Influenza is an infectious viral disease that affects nose, throat, and lungs. It is contagious and often occurs as an epidemic. Commonly known as the flu, influenza is an airborne disease and spreads through droplets when the infected person coughs or sneezes.
The droplets fall on the face of a person nearby, who gets infected. Touching an object or a surface that has flu virus may also result in spreading of the disease.
This often occurs when the person touches face, particularly nose, mouth and eyes after touching the surface. Direct contact with the infected person, as in shaking hands, also leads to the spread of influenza.
There are three different types of flu viruses – influenza A, influenza B, and influenza C. Epidemics are caused by type A and B. Flu caused by type C is a mild respiratory illness.
Type C does not cause epidemics. Manifestations of influenza may range from mild fatigue to severe respiratory illness. A Severe form of flu is potentially life-threatening leading to respiratory failure and even death.
Reports show that influenza causes more than 20,000 deaths annually all over the world. Death due to flu is more common among infants and elderly people.
In some people, vomiting and diarrhea are also seen as symptoms. Some others may not have a fever as such, but may feel feverish or chillness. Muscle pain is also a common complaint in people with this infection.
The symptoms of the flu may start appearing in 1-4 days after the exposure to the virus.One can spread the infection to another person, one to two days before the onset of symptoms. Thus, even before one is aware of the infection, he/she may spread it to others.
Influenza virus can infect people of any age group, but some are at a high risk of developing the infection. This includes people above 65 years of age, infants and young children.
Other people who are at high-risk include:
Pregnant women
People with chronic medical conditions like asthma, kidney disease, and diabetes
People with weak immune system
Obese people with BMI higher than 40
People in nursing homes
People in care facilities
Symptoms of flu may remain mild, but medical attention is required for elderly people.
Vaccination is the best way to prevent the flu. Vaccines are of two types – nasal spray vaccine and flu shot. The flu shot is recommended for anybody over 6 months. Annual flu vaccinations are given in September and continued for some time through the year.
Influenza is diagnosed by flu tests. The most common diagnostic test used for influenza is rapid influenza diagnostic test. Treatment for flu is symptomatic using painkillers. A person with the flu should stay back at home and have ample rest.
Influenza is caused by infection of any of the three types of influenza virus A, B or C. influenza A is more pathogenic when compared to the other two types. The virus spreads through tiny droplets of a sneeze or a cough that spreads in the air when an infected person sneezes or coughs.
The tiny droplets with viruses land on the mouth, nose or face of another person and cause infection. It may also spread by touching a surface with the flu virus and then touching the face, particularly mouth, eyes or nose.
Once exposed to the virus, the symptoms may start appearing within an average of two days. But an infected person may spread the disease to another person one to two days before the onset of the typical symptoms. The person may remain contagious for about 5-7 days after becoming sick with an infection. Some people may be able to spread the infection for a longer time.
In tropical countries, influenza infection occurs throughout the year. In Northern hemisphere, the infection starts in autumn and peaks during mid-February. It may continue until late spring. The duration and severity of the influenza epidemic depend on the subtype of virus involved in the condition.
The viruses are constantly mutating or changing, resulting in the appearance of new strains periodically. When exposed to a strain of influenza virus, our body makes antibodies against the virus fight against invasion.
When exposed to the same strain or a similar strain, at a later stage, the antibodies help to prevent infection. It will also help to reduce the severity of the infection. But these antibodies are unable to protect the body against infection from the new strains of viruses formed by mutation.
The immunological differences in the subtypes of viruses are the reason for the inability of antibodies to launch an attack.
A number of factors are known to increase the chance of getting influenza virus infection, includes:
Age – influenza virus infection is found to be more among young children and elderly people.
Weakened immunity -- procedures and disease conditions that weaken the immune system like radiation therapy, chemotherapy, drugs that prevent graft rejection, corticosteroids, and HIV/AIDS infection increase the susceptibility of infection by these viruses. It may also increase the risk of developing complications due to influenza.
Living conditions – living in nursing homes or long-term care facilities with many other residents is another risk factor for catching influenza virus infection.
Chronic conditions – Many chronic diseases like cardiac problems, diabetes, and asthma are known risk factors for influenza.
Pregnancy – the risk of flu is more during the second and third trimesters of pregnancy. They may also develop complications from influenza infections during this period. The risk is found to be more among women who are two weeks into postpartum.
BMI above 40 – obese people with a BMI above 40 have increased the risk of infection and complication due to flu.
3 Diagnosis and Treatment
The most common test used in the diagnosis of influenza is rapid influenza diagnostic test. Results of this test are obtained within half an hour aiding early diagnosis. In some cases, the test may turn negative even when the person has an infection.
More sensitive and accurate diagnostic tests are now available for diagnosis. For this diagnostic test, the doctor takes a swab from the back of the throat or inside of the nose which is then analyzed.
Blood samples are generally not taken for diagnosis of influenza. Rapid tests are more accurate in detecting infection in children. Tests may vary greatly in the ability to detect infection. But, during an epidemic, a positive test for influenza should be taken seriously.
In some cases, even in the presence of flu-like symptoms doctor may not recommend rapid flu test for diagnosis. This is because the treatment may continue even if the test is positive or negative.
The diagnosis may be based on symptoms and physical examination. Testing is helpful in case of people who are at high risk of influenza infection in pregnant women, patients with weakened immune system, and people with chronic illnesses. This diagnosis will help the doctor to make an appropriate decision about the type of care to be extended to the patient.
The major indicators of influenza are high fever, chills or feverishness, headache, body pain, fatigue, nausea, vomiting, diarrhea and cold sweats. A runny nose, cough, and sneezing are also common symptoms. These symptoms are the main diagnostic features for influenza.
In most of the cases, adequate rest and plenty of water will help in alleviating the symptoms of flu. In some cases, antiviral medications are recommended. This includes oseltamivir and zanamivir.
These medications are useful in reducing the duration of the condition by a day or two. Further, it also helps in preventing complications associated with the condition. Antiviral medications are taken orally or inhaled.
Inhaler form of antiviral medications is not suggested for people with respiratory diseases like asthma and lung disease. Antiviral medications have side effects like nausea and vomiting. In teenagers, this is associated with more serious effects like delirium and self-harm behavior.
Flu vaccines are usually recommended for prevention of influenza, particularly in places where outbreaks are noted. The annual vaccine is suggested for anybody above six months of age.
The vaccination takes two weeks for the protective effect to begin. Vaccinations prevent infection and also complications associated with influenza.
Flu vaccines are not suggested for people who are allergic to chicken eggs, children under six months of age, people who have a fever and those who had a reaction to vaccination in the past. If pregnant women are given flu shot during pregnancy, the infants have less risk of getting the infection.
Pain killers are effective in controlling symptoms like muscle pain, body aches and headaches associated with the flu. People with infection should try to avoid contact with other people.
Taking plenty of liquids, getting good sleep or rest, avoiding alcohol and smoking, and keeping warm are the typical home remedies for flu. The doctor should be informed of the condition if the person is at high risk of flu infection. Decongestants will help in opening the nasal cavities.
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