Acute watery diarrhoea and food poisoning: identifying the organism

The first split: blood or no blood

Diarrhea is split first by bloody vs no blood, and by WBC in stool.

• Bloody: salmonella, Shigella, Yersinia, E.coli 0157, campylobacter.
• No blood: S. aureus, b.cereus, Giardia, cryptosporidium, viral.

Two lines about what is most common sit side by side and are worth keeping apart: the most common agent causing food poisoning is Campylobacter, while Norovirus is the most common cause at the head of the watery diarrhea table.

Three food links are given: contaminated poultry and eggs is Salmonella; E. coli 0157:H7 is associated with undercooked hamburger meat; and E. coli 0157:H7 and Shigella are associated with hemolytic uremic syndrome (HUS).

Reading the agent off the clock and the plate

• Norovirus, the most common cause. Onset very short, even < 1 hour. Watery diarrhea and vomiting are the primary features, with fever, headache and myalgia. Clue in history: outbreaks in hospitals, nursing homes. Treatment supportive.
• Staphylococcus aureus. Onset within 24 hrs (1-6 hrs) after exposure. No fever, N/V, with or without diarrhea. Clue: food poisoning, meat. Treatment supportive.
• Clostridium perfringens. Onset 8 to 16 hours. Crampy abdominal pain. Clue: meat, poultry, gravy, home-canned goods.
• Bacillus cereus. Very rapid, within hours. Diarrhea and vomiting. Clue: rice-based dishes, and fried rice in particular. Symptoms generally resolve within 1-2 days.
• Giardia lamblia. Onset 7-14 days. Foul-smelling, floating stool that is hard to flush, explosive, with abdominal bloating. Clue: travel, hiking, camping, swimming pools. Giardia lamblia and cryptosporidiosis are acquired from contaminated water sources, fresh water found on a camping trip. Treatment metronidazole.
• Vibrio cholera. Onset within a few hours. Vomiting and muscle cramps; diarrhea severe, with severe dehydration and electrolyte imbalance; rice-water stool. Clue: raw seafood and shellfish, contaminated water. Treatment supportive, which involves replacing lost fluids and electrolytes, with antibiotics as well - doxycycline.
• Clostridium difficile. Onset 1-11 weeks. Prior antibiotic use, clindamycin is common. Treatment oral vancomycin, alternative is metronidazole.