What laboratory tests can be used to confirm the diagnosis of influenza?
Appropriate samples to collect can include a nasopharyngeal or throat swab, from adults or nasal wash, or nasal aspirates, depending on which rapid test is used. Samples should be collected within the first 4 days of illness. Rapid influenza tests provide results within 24 hours; viral culture provides results in 3-10 days. Most of the rapid tests are approximately >70% sensitive for detecting influenza and approximately >90% specific. Because as many as 30% of samples that would be positive for influenza by viral culture may give a negative rapid test result, negative rapid tests should be followed by viral culture in a sub-sample of the swabs collected. Viral culture can also identify other causes of influenza-like illness when influenza is not the cause. Serum samples can be tested for influenza antibody to diagnose acute infections. Two samples should be collected per person: one sample within the first week of illness and a second sample 2-4 weeks later. If antibody levels increas
