From the Guidelines
During peak influenza season, ICU patients with influenza-like illness and a negative rapid influenza antigen test should be empirically treated with neuraminidase inhibitors such as oseltamivir (Tamiflu) while awaiting more sensitive confirmatory testing. The recommended dosage for adults is 75 mg twice daily for 5 days, with dose adjustments for renal impairment, as suggested by 1. Treatment should be initiated as soon as possible, ideally within 48 hours of symptom onset, without waiting for confirmatory test results. This approach is necessary because rapid influenza tests have limited sensitivity, leading to frequent false negatives, especially early in the illness, as noted in 1. More sensitive molecular tests like RT-PCR should be ordered simultaneously. The benefits of early antiviral treatment include reduced viral shedding, shortened illness duration, decreased risk of complications, and potentially reduced mortality in critically ill patients. Key considerations in making this decision include:
- The high prevalence of influenza in the community during peak season
- The limited sensitivity of rapid influenza antigen tests
- The potential for false-negative results, especially in critically ill patients
- The importance of early antiviral treatment in reducing morbidity and mortality
- The need for more sensitive confirmatory testing, such as RT-PCR, to guide treatment decisions, as recommended in 1. By empirically treating ICU patients with influenza-like illness and a negative rapid influenza antigen test, clinicians can balance the minimal risks of unnecessary treatment against the significant risks of delayed treatment in critically ill patients, ultimately improving outcomes in terms of morbidity, mortality, and quality of life.
From the Research
Strategy to Avoid False-Negative Cases
To avoid false-negative cases in ICU patients with an influenza-like illness and a negative rapid influenza antigen test during peak influenza season, the following strategies should be considered:
- Empiric antiviral therapy should be initiated regardless of the results of rapid antigen testing, as delayed treatment can lead to severe disease and poor outcomes 2, 3, 4, 5
- Confirmatory reverse transcriptase polymerase chain reaction (RT-PCR) should be performed to confirm the diagnosis of influenza, especially in patients with a high risk of complications or severe disease 3
- Influenza testing and empiric infection control precautions should be considered in patients admitted during influenza season with a diagnosis of pneumonia or respiratory infection, regardless of fever status 4
- Patients with a negative rapid influenza antigen test should be treated as if they have influenza, especially during peak influenza season, due to the high risk of false-negative results 3, 5
Key Considerations
- The sensitivity of rapid antigen detection for influenza is generally low, which can lead to false-negative results 3
- Delayed antiviral treatment can result in severe disease and poor outcomes, especially in high-risk patients 2, 4, 5
- Empiric antiviral therapy and infection control precautions can help prevent severe disease and transmission of influenza in ICU patients 3, 4