Flu season
Encyclopedia
Flu season is a annually-recurring time period characterized by the prevalence of outbreaks of influenza
(flu). The season occurs during the cold half of the year in each hemisphere
. Influenza activity can sometimes be predicted and even tracked geographically. While the beginning of major flu activity in each season varies by location, in any specific location these minor epidemics usually take about 3 weeks to peak and another 3 weeks to significantly diminish.
families, Influenzavirus A
, B
, and C
are the main infective agents that cause influenza. During periods of cooler temperature, influenza cases increase roughly tenfold or more. Despite higher incidence of manifestations of the flu during the season, the viruses are actually transmitted throughout populations all year round.
Each annual flu season is normally associated with a major influenzavirus subtype. The associated subtype changes each year, due to development of immunological resistance to a previous year's strain (through exposure and vaccinations), and mutational changes in previously dormant viruses strains.
Research in guinea pigs has shown that the aerosol
transmission of the virus is enhanced when the air is cold and dry. The dependence on aridity appears to be due to degradation of the virus particles in moist air, while the dependence on cold appears to be due to infected hosts shedding the virus for a longer period of time. The researchers did not find that the cold impaired the immune response of the guinea pigs to the virus.
Recent research done by National Institute of Child Health and Human Development (NICHD) found that the influenza virus has a "butter-like coating". The coating melts when it enters the respiratory tract. In the winter, the coating becomes a hardened shell; therefore, it can survive in the cold weather similar to a spore. In the summer, the coating melts before the virus reaches the respiratory tract.
and Southern Hemisphere
have winter at different times of the year, there are actually two flu seasons each year. Therefore, the World Health Organization
(assisted by the National Influenza Centers
) makes two vaccine
formulations every year; one for the Northern, and one for the Southern Hemisphere.
According to the U.S. Department of Health, a growing number of large companies provide their employees with seasonal flu shots, either at a small cost to the employee or as a free service.
The annually updated trivalent influenza vaccine consists of hemagglutinin
(HA) surface glycoprotein components from influenza H3N2
, H1N1
, and B influenza
viruses. The dominant strain in January 2006 was H3N2. Measured resistance to the standard antiviral drugs amantadine
and rimantadine
in H3N2 has increased from 1% in 1994 to 12% in 2003 to 91% in 2005.
. When blood sugar
s are not well controlled, diabetics can quickly develop a wide range of complications. Diabetes results in elevated blood sugars in the body, and this environment allows viruses and bacteria
to thrive.
If blood sugars are poorly controlled, a mild flu can quickly turn severe, leading to hospitalization and even death
. Uncontrolled blood sugars suppresses the immune system
s and generally lead to more severe cases of the common cold
or influenza. Thus it has been recommended that diabetics are vaccinated against flu, before the start of the flu season.
tics be vaccinated against flu before the flu season. People with asthma can develop life-threatening complications from influenza and the common cold virus. Some of these complications include pneumonia
s and acute respiratory distress syndrome
.
Each year flu related complications in the USA affect close to 100,000 asthmatics, and millions more are seen in the emergency room
because of severe shortness of breath. It is recommended that asthmatics are vaccinated between October and November, before the peak of the flu season. Flu vaccine works by boosting the body's immune system and takes about 2 weeks to become effective.
usually have a suppressed immune system
. Moreover, many cancer patients undergo radiation therapy
and potent immunosuppressive medications, which further suppresses the body's ability to fight off infections. Everyone with cancer is highly susceptible and is at risk for complications from flu. It is recommended that all patients who have or have had cancer receive the H1N1 and common cold vaccine, and take medical advice if they contract a common cold or flu.
) are very prone to a variety of infections. HIV has a tremendous capacity to destroy the body's immune system and this makes one prone to not only viral infections but also bacterial fungal and protozoa
disorders. People with HIV are at an increased risk of serious flu-related complications. Many reports have shown that individuals with HIV can develop serious pneumonias which need hospitalization and aggressive antibiotic
therapy. Moreover people with HIV have a longer flu season and are at a high risk of death. Vaccination with the flu shot has been shown to boost the immune system and protect against the seasonal flu in some patients with HIV; individuals who have HIV should only get vaccinated with the inactivated influenza vaccine. Any HIV patient who has been exposed to other people with influenza should see a physician to determine if there is a need for anti viral medications
.
A recent study estimated that in the United States
, annual influenza epidemics result in approximately 600,000 life-years lost, 3 million hospitalized days, and 30 million outpatient visits, resulting in medical costs of $10 billion annually. According to this study, lost earnings due to illness and loss of life amounted to over $15 billion annually and the total economic burden of annual influenza epidemics amounts to over $80 billion. Also, in the US the flu season usually accounts for 200,000 hospitalizations and 41,000 deaths. Because the mortality rate of the H1N1 "swine flu" is lower than common flu strains, this number was actually lower in 2009.
