In a 31‑year‑old woman with no personal or family history of gastrointestinal disease, who developed acute watery diarrhea one week after eating food outside that progressed to bloody stools, accompanied by fever, abdominal cramping, loss of appetite, stopped loperamide, is using oral rehydration solution, and whose last menstrual period was four days ago, what is the most likely diagnosis and recommended immediate management?

Acute Bacterial Dysentery (Likely Shigella or Campylobacter)

This 31-year-old woman has acute bacterial dysentery requiring immediate stool testing for Shigella, Campylobacter, Salmonella, Yersinia, and STEC, with empiric antibiotic therapy (fluoroquinolone or azithromycin) initiated promptly given the presence of bloody stools, fever, and cramping abdominal pain following food exposure. 1, 2

Diagnostic Approach

Immediate Stool Testing Required

• Stool culture or molecular testing must be obtained for Salmonella, Shigella, Campylobacter, Yersinia, and STEC given the presence of bloody stools, fever, severe cramping, and recent food exposure outside the home 1, 2
• The combination of bloody diarrhea with fever and abdominal cramping strongly suggests invasive bacterial disease requiring pathogen identification 1
• Blood cultures are not routinely indicated in this immunocompetent adult without signs of sepsis or systemic toxicity 1

Key Clinical Features Supporting Bacterial Dysentery

• Bloody stools with mucus (classic for invasive bacterial pathogens) 1
• Subjective fevers (reported in up to 30% of bacterial diarrhea cases) 1
• Cramping abdominal pain during and after bowel movements 1, 2
• Food exposure one week prior (typical incubation period for bacterial pathogens) 1, 3
• Progressive symptoms from watery to bloody diarrhea over 2 days 1

Immediate Management

Fluid Resuscitation

• Continue oral rehydration solution aggressively as the patient can tolerate oral intake and shows no signs of severe dehydration 2, 3
• Monitor for signs requiring IV hydration: inability to tolerate oral fluids, altered mental status, hemodynamic instability, or signs of sepsis 2

Empiric Antibiotic Therapy

Empiric antibiotics should be initiated immediately without waiting for stool culture results given the combination of fever and bloody diarrhea, which is highly suggestive of invasive bacterial disease 1

First-Line Options:

• Ciprofloxacin 500 mg twice daily for 3-5 days (fluoroquinolones are first-line for empiric treatment of bacterial dysentery) 1
• Alternative: Azithromycin 500 mg once daily for 3 days if Campylobacter is suspected (increasingly quinolone-resistant, especially from Asia) or if the patient is pregnant 1

Critical Caveat:

• Do NOT use antibiotics if STEC (E. coli O157:H7 or other Shiga toxin-producing E. coli) is strongly suspected, as this increases the risk of hemolytic uremic syndrome (HUS) 1, 2
• STEC typically presents with severe cramping and bloody diarrhea but often WITHOUT fever, which makes it less likely in this febrile patient 1

Antidiarrheal Agents

• Loperamide should remain discontinued as it was appropriately stopped when blood appeared in the stool 1
• Antimotility agents are contraindicated in bloody diarrhea and febrile illness due to risk of prolonging infection, toxic megacolon, and worsening clinical course 1, 4

Monitoring and Follow-Up

Clinical Reassessment

• Monitor for worsening symptoms: increasing fever, worsening abdominal pain, signs of peritonitis, or hemodynamic instability requiring hospitalization 2
• Reassess hydration status every 4-6 hours during acute phase 2
• Watch for complications: severe dehydration, sepsis, or development of HUS (especially if STEC is identified) 1, 2

Dietary Management

• Resume normal diet as tolerated once nausea and vomiting resolve; early refeeding is preferred over prolonged fasting 1, 2
• Avoid large meals initially to minimize gastrocolic reflex in a hyperactive gut 1

When to Hospitalize

Hospitalization criteria include: 2

• Severe dehydration despite oral rehydration attempts
• Inability to tolerate oral intake
• Signs of sepsis (hypotension, tachycardia, altered mental status)
• Severe or worsening abdominal pain suggesting peritonitis or toxic megacolon
• Immunocompromised state

Special Considerations

Pregnancy Status

• The patient is sexually active without contraception and her LMP was 4 days ago, making early pregnancy unlikely but not impossible 2
• If pregnancy is confirmed, avoid fluoroquinolones and use azithromycin instead 1

Public Health Reporting

• Positive cultures for Shigella, Salmonella, Campylobacter, Yersinia, or STEC require public health notification to facilitate outbreak detection and contact tracing 1

Common Pitfalls to Avoid

• Do not delay empiric antibiotics while waiting for stool culture results in a patient with bloody diarrhea and fever 1
• Do not use antimotility agents (loperamide, diphenoxylate) in bloody or febrile diarrhea 1, 4
• Do not assume viral gastroenteritis when blood is present in stool—this mandates bacterial workup 1, 3
• Do not give antibiotics empirically if STEC is the leading diagnosis (though less likely here given fever) 1, 2