At a glance
Why get tested?
To identify whether you have the influenza (flu) virus
When to get tested?
To determine whether your flu-like symptoms are due to the influenza virus (and potentially which particular strain), or due to other causes
Usually a nose or throat swab
What is being tested?
Influenza (the flu) is a viral infection that tends to be seasonal, beginning in mid-late autumn and disappearing in spring. It is a common respiratory illness (affecting the lungs) that may cause headaches, fever, chills, muscle pains, exhaustion, a stuffy nose, sore throat, and a cough. Symptoms of flu tend to be more severe and longer lasting than the flu-like symptoms caused by the common cold. Flu and its complications can lead to hospitalisations or even death, especially in the very young, the elderly, and in those with lowered immune responses or pre-existing lung disease.
There are three overall types of influenza, known as A, B and C, each of which can change many times to create multiple strains (see Common questions#3). Influenza virus A is the most common and causes the most severe symptoms. Type B is less common and causes less severe symptoms, while type C usually causes only a mild illness (similar to the cold).
Flu testing relies on detecting virus (or its genetic material) that is being shed in the respiratory secretions of the person infected. Detectable virus is usually only shed for the first few days that someone is ill, so most testing must be done during this period. Anti-viral medications have been developed to treat influenza A and B. These medications, if given within 48 hours of the onset of symptoms, may reduce the severity of symptoms and reduce the time that a patient is sick by about a day. (Evidence suggests they will not usually help if given later and they will not work against other viruses or against bacterial infections).
These medications will only be prescribed if the person is at risk of complications and is known or suspected to have influenza A or B (e.g. while these are circulating in the community). For otherwise healthy people, the treatment is to stay in bed and rest, drinking plenty of fluids, until the symptoms have receded.
In the flu test, genetic material known as from the influenza virus is detected using a special technique known as (Polymerase Chain Reaction). In some cases, the influenza virus is actually grown and identified in the laboratory. The test will usually identify influenza A and B viruses and potentially a particular strain of influenza virus. It may be combined with tests for other viruses. This test is useful for documenting that the flu (A and/or B) has reached a community and for identifying outbreaks in particular populations, such as nursing homes, schools, or neighbourhoods. Identifying these outbreaks can assist healthcare workers in the prevention and treatment of the flu throughout a community and in the manufacture of the annual influenza vaccine.
How is the sample collected for testing?
A nasal swab is collected by having you tip your head back, then a swab (like a long cotton bud) is gently inserted into one of your nostrils until resistance is met (about 2.5 - 5 cm in), then rotated several times and withdrawn. This is not painful, but it may tickle a bit and cause your eyes to tear-up. Sometimes a throat swab may be taken.