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Introduction

Clinical picture and impact of flu

Transmission and pathogenesis

After being inhaled by aerosol or droplet transmission, the influenza virus attacks the respiratory epithelium and commandeers the host cell's replication machinery to produce new progeny virus particles, which further infect other cells (see Chapters 2 and 5). “Innate” immune responses retard the initial spread of the virus in the respiratory tract and provide valuable time for the host to mount a specific “adaptive” immune response against the invading virus. B-lymphocytes produce antibodies that bind to and neutralize the virus on the mucosal surfaces, while T-lymphocytes dispose of the infected cells that have become factories for producing new virus particles (see Chapter 4).

The body's immune response to influenza produces a number of inflammatory cytokines, which are responsible for most of the symptoms of influenza. Except in rare circumstances, the virus remains limited to the respiratory epithelium (see Chapter 2). Thus, the major systemic symptoms such as fever, myalgia and malaise are caused by these circulating cytokines. Influenza is generally a self-limiting disease. However, in the complete absence of immunity to a specific subtype of influenza, such as with the emergence of a novel pandemic strain, even young people may die within 24–48 hours of the onset of symptoms, the overwhelming inflammatory response to the virus causing an acute respiratory distress-like syndrome. Inadequate immune responses as often occur in the very young and very old may lead to a primary viral pneumonia or secondary bacterial infection (see Chapter 5).

Impact of influenza epidemics and pandemics

Influenza epidemics have been recognized as a major cause of morbidity and increased mortality, especially in the very young, the very old, people with chronic cardiopulmonary conditions, pregnant women and immunocompromised individuals (see Chapter 6). Each year, influenza results in 3–5 million cases of severe illness and kills between 0.25 and 0.5 million people worldwide. 7, x KG Nicholson, JM Wood, M Zambon. Influenza. Lancet 362 (2003) (1733 - 1745) Crossref. 29 x Influenza: Report by the WHO Secretariat for 111th session of the WHO Executive Board, January 2003. Document EB111/10 (WHO, November 2002) (www.who.int/gb/ebwha/pdf_files/EB111/eeb11110.pdf) The WHO estimates that there are currently 1 billion people worldwide who are at high risk of suffering or dying from influenza and its complications. 29 x Influenza: Report by the WHO Secretariat for 111th session of the WHO Executive Board, January 2003. Document EB111/10 (WHO, November 2002) (www.who.int/gb/ebwha/pdf_files/EB111/eeb11110.pdf) Furthermore, as the elderly population increases, future influenza epidemics will be associated with ever-increasing hospitalization rates and excess mortality unless adequate prophylactic measures are taken. In developed countries, about 100 people per million population die annually from influenza. 7, x KG Nicholson, JM Wood, M Zambon. Influenza. Lancet 362 (2003) (1733 - 1745) Crossref. 30 x WH Barker, JP Mullooly. Impact of epidemic type A influenza in a defined adult population. Am J Epidemiol 112 (1980) (798 - 811) Most of these deaths (95%) occur in those over 60 years of age (12%, 29% and 54% in people aged 60–69, 70–79 and >80 years respectively). 31 x MJ Sprenger, PG Mulder, WE Beyer, et al.. Impact of influenza on mortality in relation to age and underlying disease, 1967–1989. Int J Epidemiol 22 (1993) (334 - 340)

As indicated above, the three major pandemic outbreaks of influenza in the 20th century have caused many millions of deaths, and future pandemics are also expected to have a devastating impact on society. 32 x MI Meltzer, NJ Cox, K Fukuda. The economic impact of pandemic influenza in the United States: priorities for intervention. Emerg Infect Dis 5 (1999) (659 - 671) Crossref. Yet, it has been estimated that the cumulative mortality of annual influenza epidemics in the last century exceeded that of the three major pandemic outbreaks. 7, x KG Nicholson, JM Wood, M Zambon. Influenza. Lancet 362 (2003) (1733 - 1745) Crossref. 33 x L Simonson, MJ Clarke, GD Williamson, et al.. The impact of influenza epidemics on mortality: introducing a severity index. Am J Public Health 87 (1997) (1944 - 1950) This underscores the fact that not only influenza pandemics but also the recurrent annual outbreaks of flu remain a major health threat worldwide. Thus, public-health policy needs to address the interrelated issues of optimizing both the effectiveness of annual vaccination programmes and the preparedness for future pandemic outbreaks of influenza. Health-care professionals play a key role in this regard by participating in influenza surveillance and by providing appropriate preventive and treatment regimens for their patients.

