Key Symptoms to Differentiate COVID-19 and Influenza
The most important symptoms to assess when differentiating between COVID-19 and influenza are fever, cough, dyspnea, fatigue, and most distinctively, sudden loss of taste (ageusia) and smell (anosmia), which are stronger predictors of COVID-19 than self-reported fever. 1
Common Symptoms in COVID-19
Primary Respiratory Symptoms
- Fever (92.8% of patients) - typically the most common symptom 1
- Cough (69.8% of patients) - typically dry in nature 1
- Dyspnea/shortness of breath (34.5% of patients) - associated with severe COVID-19 (OR 2.43) 1, 2
- Sputum production/expectoration (25.8% of patients) 3
Distinctive COVID-19 Symptoms
- Sudden gustatory dysfunction/ageusia (88.8% of patients) 1
- Sudden olfactory dysfunction/anosmia (85.6% of patients) 1
- These sensory symptoms are stronger predictors of COVID-19 than fever 1
Other Common Symptoms
- Fatigue (38.5% of patients) 1, 3
- Myalgia/muscle pain (27.7% of patients) 1
- Headache (7.2% of patients) 1
- Gastrointestinal symptoms including diarrhea (6.1% of patients) 1
- Sore throat (5.1% of patients) 1
- Rhinorrhea/runny nose (4.0% of patients) 1
Differentiating COVID-19 from Influenza
Key Differentiating Factors
- Loss of taste and smell are significantly more common in COVID-19 than influenza 1
- COVID-19 shows lower frequency of leukocytosis, neutrophilia, and lymphocytopenia compared to influenza 4
- COVID-19 patients more frequently have elevated creatine kinase levels 4
Radiological Differences
- While both infections can cause similar pulmonary lesion locations, COVID-19 presents with more diverse CT features 4
- COVID-19 shows significantly more:
- Consolidation patterns
- Crazy paving pattern
- Rounded opacities
- Air bronchogram
- Tree-in-bud sign
- Interlobular septal thickening
- Bronchiolar wall thickening 4
Disease Severity Assessment for COVID-19
- Mild cases (81%): Non-pneumonia and mild pneumonia 1
- Severe cases (14%): Dyspnea, respiratory frequency ≥30/min, blood oxygen saturation ≤93%, PaO2/FiO2 ratio <300, and/or lung infiltrates >50% within 24-48 hours 1
- Critical cases (5%): Respiratory failure, septic shock, and/or multiple organ dysfunction or failure 1
Special Considerations
Pediatric Presentation
- Children may present with fever, fatigue, cough, nasal congestion, runny nose, expectoration, diarrhea, and headache 1
- As disease progresses: dyspnea, cyanosis, malaise, poor feeding, reduced activity 1
- Children often have milder clinical presentations than adults 1
Co-infection Possibility
- COVID-19 and influenza co-infection is rare (reported rate of 0.54%) but possible 5
- Co-infection may be underdiagnosed unless specific screening is performed 5
Clinical Pitfalls to Avoid
- Do not rely solely on fever for diagnosis, as ageusia and anosmia are stronger predictors of COVID-19 1
- Do not dismiss COVID-19 in patients with minimal respiratory symptoms, as presentation can vary widely 1
- Remember that asymptomatic COVID-19 infection is possible, especially in children 1
- Do not overlook the possibility of co-infection with both COVID-19 and influenza, especially during flu season 5