Recommended Diagnostic Testing and Treatment for Influenza
Rapid molecular assays (nucleic acid amplification tests) are the preferred diagnostic tests for influenza, and treatment with antiviral medication should be initiated as soon as possible after symptom onset without waiting for test results in high-risk patients.
Diagnostic Testing Recommendations
Preferred Testing Methods
- Rapid molecular assays (nucleic acid amplification tests) are the first-line diagnostic test for influenza due to their high sensitivity (86-100%) and specificity, with results available in under 20 minutes 1, 2
- RT-PCR is recommended for hospitalized patients to improve detection of influenza virus infection 1
- Nasopharyngeal specimens are preferred over other upper respiratory tract specimens to maximize detection 1
Testing Approach Based on Clinical Setting
Outpatient setting:
Hospitalized patients:
- Use RT-PCR or other molecular assays rather than RIDTs or immunofluorescence assays 1
- For patients with respiratory failure on mechanical ventilation, collect endotracheal aspirate or bronchoalveolar lavage fluid 1
- Consider multiplex RT-PCR assays targeting multiple respiratory pathogens in immunocompromised patients 1
Important Testing Considerations
- Do not use RIDTs in hospitalized patients except when molecular assays are unavailable 1
- Negative RIDT results should be confirmed with RT-PCR due to suboptimal sensitivity 1
- Do not collect or test specimens from non-respiratory sites (blood, CSF, urine, stool) 1
- Do not use serological testing for diagnosis of seasonal influenza 1
Treatment Recommendations
Antiviral Therapy
- Initiate antiviral treatment as soon as possible after illness onset, ideally within 24 hours of symptom onset 1, 3
- Do not delay treatment while waiting for test results, especially in high-risk patients 1
- Treatment provides greatest benefit when started within 24 hours of symptom onset 4
- FDA-approved options include oseltamivir, zanamivir, peramivir, and baloxavir marboxil
Treatment Considerations
- Oseltamivir reduces median time to improvement by 1.3 days in adults with influenza 3
- Antiviral treatment decreases duration of illness by about 24 hours in otherwise healthy patients 4
- Early antiviral therapy is associated with reduced antibiotic use and fewer ICU admissions 5
Clinical Approach Algorithm
During influenza season:
- Assess for influenza-like symptoms (fever, cough, chills/sweats, myalgias, malaise)
- Consider influenza in patients with respiratory symptoms or fever during influenza season, even without typical influenza-like illness 1
Diagnostic testing decision:
- For outpatients: Use rapid molecular assays if available
- For hospitalized patients: Use RT-PCR or molecular assays
- For immunocompromised patients: Use multiplex RT-PCR assays
Treatment decision:
- Initiate antiviral therapy immediately in high-risk patients without waiting for test results
- For non-high-risk patients presenting within 48 hours of symptom onset, consider antiviral therapy
- Select appropriate antiviral based on patient factors, local resistance patterns, and drug availability
Common Pitfalls to Avoid
- Relying solely on clinical diagnosis during periods of low influenza activity 6
- Delaying antiviral treatment while waiting for test results 1
- Using RIDTs as the only diagnostic test in hospitalized patients 1
- Assuming a negative RIDT rules out influenza infection 1
- Collecting specimens from non-respiratory sites 1
- Using serological testing for acute diagnosis 1
By following these evidence-based recommendations, clinicians can improve diagnostic accuracy and ensure timely, appropriate treatment for patients with influenza.