Differential Diagnosis for 42-year-old Female with Diarrhea and Abdominal Pain

Single Most Likely Diagnosis

• Recurrence of E. coli colitis or persistent infection: Given the recent history of E. coli colitis treated with Bactrim, it's plausible that the infection was not fully eradicated or has recurred, especially if the treatment course was not completed or if the strain was resistant to Bactrim.
• Relapse of C. difficile infection: Despite multiple fecal transplants, the patient could be experiencing a relapse of C. difficile infection, which is known for its high recurrence rate, especially in patients with compromised gut microbiota.

Other Likely Diagnoses

• Irritable Bowel Syndrome (IBS) exacerbation: The patient's history of IBS could be contributing to the current symptoms, especially if there have been changes in bowel habits, stress, or dietary factors.
• Bactrim-induced diarrhea: Although less common, Bactrim (sulfamethoxazole/trimethoprim) can cause diarrhea as a side effect, which might be contributing to the patient's symptoms.
• Gastrointestinal infection with another pathogen: Other bacterial, viral, or parasitic infections could be causing the diarrhea, considering the patient's history of gastrointestinal issues and recent antibiotic use.

Do Not Miss Diagnoses

• Toxic megacolon: Given the patient's history of toxic megacolon, it's crucial to rule out a recurrence, as this condition can be life-threatening and requires prompt intervention.
• Inflammatory bowel disease (IBD) flare: Although not explicitly mentioned, if the patient has a history of IBD (e.g., Crohn's disease, ulcerative colitis), a flare could be causing the symptoms, and missing this diagnosis could lead to significant morbidity.
• Sepsis or severe infection: Any severe infection, including those not yet identified, could lead to sepsis, a potentially fatal condition if not promptly recognized and treated.

Rare Diagnoses

• Chronic intestinal pseudo-obstruction: This rare condition involves impaired intestinal motility, which could cause the patient's symptoms, especially if there's a history of abdominal surgery or other predisposing factors.
• Gastrointestinal lymphoma or other malignancies: Although rare, gastrointestinal malignancies could cause chronic diarrhea and abdominal pain, and a thorough evaluation might be necessary to rule out these conditions, especially in the context of persistent or recurrent symptoms.

Consultations

Given the complexity of the patient's history and the potential for multiple contributing factors, consultations with Gastroenterology and Infectious Disease specialists would be beneficial to guide further diagnostic workup and management. Depending on the clinical course and findings, Surgery consultation might also be necessary if there's suspicion of a condition requiring surgical intervention, such as toxic megacolon or a complication of IBD.