Influenza is a contagious disease caused by influenza viruses, typically occurring during the period from autumn to early spring.

Influenza viruses are divided into four types: A, B, C, and D. The main source of the Influenza A virus, which is most commonly found in mammals, particularly humans and pigs, is birds. Influenza B and C viruses primarily cause disease in humans. The Influenza D virus is found mainly in cattle and pigs, and it is not fully known whether it causes disease in humans.

The influenza virus is an enveloped RNA virus. Among this group, the Influenza A virus is the virus that causes epidemics and even pandemics. Influenza A is recognized by the variations in the H (hemagglutinin) and N (neuraminidase) proteins found in its envelope structure and is named accordingly. For example, the type known as H1N1 caused the pandemic known as the Spanish Flu Pandemic between 1918 and 1920, during which 50 million people lost their lives according to official records. This was followed by the pandemics of 1957-1958 (H2N2), 1968-1969 (H3N2), and 1977-1978 (H1N1). Today, the H3N1 and H1N1 viruses circulate together worldwide. Avian influenza, also known as bird flu, is a disease caused by influenza A viruses. The H5N1 strain of this virus can infect humans and cause illness. The disease is transmitted through contact with the saliva and feces of migratory birds.

Transmission

The virus spreads to healthy individuals through droplets released into the environment when infected individuals cough, sneeze, or talk, and it settles in the respiratory tract, where it begins to multiply. It is transmitted through inhalation. When an infected person coughs or sneezes, millions of droplets containing the virus are dispersed. These droplets have been shown to spread up to approximately 1-2 meters.

To a lesser extent, the disease can also be transmitted by touching surfaces and objects contaminated with these droplets and then touching the mouth, nose, or eyes. Shaking hands, kissing, and talking within one meter of each other are significant routes of transmission. The virus can remain viable on surfaces such as door handles, tables, and cups for 2-8 hours. Sick individuals are contagious from 1 day before the onset of symptoms until the 5th-7th day of the illness.

Symptoms

Flu symptoms appear within 1-3 days after the virus enters the body and include the following:

  • Fever (38 °C or higher when measured under the armpit)
  • Chills
  • Dry cough
  • Sore throat
  • Runny nose and congestion
  • Headache
  • Muscle and joint pain
  • Severe fatigue
  • Diarrhea, rarely vomiting

In individuals in the risk group in particular, the disease can progress to pneumonia due to lung involvement. During the course of the disease, secondary bacterial lung infections may occur in individuals in the risk group due to a decrease in the immune response, and individuals who contract the disease may lose their lives due to these severe disease conditions.

Diagnosis

Although clinical findings often suggest the diagnosis, a definitive diagnosis can be made by polymerase chain reaction (PCR) testing of a throat swab sample to detect the virus's genetic material.

Treatment

Since influenza is a viral infection, antibiotics used against bacteria are ineffective. Antiviral drugs are currently available to treat the disease, but they must be started early in the course of the illness. In addition, in healthy young individuals with a good immune response, the disease resolves spontaneously within about a week. For these individuals, taking paracetamol for fever and muscle and joint pain, drinking plenty of fluids, and resting in bed are sufficient to overcome the disease.

In individuals at risk, if the disease is severe or involves the lungs, treatment should be carried out in a hospital.

Prevention

Since the virus is transmitted through droplets, close contact with sick people and sharing items (such as towels) with them should be avoided. Individuals who are sick should separate their belongings to avoid infecting others and should not go outside unless absolutely necessary. Wearing a mask is an important method to prevent the spread of the disease.

The most important method to protect individuals in the risk group against the disease is to get a flu shot every year in the fall. The individuals in the risk group who should get the vaccine are listed below.

  • People aged 65 and over
  • People with chronic illnesses: those with chronic heart, lung, liver, kidney, diabetes, and similar diseases.
  • People with weakened immune systems: cancer patients, people with immune system disorders, people who have undergone organ and bone marrow transplants
  • Children and young people receiving long-term aspirin treatment
  • Doctors, nurses, and caregivers working in hospitals; daycare and nursing home staff
  • Individuals in close contact with high-risk individuals
  • Pregnant women after the first three months
  • Infants from six months of age
  • If people around you have the flu, getting a flu shot is strongly recommended.