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New infectious diarrhea guidelines developed by the Infectious Diseases Society of America (IDSA) reflect advances in culture-independent diagnostic tests (CIDT) and their applications in diagnosing and managing this condition. Citing some limitations of these tests, the authors recommend following up with culture on any positive CIDT results for pathogens for which public health authorities request or require reporting.

Updating the 2001 IDSA recommendations, the new material advises clinicians to have detailed discussions with patients about their health history, and to assess both symptoms and exposure history to guide diagnosis and management of diarrhea. It’s also important to collaborate with labs and local public health entities, Andi L. Shane, MD, MPH, MSc, lead author of the guidelines and associate professor of pediatric infectious diseases at Emory University School of Medicine and Children’s Healthcare of Atlanta, told CLN Stat.

Laboratories serve as the eyes of a clinical team, Shane continued. “Collaboration among laboratorians, clinicians, and representatives from public health ensure that patients are optimally managed and that clusters of infections with public health significance are identified and contained.”

The guideline refers to various CIDTs, which have been developed rapidly in recent years. “These tests integrate sample preparation, amplification, detection, and analysis resulting in a rapid turn-around time that could impact patient care,” Shane said. The most common of these tests is the GI panel which involves molecular testing for bacterial, viral, and parasitic pathogens in stool, she said.

Nucleic acid amplification tests (NAAT) are a type of CIDT that detect nucleic acids of organisms in a much shorter timespan than traditional assays. Multiplex gastrointestinal panels include the detection of norovirus, enterotoxigenic Escherichia coli (ETEC), enteropathogenic E. coli (EPEC), and enteroaggregative E. coli (EAEC). “The short time to results could reduce inappropriate use of antimicrobial agents to treat infections that do not require antimicrobial therapy and could shorten the time to targeted management and isolation measures for certain infections such as [Shiga toxin–producing E. coli],” (STEC O157) according to the guidelines.

In a succinct table the authors list the laboratory diagnostic tests for the various organisms that cause infectious diarrhea. Multiplex testing detects Clostridium difficile, Salmonella enterica, Shigella spp, Campylobacter spp, STEC O157, and a variety of other pathogens. Another type of CIDT, enzyme immunoassays or EIAs, detect rotavirus or enteric adenovirus. The guidelines recommend both EIA and NAAT tests for G. lamblia and these tests plus direct fluorescent immunoassay for Cryptosporidium spp.

The authors also offer some perspective on CIDT use. In particular, the clinical relevance of detecting multiple organisms in a specimen is sometimes unclear because it’s not always known which organism is responsible for a patient’s illness.

“Replacement of culture by CIDT in clinical laboratories will impact outbreak detection and investigation…Replacement of culture by CIDT without preserving access to isolates will impede detection of dispersed outbreaks, and thus reduce the capacity of public health to control and to prevent them,” the guideline authors emphasized.

Because new multiplex NAAT tests detect DNA instead of viable pathogens, the guidelines recommend that clinicians take certain considerations when interpreting the results of these tests.

In the event a sample tests positive by CIDT and isolate submission is called for by public health reporting rules, the short-term recommendation is to culture the specimen at a clinical or public health lab. “Cultured organisms can be sent to public health laboratories for species identification, serotyping and further subtyping by molecular methods (e.g., pulsed-field gel electrophoresis, and, more recently, whole-genome sequencing),” they suggested. “In the longer term, culture-independent methods that serve clinical diagnostic needs and are able to identify organism subtypes and their susceptibility patterns are needed.