Can a positive SARS-CoV-2 (COVID-19) swab also indicate influenza (flu) infection?

COVID-19 Swabs and Influenza Detection

A positive COVID-19 test (SARS-CoV-2) does not indicate influenza infection, as these are separate viruses requiring different specific tests for detection. While co-infection with both viruses is possible, a single COVID-19 swab test cannot detect influenza.

Diagnostic Testing for COVID-19 vs. Influenza

• COVID-19 tests specifically detect SARS-CoV-2 genetic material or antigens
• Influenza tests specifically detect influenza A or B genetic material or antigens
• Each test is designed to identify a specific pathogen, not multiple pathogens simultaneously

Co-infection Evidence and Prevalence

The prevalence of co-infection with both SARS-CoV-2 and influenza is relatively low:

• Meta-analysis data shows overall co-infection rate of only 0.7% (95% CI = 0.4-1.3%) 1
• Co-infection rates are higher in children (3.2%) compared to adults (0.3%) 1
• Most influenza co-infections (74.4%) are due to influenza A virus 1
• Co-infected patients may experience more severe clinical conditions than those with SARS-CoV-2 alone 2

Testing Recommendations

• Separate testing for each virus is required for accurate diagnosis
• During respiratory virus seasons, consider testing for both pathogens, especially in:
  • Patients with severe respiratory symptoms
  • High-risk patients (elderly, immunocompromised, those with comorbidities)
  • Healthcare settings where treatment decisions depend on specific diagnosis

Clinical Implications of Co-infection

• Co-infection can lead to more severe clinical presentation 2
• Patients with both viruses may require specific treatments for each infection
• Oseltamivir may be appropriate for confirmed influenza component of co-infection 3
• Antibiotics should not be routinely prescribed for COVID-19 patients unless bacterial infection is suspected 4

Common Pitfalls to Avoid

1. Assuming a positive COVID-19 test rules out influenza - These are separate tests detecting different viruses
2. Missing co-infections - During influenza season, consider testing for both pathogens in patients with respiratory symptoms
3. Inappropriate antibiotic use - Antibiotics should not be routinely prescribed for viral infections unless bacterial co-infection is suspected 4
4. Neglecting vaccination - Influenza vaccination remains important to reduce the risk of co-infection 4

In cases where co-infection is suspected, comprehensive diagnostic testing for both viruses should be performed to guide appropriate treatment decisions and improve patient outcomes.