New diarrhea guidelines stress implications of molecular tests

New guidelines for diagnosing and managing infectious diarrhea stress that improved tests are capable of detecting multiple organisms in the same patient, which may create a need for infectious disease expertise in interpreting and acting on the findings, the Infectious Diseases Society of America (IDSA) said in releasing the lengthy guidelines today.

The guidelines, which replace IDSA guidance released in 2001, say that most patients who have diarrhea don't need to be tested. But testing is recommended for vulnerable groups: children under age 5, the elderly, immunocompromised patients, and those with bloody diarrhea, severe abdominal pain or tenderness or signs of sepsis. The document was published today in Clinical Infectious Diseases (CID).

"Diagnostic testing combined with clinical expertise is helpful in identifying a cluster of infections that may signal an outbreak," Andi L. Shane, MD, MPH, MSc, lead author of the guidelines, said in an IDSA press release. Shane, an associate professor of pediatric infectious diseases at Emory University School of Medicine and Children's Healthcare of Atlanta, added that even if they don't need to be tested, most patients will benefit from rehydration therapy while waiting for the infection to subside.

Culture-independent tests

Molecular tests that don't rely on culturing of clinical specimens—"culture-independent diagnostic tests" (CIDTs)—are more sensitive than traditional culture-based tests, the IDSA said in the release. "However, they may detect organisms with which most physicians are unfamiliar, or detect more than one microbe. In those cases, consultation with an infectious diseases physician may be beneficial."

In an accompanying commentary, two CID editors said several molecular tests approved by the Food and Drug Administration in recent years can "rapidly detect a broad range of bacterial, viral, and parasitic causes of diarrhea from a single fecal specimen and frequently identify pathogens unsuspected by clinicians."

With the newer tests, clinicians are more likely to reach a specific diagnosis, which may direct appropriate treatment and facilitate public health surveillance efforts, noted the two commentators, Ferric C. Fang, MD, and Robin Patel, MD. Fang works in the departments of laboratory medicine and microbiology at the University of Washington in Seattle, and Patel is with the department of laboratory medicine and pathology at the Mayo Clinic in Rochester, Minn.

But because the reagents used in the tests are expensive, "it is important to limit diagnostic testing for infectious diarrhea to settings in which the tests are likely to yield the most clinically useful results," the commentators said.

Tables aim to help clinicians

The guidelines include seven tables that clinicians can consult for information about how people acquire infections, exposure conditions, postinfectious symptoms, and clinical presentation, as well as recommended antimicrobial, fluid, and nutritional management, the IDSA noted. The tables also should help clinicians assess the need for testing.

"Physicians should ensure that children with mild to moderate dehydration, and children and adults with acute diarrhea and those with mild to moderate dehydration associated with vomiting or severe diarrhea be given oral rehydration solution if tolerated, progressing to intravenous rehydration if oral rehydration is not tolerated," the press release states.

The new guidelines, like the 2001 edition, emphasize that even with the use of CIDTs, it's still essential to obtain bacterial isolates for serotyping studies used in disease outbreak investigations, Fang and Patel wrote. Also, for some microbes, isolates are needed for antimicrobial susceptibility testing.

"For these reasons, directed or 'reflexive' cultures should be performed for pathogens such as Salmonella, Shigella, and Campylobacter species and Escherichia coli O157;H7 when these bacteria are detected by CIDTs," the commentators said. They added that the greater sensitivity of CIDTs is expected to "greatly enhance public health efforts."

The guidelines also strongly recommend that antimicrobial treatment should be modified or stopped when a "clinically plausible organism is identified," Fang and Patel noted. They observed that a number of diarrhea-causing pathogens respond to antimicrobial treatment—and also that antibiotics are contraindicated for Shiga toxin–producing E coli, because they may trigger or exacerbate hemolytic uremic syndrome.

The IDSA noted that the new guidelines mention travel-related diarrhea and Clostridium difficile diarrhea but refer readers to separate guidelines for information on those conditions.

See also:

Full text of new IDSA guidelines in CID

Oct 19 IDSA press release

CID commentary introduction

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