1. Basic Facts About Influenza
What Is Influenza?
Influenza, commonly referred to as the flu, is a contagious viral infection caused by the influenza A or B viruses. The illness is associated with the upper respiratory system, and symptoms range from mild to severe. It is considered to be most dangerous among the elderly, young children and others with inhibited or weak immune systems due to the significant toll infection can take on the body. Outbreaks of influenza are considered to be seasonal, with the highest number of cases occurring during the winter. Both the influenza A and B viruses typically cause the annual epidemics experienced every winter in the United States. The influenza A virus can be divided by subtype depending on the arrangement of two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N).1 During the past 40 years, the most common influenza A viruses circulating globally are influenza A (H1N1), influenza A (H3N2) and influenza B.
Unlike other illnesses associated with symptoms that occur gradually, symptoms attributed to the flu often begin simultaneously and suddenly for individuals who have recently been infected.2 The influenza virus begins by infecting the nose, throat and sometimes the lungs. It moves to other parts of the body, causing muscle soreness, fatigue and headaches. Fever is common, with temperatures often over 38°C, although this does not occur in all cases.3 Other common influenza symptoms include:
- Stuffy or runny nose
- Severe fatigue or inhibited levels of energy
- Chills or sweats
- Muscle aches or body soreness
- Coughing, sore throat, raspy voice
The influenza virus should not be confused with the illness commonly referred to as the stomach flu, which is usually caused by norovirus. The stomach flu results in symptoms such as vomiting or diarrhea which are not commonly associated with an influenza virus.
How Long Does the Flu Last?
In normally healthy people, symptoms often last between five and seven days.4 The severity of these symptoms can take a dramatic toll on one’s ability to do work or everyday tasks, often requiring infected people to take time off of work to rest and recover. Healthy adults are usually able to fully recover from influenza symptoms in about a week. Symptoms may be more severe in young children, those over 65, pregnant women and those with chronic illnesses or compromised immune systems (such as diabetes, HIV and heart disease) and may be associated with complications such as pneumonia and longer recovery times.
lnfluenza Incubation Period
The incubation period for an illness is the time that elapses between first exposure and the appearance of symptoms. While the incubation period for influenza varies, one to four days is typical, with most adults averaging two days.5 During this time people who have been exposed and infected with the virus can still pass it on to others before experiencing symptoms themselves.
Who ls at Risk?
Like other highly contagious illnesses, influenza is a threat to anyone who is regularly exposed to other people in the workplace, healthcare facilities, schools and colleges, malls, theaters, or on public transport systems. Although the elderly, young children and people with weakened immune systems are most at risk for severe or deadly symptoms, healthy adults can miss days or weeks of work when infected. Due to the seriousness and potential severity of influenza’s symptoms, everyone should take extra precautions during the flu season to prevent the spread of the virus.
How ls lnfluenza Diagnosed?
Diagnostic tests are available for the influenza virus. Methods of testing include viral culture, rapid antigen testing, reverse transcription polymerase chain reaction and rapid molecular assays.6 Diagnostic tests are most valuable for determining whether influenza is the cause of an illness outbreak in closed settings such as schools, hospitals, cruise ships, long-term care facilities or other institutional facilities. However, diagnostic tests are not always performed on an individual basis when influenza is suspected, given that the symptoms are common to other illnesses and the treatment is similar for multiple strain types. When a test is performed, the doctor will most likely use a swab to take a sample from the back of the nose or throat to test for the presence of influenza A antigens.4
For many healthy adults experiencing symptoms commonly associated with the flu, doctors will simply recommend bed rest and hydration. During this period, it is recommended that individuals limit or prevent exposing themselves to others to decrease the likelihood of transmission. Rest is also crucial during this period to allow the immune system to fight the influenza virus.
When complications associated with influenza are a concern, antiviral medication may be prescribed. These can shorten the illness by a day or two, and can help reduce the risk of the development of other potentially dangerous complications. The most common medications prescribed include oseltamivir (Tamiflu®) and zanamivir (Relenza®).4