From the Research
The flu swab result should be considered negative, as the delayed appearance of a test line after an hour is likely an artifact rather than a true positive result. When a flu swab initially reads as negative and then shows a test line after sitting for an hour, this delayed reaction should not be interpreted as a positive result. Rapid influenza diagnostic tests (RIDTs) have specific time windows for reading results, typically 10-15 minutes after sample application, as indicated in the test instructions. Reading the test outside this designated timeframe can lead to false results due to sample drying, reagent deterioration, or non-specific binding that occurs over time. These delayed lines are considered artifacts rather than true positive results.
Key Considerations
- The diagnosis of influenza is typically made clinically, and laboratory confirmation is not necessary for most patients in the outpatient setting 1.
- Rapid molecular assays are the preferred diagnostic tests because they can be done at the point of care, are highly accurate, and have fast results 1.
- If clinical suspicion for influenza remains high despite a negative rapid test, consider confirmatory testing with more sensitive methods like PCR, or treat empirically based on clinical judgment, especially during peak flu season or if the patient is at high risk for complications.
Management Options
- Consider treating the patient empirically with anti-influenza drugs if they present within 48 hours of symptom onset, as this can decrease the duration of illness and reduce the risk of serious complications 1.
- Annual influenza vaccination is recommended for all people six months and older who do not have contraindications 1.
- The use of antiviral medications such as zanamivir, oseltamivir, laninamivir, and baloxavir can reduce symptomatic seasonal influenza in persons exposed to influenza 2.