What is the differential diagnosis and initial evaluation for a patient presenting with fever, abdominal pain, nausea, vomiting, and cough?

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Differential Diagnosis for Fever, Abdominal Pain, Nausea, Vomiting, and Cough

The combination of fever, abdominal pain, nausea, vomiting, and cough requires immediate consideration of both intra-abdominal infection and COVID-19, with CT abdomen/pelvis being the imaging modality of choice after initial stabilization. 1, 2

Primary Differential Diagnoses

Infectious Etiologies

  • Complicated intra-abdominal infection (appendicitis, diverticulitis, abscess, cholangitis, pancreatitis, inflammatory bowel disease complications) - the classic presentation includes rapid-onset abdominal pain with gastrointestinal dysfunction (nausea, vomiting) and signs of inflammation (fever, tachycardia, tachypnea) 1
  • COVID-19 with gastrointestinal manifestations - can present with abdominal pain (2.9-6.8% of cases) through direct viral infection of ACE2-expressing GI cells, referred pain from lower lobe pneumonia affecting the diaphragm, or systemic inflammatory response 2
  • Lower lobe pneumonia with referred abdominal pain - diaphragmatic irritation from pneumonia can mimic acute abdominal conditions 2
  • Gastroenteritis with secondary pneumonia or vice versa 3

Non-Infectious Etiologies

  • Malignant conditions including lymphoma, necrotizing masses, or masses producing secondary infections 1
  • Ischemic bowel disease - particularly in patients with cardiovascular risk factors 1

Initial Evaluation Algorithm

Step 1: Immediate Assessment and Stabilization

  • Perform rapid history and physical examination focusing on: onset/character of pain, localization, peritoneal signs, respiratory symptoms, travel history, immunosuppression status, and hemodynamic stability 1
  • Initiate immediate volume resuscitation - volume depletion is common due to fever, poor intake from nausea/vomiting, and tachypnea-induced evaporative losses 1
  • Begin IV fluid therapy as soon as intra-abdominal infection is suspected, even without volume depletion 1
  • For septic shock: resuscitation and antibiotics must begin immediately when hypotension is identified 1

Step 2: Laboratory Studies

  • Obtain routine labs including complete blood count, comprehensive metabolic panel, liver enzymes (AST, ALT, bilirubin), and lactate 1
  • COVID-19 RT-PCR nasopharyngeal swab - essential during pandemic or when respiratory symptoms present, as GI symptoms may be the only initial manifestation in some patients 2
  • Blood cultures if septic shock present or if results will change management 3

Step 3: Imaging Selection

  • CT abdomen and pelvis with IV contrast is the imaging modality of choice for determining presence and source of intra-abdominal infection in adult patients not undergoing immediate laparotomy 1
  • Chest CT or lung ultrasound should be considered to evaluate for COVID-19 pneumonia or lower lobe pneumonia causing referred abdominal pain 2
  • Plain radiographs have limited utility - low sensitivity for sources of abdominal pain/fever despite high sensitivity for foreign bodies and moderate sensitivity for obstruction 1

Step 4: Antimicrobial Therapy

  • Initiate broad-spectrum antibiotics once intra-abdominal infection is diagnosed or considered likely, ideally in the emergency department 1
  • For septic shock: antibiotics must be administered as soon as possible, as delays are associated with poorer outcomes 1

Critical Pitfalls to Avoid

COVID-19 Considerations

  • Do not dismiss COVID-19 in patients without respiratory symptoms - gastrointestinal symptoms may be the only initial manifestation 2
  • Failure to consider COVID-19 delays isolation measures and increases transmission risk to healthcare workers 2
  • Chest imaging should be performed even in patients presenting primarily with abdominal complaints when COVID-19 is suspected 2

Special Populations

  • Elderly patients: laboratory tests may be nonspecific and normal despite serious infection; imaging is especially helpful in this population 1
  • Immunocompromised/neutropenic patients: typical signs of abdominal sepsis may be masked, diagnosis may be delayed, and mortality is high 1
  • Patients with obtunded mental status, spinal cord injury, or immunosuppression: maintain high suspicion for intra-abdominal infection when presenting with undetermined source of infection 1

Management Pitfalls

  • Do not delay imaging in hemodynamically stable patients without obvious peritonitis - CT provides definitive diagnosis 1
  • Do not delay antibiotics while awaiting imaging or culture results in septic patients 1
  • Fever may be absent in true infection, especially in elderly and immunocompromised patients 3
  • Use core temperatures rather than oral temperatures if concern for fever exists, as oral measurements have poor sensitivity 3

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

COVID-19 and Abdominal Pain

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

3
Research

Evaluation of fever in the emergency department.

The American journal of emergency medicine, 2017

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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