Molecular-based diagnostic tests for enteric pathogens are highly sensitive but may require expert input to assess their clinical and public health implications, according to new guidelines from the Infectious Diseases Society of America.
Among the specific areas on which the guidelines focus are assessment of the diagnostic needs of patients who have been traveling, those in health care settings, including long-term care facilities, and dealing with immunocompromised patients, especially those with acquired immune deficiency syndrome (AIDS).
“Differentiating colonization from active infection, obtaining antimicrobial susceptibility results, providing optimal management, and preventing transmission are areas in need of additional research as nonculture diagnostics replace traditional culture-based methods,” writes Andi L. Shane, MD, of Emory University and Children’s Healthcare in Atlanta, with her associates in Clinical Infectious Diseases. Performing a complete physical exam and taking a thorough exposure history remain crucial in this era of rapid molecular tests in order to identify and treat infectious diarrhea and interrupt the chain of transmission, the experts emphasize (Clin Infect Dis. 2017 Oct 19.).
The rise of culture-independent diagnostic tests also has important public health implications, the experts state. Pulsed-field gel electrophoresis and whole-genome sequencing are essential for rapidly detecting outbreaks, but they must be performed on clinical isolates. “Continuing to detect and respond to such outbreaks is a vital part of making our food and water systems safer,” the authors add. “As culture-independent diagnostic panels become used more frequently, public health departments may request that specimens be cultured in public health laboratories if unable to be cultured in the clinical diagnostic laboratory.” Clinicians should continue submitting isolates for subtyping of notifiable pathogens, such as Salmonella, Shiga toxin–producing Escherichia coli, Shigella, and Listeria, according to the guidelines.
The guidelines also recommend a broad differential diagnosis in immunocompromised people with diarrhea, and people with AIDS who have persistent diarrhea should undergo additional testing for other organisms including, Cryptosporidium, Cyclospora, Cystoisospora, Microsporidia, Mycobacterium avium complex, and Cytomegalovirus.
The IDSA last updated its guidelines on infectious diarrhea in 2001. The current iteration includes 60 specific recommendations and five tables that stratify pathogens by exposures, clinical signs and symptoms, postinfectious sequelae, laboratory diagnostics, and antimicrobial therapy. Two additional tables list other sources of guidelines and provide detailed recommendations on rehydration therapy. Most patients with diarrhea do not need to be tested for infectious pathogens, with exceptions such as children younger than 5 years, the elderly, immunocompromised patients, and patients with bloody diarrhea, severe abdominal pain or tenderness, or signs of sepsis. Even when patients do not need to be tested, they should receive oral rehydration solution to correct mild to moderate dehydration or intravenous rehydration if they cannot tolerate oral therapy.
The World Health Organization defines diarrhea as loose or liquid stools occurring three or more times in 24 hours or more often than normal. Rapid molecular tests most often identify norovirus in these patients. Infectious diarrhea remains most common in children under age 5 years, but the advent of rotavirus vaccines over the past decade has decreased its incidence in this age group.
The work was funded by IDSA. Dr. Shane disclosed research grants from the Division of Microbiology and Infectious Diseases of the National Institute of Allergy and Infectious Diseases, salary support from the Gerber Foundation, honoraria from SLACK, and travel support from International Scientific Association for Probiotics and Prebiotics.
This article was updated 11/3/17.