Laboratory diagnosis of Clostridioides difficile infection: past, present and future.

Clostridioides difficile is a gram-positive, spore-forming anaerobic enteropathogen responsible for a wide spectrum of clinical diseases ranging from mild diarrhoea to pseudomembranous colitis or toxic megacolon. It is the main cause of healthcare-associated diarrhoea, but community-associated Clostridioides difficile infections (CDI) have been increasingly reported in the past few years. This narrative review aims to provide a comprehensive overview of the methods and most recommended strategy, and a brief description of the main pitfalls and new developments in CDI diagnosis. Underdiagnosis still remains important due to a lack of physicians' awareness for CDI. Appropriate selection of stool samples, and implementation of rejection criteria at the lab level are essential to provide an accurate diagnosis of CDI. Methods used for the diagnosis are usually classified into 3 groups according to their targets: those detecting the presence of C. difficile (culture, enzyme immunoassays [EIA] for glutamate dehydrogenase [GDH]), those detecting free toxins in stools (EIA for toxins) and those detecting a toxigenic C. difficile strain (nucleic acid amplification test [NAAT], toxigenic culture). No stand-alone method can be used for the CDI diagnosis. The European Society for Clinical Microbiology and Infectious Diseases (ESCMID) recommends a two-step algorithm with a sensitive screening test (NAAT or GDH EIA). If the screening test is negative, the CDI diagnosis can be ruled out. If the screening test is positive, a second highly specific test targeting free toxins should be used, such as EIA for toxin A/B. Implementing this strategy enables a better accuracy of CDI diagnosis, thus improving patient's management and clinical outcomes.