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
(flu). The season occurs during the cold half of the year in each hemisphere
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Influenza activity can sometimes be predicted and even tracked geographically. While the beginning of major flu activity in each season varies by location, in any specific location these minor epidemics usually take about 3 weeks to peak and another 3 weeks to significantly diminish.
Cause
Three virusVirus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
families, Influenzavirus A
Influenzavirus A
Influenza A virus causes influenza in birds and some mammals and is the only species of Influenzavirus A. Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon...
, B
Influenzavirus B
Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called "Influenza B virus".Influenza B viruses are only known to infect humans and seals, giving them influenza...
, and C
Influenzavirus C
Influenzavirus C is a genus in the virus family Orthomyxoviridae, which includes those viruses which cause influenza. The only species in this genus is called "Influenza C virus".Influenza C viruses are known to infect humans and pigs, giving them influenza...
are the main infective agents that cause influenza. During periods of cooler temperature, influenza cases increase roughly tenfold or more. Despite higher incidence of manifestations of the flu during the season, the viruses are actually transmitted throughout populations all year round.
Each annual flu season is normally associated with a major influenzavirus subtype. The associated subtype changes each year, due to development of immunological resistance to a previous year's strain (through exposure and vaccinations), and mutational changes in previously dormant viruses strains.
Mechanism for seasonal nature of influenza
The exact mechanism behind the seasonal nature of influenza outbreaks is unclear. Some proposed explanations are:- People are indoors more often during the winter, they are in close contact more often, and this promotes transmission from person to person.
- Cold temperatures lead to drier air, which may dehydrate mucus membranes, preventing the body from effectively defending against respiratory virus infections. PMID 19204283
- The virus may linger longer on exposed surfaces (doorknobs, countertops, etc.) in colder temperatures.
- In nations where children do not go to school in the summer, there is a more pronounced beginning to flu season, coinciding with the start of public school. It is thought that the crecheCrècheCrèche may refer to:*Day care center, an organization of adults who take care of children in place of their parents*Nativity scene, a group of figures arranged to represent the birth of Jesus Christ...
environment is perfect for the spread of illness. - Vitamin DVitamin DVitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
production from Ultraviolet-B in the skin changes with the seasons and affects the immune system.
Research in guinea pigs has shown that the aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
transmission of the virus is enhanced when the air is cold and dry. The dependence on aridity appears to be due to degradation of the virus particles in moist air, while the dependence on cold appears to be due to infected hosts shedding the virus for a longer period of time. The researchers did not find that the cold impaired the immune response of the guinea pigs to the virus.
Recent research done by National Institute of Child Health and Human Development (NICHD) found that the influenza virus has a "butter-like coating". The coating melts when it enters the respiratory tract. In the winter, the coating becomes a hardened shell; therefore, it can survive in the cold weather similar to a spore. In the summer, the coating melts before the virus reaches the respiratory tract.
Flu vaccinations
Flu vaccinations have been used to diminish the effects of the flu season. Since the NorthernNorthern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
and Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
have winter at different times of the year, there are actually two flu seasons each year. Therefore, the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
(assisted by the National Influenza Centers
National Influenza Centers
National Influenza Centers are institutions which are formally recognized as such by the World Health Organization ."The WHO Global Influenza Surveillance Network was established in 1952...
) makes two vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
formulations every year; one for the Northern, and one for the Southern Hemisphere.
According to the U.S. Department of Health, a growing number of large companies provide their employees with seasonal flu shots, either at a small cost to the employee or as a free service.
The annually updated trivalent influenza vaccine consists of hemagglutinin
Hemagglutinin
Influenza hemagglutinin or haemagglutinin is a type of hemagglutinin found on the surface of the influenza viruses. It is an antigenic glycoprotein. It is responsible for binding the virus to the cell that is being infected...
(HA) surface glycoprotein components from influenza H3N2
H3N2
Influenza A virus subtype H3N2 is a subtype of viruses that cause influenza . H3N2 Viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains...
, H1N1
H1N1
'Influenza A virus is a subtype of influenza A virus and was the most common cause of human influenza in 2009. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza. H1N1 strains caused a few percent of...
, and B influenza
Influenzavirus B
Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called "Influenza B virus".Influenza B viruses are only known to infect humans and seals, giving them influenza...
viruses. The dominant strain in January 2006 was H3N2. Measured resistance to the standard antiviral drugs amantadine
Amantadine
Amantadine is the organic compound known formally as 1-adamantylamine or 1-aminoadamantane. The molecule consists of adamantane backbone that has an amino group substituted at one of the four methyne positions. This pharmaceutical is sold under the name Symmetrel for use both as an antiviral and an...
and rimantadine
Rimantadine
Rimantadine is an orally administered antiviral drug used to treat, and in rare cases prevent, influenzavirus A infection. When taken within one to two days of developing symptoms, rimantadine can shorten the duration and moderate the severity of influenza. Both rimantadine and the similar drug...
in H3N2 has increased from 1% in 1994 to 12% in 2003 to 91% in 2005.
