What is the likely causative agent of acute diarrhea with blood and mucus in a patient?

Acute Diarrhea with Blood and Mucus: Causative Agent

Neither rotavirus nor norovirus is responsible for acute diarrhea with blood and mucus—this presentation indicates invasive bacterial pathogens, most commonly Shigella, Salmonella, Campylobacter, or enteroinvasive E. coli. 1

Why Not Rotavirus or Norovirus?

Viral pathogens cause watery, non-bloody diarrhea. The presence of visible blood and mucus in stool specifically indicates invasive bacterial colitis or amoebic dysentery, not viral gastroenteritis. 1

• Rotavirus is the most common cause of acute diarrhea in children but produces watery diarrhea without blood or mucus 1, 2
• Norovirus causes vomiting and nonbloody diarrhea lasting 2-3 days, with low-grade fever in only 40% of cases 1, 2
• While one case report documented norovirus triggering ischemic colitis with bloody diarrhea, this represents an extremely rare complication rather than typical presentation 3

Actual Causative Agents for Bloody Mucoid Diarrhea

The combination of fever with bloody and mucoid stools is suggestive of invasive bacterial disease or amoebic dysentery. 1

Bacterial Pathogens (Most Likely):

• Shigella, Salmonella, Campylobacter, and enteroinvasive E. coli are the primary bacterial causes of visible blood in stool 1
• Shiga toxin-producing E. coli (STEC) causes severe abdominal pain with grossly bloody stools, though patients are usually not febrile at presentation 1
• Yersinia enterocolitica causes persistent abdominal pain and fever, particularly in school-aged children mimicking appendicitis 1
• Noncholera Vibrio species can cause bloody diarrhea, especially with seafood exposure 1

Parasitic Pathogens:

• Entamoeba histolytica (amoebic colitis) causes bloody diarrhea with a more indolent onset 1
• A wet preparation of recently passed stool (within 15-30 minutes) looking for amoebic trophozoites aids diagnosis 1

Clinical Management Algorithm

Empiric antibiotic treatment should be considered for the combination of fever and significant bloody diarrhea. 1

Antibiotic Selection:

• Cephalosporins or fluoroquinolones are effective for most cases of bacterial dysentery 1
• Macrolides should be used for Campylobacter from Asia due to increasing quinolone resistance 1
• Tinidazole or metronidazole are effective for amoebic dysentery 1

Diagnostic Testing Indications:

• Stool culture for bacterial pathogens is warranted when fever and bloody or mucoid stools are present 1
• Test specifically for STEC O157 when right-sided abdominal pain occurs with bloody diarrhea 1
• Consider amoebic serology and stool examination for trophozoites if travel to endemic areas 1

Critical Pitfall

Do not attribute bloody mucoid diarrhea to viral gastroenteritis. The presence of blood and mucus mandates evaluation for invasive bacterial or parasitic pathogens, as viral etiologies do not cause this presentation except in extraordinarily rare circumstances. 1, 3