In a patient with an acute upper respiratory infection, should testing for SARS‑CoV‑2 (COVID‑19), influenza A/B, and respiratory syncytial virus (RSV) be performed?

Testing for COVID-19, Influenza, and RSV in Upper Respiratory Infections

Yes, testing for SARS-CoV-2, influenza A/B, and RSV should be performed in patients with acute upper respiratory infections, as viral identification guides treatment decisions, reduces unnecessary antibiotic use, and improves clinical outcomes.

Recommended Testing Approach

For Symptomatic Patients

Use rapid multiplex testing (antigen or PCR) that detects all three viruses simultaneously 1. The evidence strongly supports this approach:

• Rapid antigen tests can be used as first-line testing with results in ~15 minutes, particularly when performed within 5 days of symptom onset 1
• If antigen test is negative but clinical suspicion remains high, confirm with NAAT (nucleic acid amplification test/PCR) 1
• Standard NAAT/PCR is preferred over rapid antigen testing when results can be obtained within 24 hours, as it offers superior sensitivity 1

Test Performance Considerations

The multiplex approach is highly effective:

• Sensitivity for triple antigen tests: 87-94% for SARS-CoV-2,79-96% for influenza A/B, and 86-95% for RSV when viral loads are adequate 2, 3, 4
• Specificity approaches 100% for all three viruses across platforms 2, 3
• Positive results have high predictive value and can guide immediate clinical decisions without confirmation 1

Specimen Collection

Throat swabs combined with nasal swabs provide optimal sensitivity (88% for SARS-CoV-2,100% for influenza) compared to nasopharyngeal swabs alone 5. This is particularly important as:

• Throat swabs alone detect SARS-CoV-2 (79%) and influenza (64%) more effectively than nasopharyngeal swabs
• Saliva has poor sensitivity (43% for SARS-CoV-2) and should be avoided 5

Clinical Impact and Rationale

Antimicrobial Stewardship

Positive viral testing significantly reduces inappropriate antibiotic use:

• Early viral diagnosis reduces odds of antibiotic prescribing by 85% (aOR 0.15,95% CI 0.08-0.28) 6
• 73% of patients with acute respiratory infections receive empirical antibiotics at admission, but viral identification allows de-escalation 6
• Multiplex testing identifies viruses in 46.5% of severe acute respiratory infections versus only 20% with routine single-pathogen testing 6

Hospital Resource Utilization

Rapid viral diagnosis leads to:

• Shorter hospital stays when positive results are obtained early 6
• More efficient triage in fever clinics and emergency departments 7
• Better infection control through prompt isolation decisions 7

Important Caveats

Test Limitations

1. Antigen test sensitivity decreases with lower viral loads: Sensitivity drops significantly at PCR Ct values >25-30 3, 8
2. Timing matters: Perform antigen testing within 5 days of symptom onset for optimal performance 1
3. False negatives occur: Always confirm negative antigen results with PCR when clinical suspicion remains high 1, 3

When to Confirm Negative Results

Confirm with NAAT/PCR when:

• Clinical suspicion for viral infection remains moderate to high
• Patient is immunocompromised or at high risk for severe disease
• Antiviral treatment decisions depend on the result
• Testing occurred >5 days after symptom onset

Practical Algorithm

Step 1: Perform rapid multiplex antigen test (COVID/Flu/RSV) at initial presentation if symptomatic

Step 2:

• If positive → Proceed with appropriate treatment/isolation; no confirmation needed
• If negative AND high clinical suspicion → Confirm with multiplex PCR
• If negative AND low clinical suspicion → Clinical management based on presentation

Step 3: For PCR testing, use combined throat + nasal swab for optimal sensitivity 5

The evidence demonstrates that multiplex respiratory viral testing in upper respiratory infections improves diagnostic accuracy, reduces antibiotic overuse, and enhances clinical outcomes—making it a standard of care rather than an optional test 6, 9, 7.