References

Label Authors Title Source Year
7

References in context

  • The burden of influenza for the society, not only from a clinical but also from an economic perspective, is often underestimated.7 This relates particularly to the recurring annual winter epidemics.
    Go to context

  • Each year, influenza results in 3–5 million cases of severe illness and kills between 0.25 and 0.5 million people worldwide.7,29 The WHO estimates that there are currently 1 billion people worldwide who are at high risk of suffering or dying from influenza and its complications.29 Furthermore, as the elderly population increases, future influenza epidemics will be associated with ever-increasing hospitalization rates and excess mortality unless adequate prophylactic measures are taken.
    Go to context

  • Each year, influenza results in 3–5 million cases of severe illness and kills between 0.25 and 0.5 million people worldwide.7,29 The WHO estimates that there are currently 1 billion people worldwide who are at high risk of suffering or dying from influenza and its complications.29 Furthermore, as the elderly population increases, future influenza epidemics will be associated with ever-increasing hospitalization rates and excess mortality unless adequate prophylactic measures are taken.
    Go to context

  • As indicated above, the three major pandemic outbreaks of influenza in the 20th century have caused many millions of deaths, and future pandemics are also expected to have a devastating impact on society.32 Yet, it has been estimated that the cumulative mortality of annual influenza epidemics in the last century exceeded that of the three major pandemic outbreaks.7,33 This underscores the fact that not only influenza pandemics but also the recurrent annual outbreaks of flu remain a major health threat worldwide.
    Go to context

KG Nicholson, JM Wood, M Zambon. Influenza. Crossref. Lancet 362 (2003) (1733 - 1745) 2003
29

References in context

  • Each year, influenza results in 3–5 million cases of severe illness and kills between 0.25 and 0.5 million people worldwide.7,29 The WHO estimates that there are currently 1 billion people worldwide who are at high risk of suffering or dying from influenza and its complications.29 Furthermore, as the elderly population increases, future influenza epidemics will be associated with ever-increasing hospitalization rates and excess mortality unless adequate prophylactic measures are taken.
    Go to context

  • Each year, influenza results in 3–5 million cases of severe illness and kills between 0.25 and 0.5 million people worldwide.7,29 The WHO estimates that there are currently 1 billion people worldwide who are at high risk of suffering or dying from influenza and its complications.29 Furthermore, as the elderly population increases, future influenza epidemics will be associated with ever-increasing hospitalization rates and excess mortality unless adequate prophylactic measures are taken.
    Go to context

  • However, despite the established effectiveness of immunization, the national and international response to influenza prevention measures is often inadequate (see Chapter 8).
    Go to context

  • However, despite the established effectiveness of immunization, the national and international response to influenza prevention measures is often inadequate (see Chapter 8).
    Go to context

  • In 2003, a resolution of the World Health Assembly urged member states to increase their efforts in the area of influenza prevention.29 In November 2005, during a large international meeting with participation of the WHO, the World Bank, the UN co-ordinator for pandemic preparedness and delegates from over 100 countries,35 there was broad consensus that the threat of a pandemic remains.
    Go to context

Influenza: Report by the WHO Secretariat for 111th session of the WHO Executive Board, January 2003. Document EB111/10 (WHO, November 2002) (www.who.int/gb/ebwha/pdf_files/EB111/eeb11110.pdf) November 2002
30

References in context

  • Influenza epidemics have been recognized as a major cause of morbidity and increased mortality, especially in the very young, the very old, people with chronic cardiopulmonary conditions, pregnant women and immunocompromised individuals (see Chapter 6).
    Go to context

WH Barker, JP Mullooly. Impact of epidemic type A influenza in a defined adult population. Am J Epidemiol 112 (1980) (798 - 811) 1980
31

References in context

  • Influenza epidemics have been recognized as a major cause of morbidity and increased mortality, especially in the very young, the very old, people with chronic cardiopulmonary conditions, pregnant women and immunocompromised individuals (see Chapter 6).
    Go to context

MJ Sprenger, PG Mulder, WE Beyer, et al.. Impact of influenza on mortality in relation to age and underlying disease, 1967–1989. Int J Epidemiol 22 (1993) (334 - 340) 1993
32

References in context

  • As indicated above, the three major pandemic outbreaks of influenza in the 20th century have caused many millions of deaths, and future pandemics are also expected to have a devastating impact on society.32 Yet, it has been estimated that the cumulative mortality of annual influenza epidemics in the last century exceeded that of the three major pandemic outbreaks.7,33 This underscores the fact that not only influenza pandemics but also the recurrent annual outbreaks of flu remain a major health threat worldwide.
    Go to context

MI Meltzer, NJ Cox, K Fukuda. The economic impact of pandemic influenza in the United States: priorities for intervention. Crossref. Emerg Infect Dis 5 (1999) (659 - 671) 1999
33

References in context

  • As indicated above, the three major pandemic outbreaks of influenza in the 20th century have caused many millions of deaths, and future pandemics are also expected to have a devastating impact on society.32 Yet, it has been estimated that the cumulative mortality of annual influenza epidemics in the last century exceeded that of the three major pandemic outbreaks.7,33 This underscores the fact that not only influenza pandemics but also the recurrent annual outbreaks of flu remain a major health threat worldwide.
    Go to context

L Simonson, MJ Clarke, GD Williamson, et al.. The impact of influenza epidemics on mortality: introducing a severity index. Am J Public Health 87 (1997) (1944 - 1950) 1997

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