Diagnosis of Flu

Nasopharyngeal swab. These are done using two special swabs to collect samples from the nose and throat; they do not cause any damage, but the swabs may tickle and make you want to sneeze. A very thin swab is inserted in a nostril and rotated three times to collect as many cells as possible. A second, slightly thicker swab is used to collect a sample from the throat following the same procedure of wiping the swab three times to try and gather the maximum number of cells.

Nasal lavage. This technique is used in small children because it is straightforward and easy to do. The sampling method uses a syringe to flush 1–1.5 mL of sterile saline solution into one nostril while holding the other closed. Suction is then applied to the syringe to recover the saline solution and nasal discharge. The sample is sent to a laboratory in a container filled with a special culture media for viruses to maintain sample quality.

Bronchoalveolar lavage. This method is carried out in patients in the Intensive Care Unit.

Virus isolation. This involves cultivating the respiratory sample and isolating the virus.

Detection of viral proteins. These tests entail binding antibodies with proteins on the virus. If viral proteins are detected in the respiratory sample, it confirms the patient has influenza.

Detection of viral genetic material. Tests called molecular assays are used to extract any viral genetic material present in respiratory samples. In this case, if viral ribonucleic acid (RNA) is isolated from the patient’s sample, it confirms the presence of the flu virus.