Influenza (flu) is a contagious respiratory illness caused by influenza viruses. Influenza viruses infect the nose, throat, and sometimes the lungs, it can cause mild to severe illness. The infection usually lasts for about a week. It is characterized by sudden onset of high fever, myalgia, headache and severe malaise, non-productive cough, sore throat and rhinitis. Most people recover within one to two weeks without requiring any medical treatment. In the very young, the elderly and people suffering from medical conditions, such as lung diseases, diabetes, cancer, kidney or heart problems, influenza poses a serious risk. In these people, the infection may lead to severe complications of underlying diseases, pneumonia and death. The best way to prevent the flu is by getting vaccinated each year. According to the American Academy of Pediatrics, a flu vaccine once a year cuts the risk of getting the flu by 95%.
The currently circulating influenza viruses that cause human diseases are divided into two groups: A and B. Influenza A has two subtypes which are important for humans: A(H3N2) and A(H1N1), of which to former is currently associated with most deaths. Influenza viruses are defined by two different protein components, known as antigens, on the surface of the virus. They are spike-like features called haemagglutinin (H) and neuraminidase (N) components.
The genetic makeup of influenza viruses allows frequent minor genetic changes, known as antigenic drift, and these changes require annual reformulation of influenza vaccines.
The virus is easily passed from person to person through the air by droplets and small particles excreted when infected individuals cough or sneeze. The influenza virus enters the body through the nose or throat. It then takes between one or four days for the person to develop symptoms. Someone suffering from Influenza can be infectious from the day before they develop symptoms until seven days afterwards.
Diseases spreads very quickly among the population, especially in crowded circumstances. Cold and dry weather enables the virus to survive longer outside the body than in other conditions and, as a consequence, seasonal epidemics in temperate areas appear in winter.
Seasonal influenza is characterized by a sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and a runny nose. The cough can be severe and can last two or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention. But influenza can cause severe illness or death, especially in people at high risk.
While the illness ranges from mild to severe and even death, hospitalization and death occur mainly among high risk groups. Worldwide, these annual epidemics are estimated to result in about 3 to 5 million cases of severe illness, and about 290,000 to 650,000 deaths
|Symptom||Common Cold||Influenza (Flu)|
|Fever||Fever may be present, but is usually not very high, or there may be a later or gradual onset of fever that comes and goes. Children usually have higher fevers than adults||High fever of up to 40 degrees Celsius for about 2-4 days|
|Aching body and muscles||Pain may be mild or non-existent||Intense and frequent pain and achiness in the body, joints and muscles|
|Headache||Pain may be mild or non-existent.||Intense headaches|
|Weakness and fatigue||Uncommon, may be just some feelings of irritation or discomfort||Moderate to extreme fatigue that may last for 2-3 weeks|
|Chest tightness or coughing||Dry and fairly infrequent coughing||Common and can become very severe|
|Loss of appetite||Can eat normally||Commonly involves symptoms of loss of appetite|
|Chills and sweats||Uncommon||Common|
|Nausea and vomiting||Uncommon||May occur in some cases, especially in child patients|
Complications of flu can include bacterial pneumonia, ear infections, sinus infections, and worsening of chronic medical conditions, such as congestive heart failure asthma or diabetes
Anyone, even healthy people, can get the flu, and serious problems related to the flu can happen at any age. Yet some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women and young children.
The first and most important step in preventing flu is to get a flu vaccination each year. You can also protect yourself by taking preventive action.
Certain preventive actions – like covering your cough and frequent hand washing – can help keep germs from spreading.
Protect yourself and your infant by routinely taking these actions:
M.D., Faculty of Medicine, Siriraj Hospital, Mahidol University, 1966 , 2017