counts, electrolytes, and blood urea nitrogen and creatinine is recommended to detect hematologic and renal function abnormalities that are early manifestations of hemolytic-uremic syndrome (HUS) and precede renal injury for people with diagnosed E. coli O157 or another STEC infection (especially STEC that produce Shiga toxin 2 or are associated with bloody diarrhea).

Andi L. Shane, MD, MPH, MSc, an associate professor and lead author of the guidelines, said, “Diagnostic testing combined with clinical expertise is helpful in identifying a cluster of infections that may signal an outbreak. However, even if they don't need to be tested, most people will benefit from rehydration therapy while waiting for the infection to run its course.” The study was published on October 19, 2017, in the journal Clinical Infectious Diseases.

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Emory University School of Medicine