- RECENT ANTIBIOTIC USE—consider Clostridium Difficile.
- RECENT CAMPING (or drinking water form a lake, pond, or stream)—consider Guardia. I once had a man who maintained fountains in ponds who we diagnosed with Guardia. My only case in the last 10 years.
- CHRONIC WEIGHT LOSS—consider looking for colon cancer or inflammatory bowel
- ABDOMINAL PAIN or BLOODY STOOLS—Consider invasive organism such as salmonella. Also entertain other infectious causes of abdominal pain.
Again, those are just some of the "red flags" off the top of my head. Do you have any others?