Health conditions likely to cause complications
Medical conditions that compromise the immune system increase the risks from flu.Diabetes
Millions of people have diabetesDiabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
. When blood sugar
Blood sugar
The blood sugar concentration or blood glucose level is the amount of glucose present in the blood of a human or animal. Normally in mammals, the body maintains the blood glucose level at a reference range between about 3.6 and 5.8 mM , or 64.8 and 104.4 mg/dL...
s are not well controlled, diabetics can quickly develop a wide range of complications. Diabetes results in elevated blood sugars in the body, and this environment allows viruses and bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
to thrive.
If blood sugars are poorly controlled, a mild flu can quickly turn severe, leading to hospitalization and even death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
. Uncontrolled blood sugars suppresses the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
s and generally lead to more severe cases of the common cold
Common cold
The common cold is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever...
or influenza. Thus it has been recommended that diabetics are vaccinated against flu, before the start of the flu season.
Asthma
It is recommended that asthmaAsthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
tics be vaccinated against flu before the flu season. People with asthma can develop life-threatening complications from influenza and the common cold virus. Some of these complications include pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
s and acute respiratory distress syndrome
Acute respiratory distress syndrome
Acute respiratory distress syndrome , also known as respiratory distress syndrome or adult respiratory distress syndrome is a serious reaction to various forms of injuries to the lung....
.
Each year flu related complications in the USA affect close to 100,000 asthmatics, and millions more are seen in the emergency room
Emergency department
An emergency department , also known as accident & emergency , emergency room , emergency ward , or casualty department is a medical treatment facility specialising in acute care of patients who present without prior appointment, either by their own means or by ambulance...
because of severe shortness of breath. It is recommended that asthmatics are vaccinated between October and November, before the peak of the flu season. Flu vaccine works by boosting the body's immune system and takes about 2 weeks to become effective.
Cancer
People with cancerCancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
usually have a suppressed immune system
Immunosuppression
Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immuno-suppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other...
. Moreover, many cancer patients undergo radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
and potent immunosuppressive medications, which further suppresses the body's ability to fight off infections. Everyone with cancer is highly susceptible and is at risk for complications from flu. It is recommended that all patients who have or have had cancer receive the H1N1 and common cold vaccine, and take medical advice if they contract a common cold or flu.
HIV/AIDS
Individuals who acquire the human immune deficiency virus (HIVHIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
) are very prone to a variety of infections. HIV has a tremendous capacity to destroy the body's immune system and this makes one prone to not only viral infections but also bacterial fungal and protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
disorders. People with HIV are at an increased risk of serious flu-related complications. Many reports have shown that individuals with HIV can develop serious pneumonias which need hospitalization and aggressive antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
therapy. Moreover people with HIV have a longer flu season and are at a high risk of death. Vaccination with the flu shot has been shown to boost the immune system and protect against the seasonal flu in some patients with HIV; individuals who have HIV should only get vaccinated with the inactivated influenza vaccine. Any HIV patient who has been exposed to other people with influenza should see a physician to determine if there is a need for anti viral medications
Antiviral drug
Antiviral drugs are a class of medication used specifically for treating viral infections. Like antibiotics for bacteria, specific antivirals are used for specific viruses...
.
Cost
The cost of a flu season in lives lost, medical expenses and economic impact can be severe.- "In the United States of America, for example, recent estimates put the cost of influenza epidemics to the economy at US$ 71-167 billion per year."
A recent study estimated that in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, annual influenza epidemics result in approximately 600,000 life-years lost, 3 million hospitalized days, and 30 million outpatient visits, resulting in medical costs of $10 billion annually. According to this study, lost earnings due to illness and loss of life amounted to over $15 billion annually and the total economic burden of annual influenza epidemics amounts to over $80 billion. Also, in the US the flu season usually accounts for 200,000 hospitalizations and 41,000 deaths. Because the mortality rate of the H1N1 "swine flu" is lower than common flu strains, this number was actually lower in 2009.
See also
- InfluenzaInfluenzaInfluenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
- Influenza vaccine
- Bird flu
- Human fluHuman fluHuman flu is a term used to refer to influenza cases caused by Orthomyxoviridae that are endemic to human populations . It is an arbitrary categorization scheme, and is not associated with phylogenetics-based taxonomy...
- Swine flu
- Horse flu
- Dog fluCanine influenzaCanine influenza is influenza occurring in canines. Canine influenza is caused by varieties of Influenzavirus A, such as equine influenza virus H3N8, which in 2004 was discovered to cause disease in dogs. Because of the lack of previous exposure to this virus, dogs have no natural immunity to...
- Freshers' fluFreshers' FluFreshers' Flu is the name commonly given to a battery of illnesses contracted by as many as 90% of new students during the first few weeks at a university, in some form; common symptoms include fever, sore throat, severe headache, coughing and general discomfort...
External links
- Health-EU portal EU response to influenza
- European Commission - Public Health EU coordination on Pandemic (H1N1) 2009
Further reading
- CDC U.S. influenza season summary with weekly updates — Contains about a dozen charts and graphs with extensive text