How is Influenza Diagnosed

Preferred respiratory samples for influenza testing include nasopharyngeal or nasal swab, and nasal wash or aspirate, depending on which type of test is used (see table). Samples should be collected within the first 4 days of illness. Rapid influenza tests provide results within 30 minutes or less; viral culture provides results in 3-10 days. Most of the rapid tests that can be done in a physician's office are approximately greater than 70% sensitive for detecting influenza and approximately greater than 90% specific. Therefore, false negative results are more common than false positive results, especially during peak influenza activity.

During outbreaks of respiratory illness when influenza is suspected, some respiratory samples should be tested by both rapid tests and by viral culture. The collection of some respiratory samples for viral culture is essential for determining the influenza A subtypes and influenza A and B strains causing illness, and for surveillance of new strains that may need to be included in the next year's influenza vaccine. During outbreaks of influenza-like illness, viral culture also can
help identify other causes of illness.

Mainly nasal swabs and naval washes are used in testing through bronhials etc.


Content Source: Coordinating Center for Infectious Diseases (CCID)
National Center for Immunization and Respiratory Diseases (NCIRD)