Influenza, commonly called the “flu”, is a viral infectious disease, which primarily affects the major structures of the upper, as well as the lower respiratory tract. It causes the inflammation of throat (pharyngitis), voice box (laryngitis), nose (rhinitis), sinus cavities (sinusitis) and in some cases even bronchi (bronchitis) and bronchioles and alveoli (pneumonia). There is an increased incidence of flu during winter and early spring months. Seasonality depends on both environmental factors (causative agents occur more often during winter, low temperature induces changes in the respiratory system, low humidity increases viral transmission rates) and social factors (people spending more time indoors, beginning of the school year, insufficient room ventilation). Although it is typically a mild and self-limiting illness (approximately 33% of people with the flu do not experience any visible symptoms), it can be dangerous, even life-threatening for high risk populations such as infants, young children, the elderly, pregnant women and immunocompromised and chronic patients.
Flu epidemics occur annually worldwide, due to the high contagiousness and mutation rate of the influenza viruses, which represents a serious public health problem. This is why it is very important to educate people about prevention measures and the disease itself, as well as how to recognize the symptoms and start the treatment on time. Larger outbreaks called pandemics, on the other hand, are less frequent (they occur about three times per century), but far more severe. They infect much larger proportion of the world’s population and potentially can kill tens of millions of people. The last one, caused by a new strain of influenza A(H1N1), also known as the “swine flu”, occurred in June 2009 and killed more than 300,000 people.
Flu symptoms typically occur after the incubation period of just 2-3 days. Majority of people develop the so called “uncomplicated influenza” with milder and non-specific symptoms, such as runny nose, nasal congestion, sore throat, cough, sneezing, muscle ache, fatigue and headache. These symptoms are very similar to those of common cold and other URTI, which makes it difficult to distinguish between mentioned conditions in the early stages of infection. However, as the flu progresses, infected person develops high fever (body temperature up to 39°C), feeling of coldness with chills, extreme fatigue and worsened muscle and joint pains, along with severe headache. Children can develop gastrointestinal symptoms, such as diarrhea and abdominal pain. Most of the symptoms usually last from 7 to 10 days in adults, except cough, that can last up to 3 weeks. Young children, pregnant women, older people and chronic patients, on the other hand, can develop “complicated influenza”, which is followed by symptoms of lower respiratory tract infection, such as hypoxaemia, dyspnea or lung infiltrate and requires hospital admission.
Flu is a viral disease, which is caused by three different types of influenza viruses in humans – influenza A, influenza B and influenza C virus.
Influenza A viruses are characterized by high contagiousness and high mutation rate, compared to other two types. They cause seasonal flu epidemics every year worldwide and are responsible for the most severe cases of the disease. Influenza A viruses can be subdivided into different serotypes, based on two proteins on the surface of the virus, called the hemagglutinin (HA) and the neuraminidase (NA). The fact that there are 18 different hemagglutinin subtypes (H1-H18) and 11 different neuraminidase subtypes (N1-N11) indicates high genetic diversity within the type A group. Two subtypes currently circulating in human population are influenza A(H1N1) and A(N3N2), along with several influenza B viruses, that are all included in each year’s influenza vaccine. Influenza pandemics occur every 30 to 40 years and they were all caused by type A viruses. The last one, that occurred in June 2009, was caused by a new strain of influenza A(H1N1), also known as the “swine flu”. It is estimated that more than 300,000 people have died as a result of this pandemic.
Influenza B viruses are less virulent than the type A viruses and consequently do not cause pandemics. Still, they are affecting humans on a certain level, which is why they are included in seasonal flu vaccine.
Influenza C virus is less common than the other two types and it is known to cause only mild illness in children.
Flu can be transmitted very easily via direct person-to-person contact, by inhaling aerosols of respiratory droplets that contain the virus. Other methods of transmission include touching the contaminated surfaces (hand-to-surface contact) or touching the nose or mouth by hand, which are the two main portals of entry for infectious pathogens into the body. Transmission is very often in nurseries, schools, public transportation, as well as all places that include people sitting in close proximity to one another.
