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Cross-Cutting· Chapter 33

GI Infections

Clostridioides difficile diagnosis and severity grading, fidaxomicin versus vancomycin selection, FMT and bezlotoxumab for recurrent disease, travelers' diarrhea, the major parasites, Strongyloides screening before immunosuppression, CMV colitis versus MAC versus IRIS in the immunocompromised host, and the norovirus and Cryptosporidium framework.

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What this chapter covers

  • Section 33.1: Clostridioides difficile diagnosis and severity

    Clostridioides difficile infection (CDI) causes approximately 500,000 infections and 30,000 deaths annually in the United States, with hospital-onset and community-onset cases roughly equal.

  • Section 33.2: Clostridioides difficile first-episode and fulminant treatment

    The first-line agent for CDI shifted from vancomycin to fidaxomicin in the 2021 ACG and IDSA-SHEA updates, based on the OPT-80-003 trial result that fidaxomicin and vancomycin produced similar clinical cure rates (approximately 88 percent versus 86 percent) but fidaxomicin reduced sustained recurrence by approximately 14 percentage points.

  • Section 33.3: Recurrent C. diff, bezlotoxumab, FMT, and live biotherapeutics

    A first recurrence of CDI affects 20 to 30 percent of treated patients, and the risk climbs above 60 percent after a third episode.

  • Section 33.4: Travelers' diarrhea and bacterial enterocolitis

    Travelers' diarrhea affects 30 to 50 percent of travelers from high-income to low- and middle-income regions.

  • Section 33.5: Parasitic GI infections

    Parasitic GI infection is suspected by exposure (untreated water, daycare, recent travel, immunocompromise), persistence beyond 7 to 14 days, or specific clinical patterns (steatorrhea with weight loss for Giardia, dysentery with hepatic abscess for Entamoeba histolytica, hyperinfection during steroid initiation for Strongyloides, peripheral eosinophilia for Strongyloides or Cystoisospora).

  • Section 33.6: CMV colitis

    Cytomegalovirus (CMV) is a human herpesvirus that establishes lifelong latent infection after primary exposure and reactivates under immunosuppression.

  • Section 33.7: MAC, microsporidia, and Cyclospora

    Mycobacterium avium complex, microsporidia, and Cyclospora are the opportunistic enteric pathogens whose pathogen-level diagnostic and treatment detail Ch 33 owns; the broader CD4 stratification framework, immune reconstitution inflammatory syndrome, and Kaposi sarcoma as a tissue diagnosis live in Ch 34.

  • Section 33.8: Norovirus and viral gastroenteritis

    Norovirus is the leading cause of acute community-acquired and outbreak gastroenteritis in the United States and globally, year-round with a cold-weather peak.

Podcast episodes

  1. 01

    C Diff Diagnosis and Treatment

    This episode covers Clostridioides difficile from diagnosis through the first episode and fulminant disease: the two-step diagnostic algorithm of NAAT plus toxin EIA, severity stratification that guides treatment, fidaxomicin as first-line with oral vancomycin as the established alternative, and fulminant C.

  2. 02

    C Diff Recurrence

    This episode covers the recurrence toolkit for Clostridioides difficile: extended-pulse fidaxomicin and tapered-pulsed vancomycin, the host- immunity layer of bezlotoxumab, the live biotherapeutic products that replaced uncontrolled fecal transplant, and oral vancomycin prophylaxis.

  3. 03

    Travelers Bacterial Toxins

    This episode covers the community-acquired bacterial diarrheas: travelers' diarrhea chosen by region with empiric azithromycin or rifaximin, the bacterial enterocolitis pathogens including the no- antibiotics-for-EHEC rule because of hemolytic-uremic syndrome risk, and the foodborne toxin syndromes recognized by the time to onset.

  4. 04

    Parasitic and Viral

    This episode covers the parasitic and viral diarrheal infections: the parasites from Giardia to Entamoeba histolytica to Strongyloides hyperinfection in steroids, and the viral gastroenteritis differential led by norovirus.

  5. 05

    Immunocompromised Infections

    This episode covers the enteric infections that target the immunocompromised host: CMV colitis with owl-eye intranuclear inclusions on biopsy of the ulcer base and ganciclovir as primary therapy, MAC enterocolitis with macrolide-containing regimens, microsporidia, and Cyclospora with trimethoprim-sulfamethoxazole as treatment of choice.