STEPTRACKERMICROBIOLOGY + GASTROENTEROLOGY | INFECTIONS BY SYSTEM | HIGH-YIELD REVIEW

Diarrhea & Food Poisoning

Three questions sort infectious diarrhea: how soon after the meal, is there blood or fever, and what was eaten or where was the patient.

FOCUS ON
Incubation: 1–6 h → preformed toxin (S aureus — mayonnaise, custards, deli; B cereus — reheated rice) → vomiting; 8–16 h → C perfringens (reheated meat; watery, cramps); 1–3 days → invasive or enterotoxigenic organisms. Bloody (inflammatory): Campylobacter, Salmonella, Shigella, EHEC, EIEC, Yersinia, C difficile, Entamoeba. Watery: ETEC, V cholerae, C perfringens, viruses (norovirus, rotavirus), Giardia, Cryptosporidium. C difficile: recent antibiotics (clindamycin, fluoroquinolones, cephalosporins) → toxins A/B → pseudomembranous colitis → oral vancomycin or fidaxomicin. Treat most with fluids; avoid antibiotics in EHEC.
ORGANISM
FOOD · SETTING
ONSET · STOOL
CLUE
Staphylococcus aureus
Mayonnaise, potato/egg salad, custard, ham left at room temperature
1–6 h · vomiting > diarrhea, no fever
Heat-stable preformed enterotoxin
Bacillus cereus
Fried rice kept warm (emetic) · meats, vegetables (diarrheal)
1–6 h vomiting · or 8–16 h watery
Cereulide (emetic toxin) survives reheating
Clostridium perfringens
Reheated meats, gravies, large batches
8–16 h · watery, cramps, short
Enterotoxin released during sporulation in gut
Norovirus
Cruise ships, nursing homes, shellfish
12–48 h · vomiting + watery
Most common cause overall
ETEC
Contaminated water/food abroad
1–3 days · watery
Most common traveler's diarrhea
Vibrio cholerae
Contaminated water, endemic regions
1–3 days · massive rice-water
Oral rehydration
Campylobacter jejuni
Poultry, raw milk
2–5 days · bloody, fever, pain
Guillain-Barré later
Nontyphoidal Salmonella
Poultry, eggs, reptiles
8–72 h · fever, diarrhea ± blood
Avoid antibiotics unless severe/high risk
Shigella
Person-to-person, daycare
1–3 days · dysentery, tenesmus
Very low dose
EHEC O157:H7
Undercooked ground beef, raw produce, petting zoos
3–4 days · bloody, little fever
HUS · no antibiotics
Yersinia enterocolitica
Pork, chitterlings, milk
4–7 days · bloody, RLQ pain
Pseudoappendicitis
Clostridioides difficile
Antibiotics, hospital, PPIs, age; spores resist alcohol gel
Watery (sometimes bloody) diarrhea, fever, leukocytosis; toxic megacolon
Stool toxin/PCR · oral vancomycin or fidaxomicin · fecal transplant for recurrence · soap and water
Listeria (food-borne)
Deli meats, soft cheese, melons
Febrile gastroenteritis; bacteremia, meningitis in pregnancy, elderly
Grows in the refrigerator
Parasites
Giardia (streams), Cryptosporidium (pools), Entamoeba (travel)
Prolonged (> 7–14 days)
See 9.01

Mechanism — two ways to cause diarrhea

EnterotoxinCholera, ETEC
→
↑ cAMP/cGMP → Cl⁻ secretion
→
Watery, no WBCsSmall bowel
Invasion or cytotoxinShigella, Campylobacter, EHEC
→
Mucosal destruction
→
Blood, fever, fecal WBCsColon

Sort by incubation

ONSET
MECHANISM
ORGANISMS
1–6 h
Preformed toxin
S aureus, B cereus (emetic)
8–16 h
Toxin made in gut
C perfringens, B cereus (diarrheal)
1–3 days
Colonization / invasion
Norovirus, ETEC, Salmonella, Shigella, Campylobacter
> 1 week
Parasites
Giardia, Cryptosporidium, Cyclospora, Entamoeba

How it's tested

COMMON CONFUSIONVomiting a few hours after a picnic (preformed S aureus toxin) vs bloody diarrhea days later (invasive organism) — timing separates them before any test.
THE TRAPAlcohol gel doesn't kill C difficile spores — wash hands with soap and water and use bleach for surfaces.
YOUR APPROACHOnset → blood/fever → food or setting → organism → fluids for most; targeted drugs for C difficile, severe Shigella/Campylobacter, parasites; no antibiotics for EHEC.

If you see… think…

Vomiting 3 hours after potato salad at a picnic → S aureus toxin
Vomiting 2 hours after reheated fried rice → B cereus
Watery diarrhea 12 hours after reheated gravy → C perfringens
Nursing home outbreak of vomiting and diarrhea → norovirus
Bloody diarrhea then Guillain-Barré → Campylobacter
Child with bloody diarrhea after a petting zoo, later AKI → EHEC (HUS)
Diarrhea and leukocytosis after clindamycin → C difficile
Yellow plaques on colonoscopy → pseudomembranous colitis
Pregnant woman with febrile diarrhea after deli meat → Listeria
Diarrhea lasting 3 weeks after camping → Giardia