In most cases of uncomplicated influenza treatment is typically symptomatic. It includes over-the-counter (OTC) drugs and various dietary supplements, which alleviate the symptoms, such as headache, muscle ache, nasal congestion, sore throat, and cough. Most commonly used OTC drugs are analgesics (relieve pain caused by muscle ache or a headache), antipyretics (lower the body temperature in febrile patients), nasal decongestants (relieve nasal congestion) and cough medicines (suppress a dry cough, improve chesty cough). Dietary supplements in the form of oriblettes, pastilles or lozenges, which contain antiseptic and anti-inflammatory substances, such as sage essential oil and bee propolis, are often used for treating sore throat and hoarseness. Vitamin C dietary supplements may shorten the duration of illness, when taken on a regular basis. It is also recommended to get plenty of rest, drink enough liquids to avoid dehydration and avoid smoking and drinking alcohol.
Antibiotics, on the other hand, have no effect against viral infections and should not be used for treating the flu. Although doctors have been strongly encouraged to decrease the antibiotic usage in the treatment of influenza, unfortunately, they are still frequently prescribed (according to several studies in more than 50% of all cases). This represents the world-wide problem, because it leads to the creation of antibiotic-resistant strains of bacteria. In the past twenty years there has been a significant increase in antibiotic resistance rates in the human population. Antibiotics use is, however, justified for treating possible bacterial complications (secondary infections) of the flu, such as bacterial sinusitis and bacterial pneumonia.
Antiviral medication, which represents a specifically targeted therapy is also available. However, there are concerns about its effectiveness, due to the resistance of some strains of influenza to the standard antiviral drugs. The most commonly used antivirals are the neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir. They can shorten the duration of symptoms by approximately one day and reduce the potential for developing serious complications, especially in high-risk populations, such as pregnant women, people older than 65 years or chronic patients. Some evidence indicates that their benefits in otherwise healthy adults do not appear to be greater than their risks.
Flu is a highly contagious and widespread disease, but it can be prevented on a certain level by following several important guidelines:
- avoid direct contact with another infected person for the first 2-3 days of their illness
- wash hands thoroughly on a regular basis (especially important for children)
- avoid touching the mouth or nose (common portals of entry for the virus)
- wear a surgical mask when being near to the infected person
- wear a surgical mask if you are infected, to avoid passing the virus to other people
- avoid crowded areas during the flu season
- do not share drinks or food with other people
However, the most effective method of prevention remains yearly vaccination against influenza. It is recommended by the World Health Organization for the following high-risk groups:
- pregnant women at any stage of pregnancy
- children aged 6 months to 5 years
- elderly individuals (≥65 years of age)
- chronic patients
- immunocompromised patients
- health-care workers
The seasonal flu vaccine has to be reformulated annually, due to the high mutation rate of influenza viruses. The World Health Organization predicts which strains of the virus are most likely to be circulating during the upcoming season. Most common flu vaccines are called the trivalent vaccines, since they protect against three subtypes of flu viruses – influenza A (H1N1), influenza A (H3N2) and influenza B virus. Quadrivalent vaccines, which protect against additional influenza B virus are also available. It is recommended to get vaccinated early in the fall, before the flu season starts, while it takes about two weeks for the antibodies to develop in the body and provide protection after vaccination.
by: mr ph Iva Majstorović, posted on March 22, 2015
1. Influenza (Seasonal). WHO
2. Key Facts about Influenza (Flu) & Flu Vaccine.
3. Centers for Disease Control and Prevention. Flu Symptoms and Severity.
4. Understanding the symptoms of the common cold and influenza. The Lancet. Infectious Diseases.
5. Centers for Disease Control and Prevention. Types of Influenza viruses.
6. Treating flu. NHS Choices.
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