Diarrhea

Acute Diarrhea

Most cases of acute diarrhea (< 2 weeks) are due to infections and are self-limited & no additional treatment needed
Infectious:
Watery diarrhea: #1 cause = viral gastroenteritis (norovirus, rotavirus, enteric adenovirus), C. diff, C. perfringens, S. Aureus, Bacillus cereus, enterotoxigenic E. coli, Cryptosporidium, Listeria, Cyclospora, vibrio cholerae, (Giardia is typically more chronic), Tropheryma whipplei, COVID
Inflammatory (bloody) diarrhea: Salmonella, Campylobacter, Shigella, EHEC, Yersinia, E histolytica, invasive viruses (CMV, HSV), Non-cholera vibrio.
Noninfectious: medications (antibiotics, laxatives), ischemia, IBD, radiation, or food intolerance

Obtaining a good clinical history regarding type (watery vs. bloody),risk factors, and associated symptoms (fevers, cramping, severe abdominal pain, tenesmus) is key.
Ask about recent antibiotic exposures or hospitalizations.
- Any antibiotic can cause C. diff; the longer the treatment, the more likely.
- Most common to cause C. diff: Clindamycin > Cephalosporins/Fluoroquinolones/Carbapenems.
Important History: sick contacts, food exposures, travel, occupation (ex: daycares, healthcare), and vulnerable (elderly, immunocompromised, IBD, pregnant).

All patients: CBC w/ diff and BMP to eval for leukocytosis (C.diff), AKI, electrolyte abnormalities, thrombocytopenia/anemia (HUS), eosinophilia (parasites).
If bloody diarrhea, severe illness, immunocompromised, or > 7 days: Cdiff, GIPP, and ESR/CRP.
If immunocompromised: would consider CMV, MAC, microsporidia in addition to above.
If concern for IBD or hx of IBD: CT Enterography with PO and IV contrast and Fecal Calprotectin.

All patients: supportive care with PO or IVF, electrolyte repletion.
Watery Diarrhea:
- Mild illness (no change in daily activities): symptomatic management and treatment with antidiarrheals (start with Loperamide 4mg x1 then transition to 2mg QID (AC+HS) (maximum 16mg/day).
- Moderate-Severe illness:
  - Travel associated: can treat empirically with antibiotics for Traveler’s Diarrhea and adjunctive loperamide + bismuth subsalicylates.
  - Non-travel associated: microbiologic assessment THEN diagnostic directed antimicrobial agent (except STEC infections).
Bloody Diarrhea:
- No fever: microbiologic assessment THEN diagnostic directed anti-microbial agent (except STEC infections).
- Fever + Severe illness:
  - Travel related: treat empirically (Azithro 1000mg x 1 dose OR 500mg daily x 3 days or ciprofloxacin 500mg BID – depending on local susceptibility patterns/travel history) GASTROENTEROLOGY 127.
  - Non-travel related: microbiologic assessment THEN diagnostic directed anti-microbial agent (except STEC infections).
  - Antibiotics for diarrhea are contraindicated in STEC (ex: E.coli O157:H7) as it increases risk for developing HUS.

Secretory	Microscopic colitis (lymphocytic, collagenous), bile acid malabsorption (idiopathic, ileal disease, post-CCY), hormone secreting tumors (VIPoma, gastrinoma, carcinoid), neoplasia (CRC, lymphomas), stimulant laxative abuse
Osmotic	Carbohydrate malabsorption (lactose intolerance, fructose intolerance, sugar alcohol (sorbitol, mannitol, xylitol) ingestion, osmotic laxatives, magnesium-containing supplements
Functional	IBS-Diarrhea predominant, functional diarrhea
Medication-related	Metformin, SSRIs, PPIs, NSAIDs, Colchicine
Post-surgical or Anatomic	Short-bowel syndrome, gastric bypass, SIBO

Small Bowel Malabsorption	Celiac disease, tropical sprue, Whipple disease, giardia
Pancreatic exocrine insufficiency	Chronic pancreatitis, cystic fibrosis, pancreatic cancer
Bile acid deficiency	Ileal Crohn’s Disease, ileal resection, PBC/PSC
Mucosal / Infiltrative disease	Amyloidosis, intestinal lymphoma, radiation enteritis
SIBO-related	SIBO causing deconjugation of bile acids

IBD	Ulcerative Colitis, Crohn’s Disease
Chronic infections	C.diff, CMV, HSV, Entamoeba histolytica, intestinal TB
Ischemia	Chronic mesenteric ischemia, recurrent ischemic colitis
Cancer-related	Colorectal cancer, lymphoma, radiation colitis, ICI colitis

Initial Laboratory for chronic diarrhea: CBC w/diff and iron studies to assess for IDA, CMP, TSH, celiac serologies, fecal calprotectin/CRP if high suspicion.
Alarm features generally trigger endoscopic evaluation. Alarm features include age of onset > 50, rectal bleeding, melena, nocturnal diarrhea, unexplained weight loss, progressive abdominal pain, IDA, abnormal fecal calprotectin.