5 Diagnosis of influenza
Many diseases produce symptoms similar to those of influenza; in fact, ‘flu-like’ is a term that is frequently used to describe several different illnesses. Since influenza spreads rapidly by airborne transmission and is a life-threatening condition in certain vulnerable groups, it is important that cases of the disease are identified as quickly as possible, so that preventative measures may be taken.
Most viral infections are not treated, although antiviral drugs such as zanamivir are used for potentially life-threatening cases or where the risk of transmission is high (as occurs during a pandemic).
Which sites in the body should be sampled for diagnosis?
The influenza virus infects the respiratory tract and is spread by coughing and sneezing, so specimens should be taken from the nose, throat or trachea.
In practice, the best specimens are nasal aspirates or washes, but swabs of the nose or throat may be used if they are taken vigorously enough to obtain cells. Ideally, samples should be taken within three days of the onset of illness, and all specimens need to be preserved in a transport medium and kept chilled until they reach the clinical microbiology laboratory.