What is the most likely diagnosis and appropriate initial management for a 45‑year‑old woman with a one‑day history of headache, nausea, diarrhea, bloating, non‑productive cough, and yellow foul‑smelling stools, without chronic illness, medication use, recent travel, or exposures?

Acute Gastroenteritis with Consideration for COVID-19

This presentation is most consistent with acute viral gastroenteritis, and initial management should focus on oral rehydration and symptomatic care, with COVID-19 testing warranted given the combination of gastrointestinal and respiratory symptoms.

Most Likely Diagnosis

Acute viral gastroenteritis is the most probable diagnosis in this 45-year-old woman presenting with one day of headache, nausea, diarrhea, bloating, and non-productive cough 1, 2. The yellow foul-smelling stools suggest malabsorption or rapid transit typical of viral enteritis 1. However, the constellation of GI symptoms combined with cough raises important consideration for COVID-19, which presents with GI manifestations in 11-37% of cases 1.

Key Diagnostic Considerations

• Viral gastroenteritis accounts for the majority of acute diarrheal illness in adults, with norovirus being the leading pathogen (58% of cases) 1
• COVID-19 should be strongly considered given that 21 patients in one cohort lacked respiratory symptoms entirely and presented only with GI symptoms 1
• The presence of diarrhea with cough in COVID-19 patients is associated with significantly worse outcomes, including 2.75 times higher mortality risk 3
• Yellow foul-smelling stools without blood make bacterial dysentery (Shigella, Campylobacter) or inflammatory causes less likely 1

Initial Assessment Priorities

Clinical Evaluation

Assess for dehydration severity by examining:

• Vital signs focusing on orthostatic changes, tachycardia, and blood pressure 1
• Mucous membrane moisture, skin turgor, and mental status 1
• Urine output and concentration 1

Screen for inflammatory/invasive features:

• Fever >38.5°C suggests bacterial or severe viral illness 1
• Blood in stool would indicate inflammatory diarrhea requiring different management 1
• Severe abdominal pain out of proportion to exam findings could suggest ischemia 4

Measure oxygen saturation at rest - this is the single most important vital sign if COVID-19 is suspected, as SpO₂ <93% defines moderate-to-severe disease 5

Laboratory Testing Strategy

Most patients with acute watery diarrhea do NOT require laboratory workup 1, 2. However, testing is indicated if:

• Fever with bloody diarrhea is present 1
• Symptoms persist beyond 7 days 1, 6
• Severe dehydration or immunosuppression exists 1, 2
• COVID-19 is suspected based on epidemiologic or clinical factors 5, 7

If testing is warranted, obtain:

• COVID-19 RT-PCR testing given the combination of GI and respiratory symptoms 1, 5, 7
• Complete blood count if systemic illness is suspected 4
• Stool studies are NOT indicated for simple acute watery diarrhea without fever or blood 1, 2

Initial Management

Rehydration Therapy

Oral rehydration solution (ORS) is first-line therapy for mild to moderate dehydration 1. This patient should:

• Receive reduced-osmolarity ORS as the primary intervention 1
• Resume normal age-appropriate diet immediately after rehydration 1
• Continue oral intake throughout the illness 1

Intravenous fluids (lactated Ringer's or normal saline) are reserved for severe dehydration, shock, altered mental status, or failure of oral rehydration 1

Symptomatic Management

Antimotility agents (loperamide) may be offered to this immunocompetent adult with watery diarrhea 1. However:

• Avoid if fever develops or bloody stools appear 1
• Do not use as substitute for rehydration 1

Antiemetics (ondansetron) can facilitate oral rehydration if nausea is prominent 1

Probiotics may be offered to reduce symptom duration and severity 1

Antibiotic Therapy

Empiric antibiotics are NOT indicated for this presentation 1, 2. Antibiotics should only be considered if:

• Fever with bloody diarrhea develops (suggesting Shigella, Campylobacter, or Salmonella) 1
• A specific bacterial pathogen is identified on stool culture 1
• The patient becomes severely ill or immunocompromised 1, 2

COVID-19 Specific Considerations

When to Test for COVID-19

COVID-19 testing is warranted in this case because 1, 5, 7:

• GI symptoms (diarrhea, nausea) occur in 11-37% of COVID-19 patients 1
• Diarrhea was present on admission in 6-37% of hospitalized COVID-19 patients 1
• Non-productive cough combined with GI symptoms is a recognized COVID-19 presentation 1
• Patients with GI symptoms may lack typical respiratory symptoms initially 1

Risk Stratification if COVID-19 Confirmed

Monitor closely for disease progression if COVID-19 is confirmed 5:

• Serial oxygen saturation measurements (SpO₂ <93% indicates moderate-to-severe disease) 5
• Respiratory rate assessment (tachypnea suggests respiratory distress) 5
• Consider inflammatory markers (CRP, D-dimer) if admission is being considered 5

Diarrhea in COVID-19 patients predicts worse outcomes 3:

• 2.75 times higher mortality risk 3
• 2.24 times higher ICU admission rate 3
• 3.16 times higher intubation risk 3

Disposition and Follow-Up

Outpatient Management

Most patients can be managed at home if 1, 2:

• Mild dehydration that responds to oral rehydration 1
• No fever or bloody stools 1
• Adequate social support and ability to maintain hydration 1
• Normal oxygen saturation if COVID-19 is suspected 5

Provide clear return precautions:

• Worsening symptoms beyond 48-72 hours 1, 6
• Development of fever, bloody stools, or severe abdominal pain 1
• Inability to maintain hydration 1
• Shortness of breath or chest pain if COVID-19 is possible 5, 7

Hospital Admission Criteria

Admit if 1, 4:

• Severe dehydration unresponsive to oral rehydration 1
• Altered mental status or shock 1
• Persistent symptoms >20 days in any patient 4
• SpO₂ <93% on room air if COVID-19 is confirmed 5
• Immunosuppression with persistent GI symptoms 4

Critical Pitfalls to Avoid

• Do not dismiss the combination of GI and respiratory symptoms as simple gastroenteritis without considering COVID-19 1, 7
• Do not order routine stool cultures for acute watery diarrhea without fever or blood 1, 2
• Do not prescribe empiric antibiotics for uncomplicated acute watery diarrhea 1, 2
• Do not use antimotility agents if fever or bloody stools develop 1
• Do not rely on symptoms alone to assess COVID-19 severity; measure oxygen saturation objectively 5
• Do not overlook that COVID-19 patients with diarrhea have significantly worse outcomes and may require closer monitoring 3