Differential Diagnosis

The patient presents with symptoms of food poisoning, including diarrhea, abdominal pain, and nausea, which have been improving with treatment. However, the development of new symptoms such as fever, rigors, a sore throat, and abdominal tenderness warrants a thorough differential diagnosis.

• Single most likely diagnosis:
  • Gastroenteritis: The patient's initial symptoms of diarrhea, abdominal pain, and nausea are consistent with gastroenteritis, likely caused by a viral or bacterial infection. The improvement with oral rehydration solution and loperamide also supports this diagnosis.
• Other Likely diagnoses:
  • Viral pharyngitis: The development of a sore throat and slightly erythematous throat examination suggests a viral pharyngitis, which could be a separate infection or related to the initial gastroenteritis.
  • Inflammatory bowel disease (IBD) exacerbation: Although the patient has no prior history of IBD, the abdominal pain, diarrhea, and rebound tenderness could be indicative of an IBD flare. However, this would be less likely given the acute onset and improvement with treatment.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Appendicitis: The abdominal tenderness, guarding, and rebound tenderness, particularly on the left side, could be indicative of appendicitis, which requires prompt surgical intervention.
  • Septicemia: The patient's fever, rigors, and tachycardia could be signs of septicemia, which would require immediate antibiotic treatment and supportive care.
  • Foodborne bacterial infection (e.g., Salmonella, E. coli): Although the patient's symptoms have improved, a foodborne bacterial infection could still be present, and certain strains (e.g., E. coli O157:H7) can cause life-threatening complications like hemolytic uremic syndrome (HUS).
• Rare diagnoses:
  • Intussusception: Although rare in adults, intussusception could cause abdominal pain, diarrhea, and vomiting, and would require prompt surgical intervention.
  • Mesenteric lymphadenitis: This condition, also known as mesenteric adenitis, can cause abdominal pain, diarrhea, and fever, and is often mistaken for appendicitis.