Seasonal influenza is an acute respiratory illness caused by influenza viruses that typically occurs during winter. Common signs include fever, cough, sore throat, and muscle aches. While influenza is usually self-limiting, it can lead to serious complications like pneumonia, especially in high-risk groups. Pneumonia is the most common complication and can be either viral or secondary bacterial infections with pathogens like streptococcus pneumoniae or staphylococcus aureus. Influenza may also cause other rare complications affecting the heart, brain or muscles.

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Seasonal Influenza , or ‘the flu’ as it is often called, is an
acute respiratory illness caused by influenza A or B
viruses that occurs in outbreaks and epidemics
worldwide, mainly during the winter season.

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 The clinical presentation of influenza can vary from
asymptomatic infection or a self-limiting upper respiratory
tract infection to a severe illness, often with serious,
potentially fatal complications.
 The clinical course is dependent on the virulence of the
virus , the age of the patient , and the presence of chronic
medical illness, such as cardiac and pulmonary diseases,
immunosuppression and pregnancy enhance the severity
of illness.

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Common signs and symptoms of the flu include:
 Fever over 100.4 F (38 C)
 Aching muscles, especially in your back, arms and legs.
 Chills and sweats.
 Headache.
 Dry, persistent cough.
 Fatigue and weakness.
 Nasal congestion.
 Sore throat.

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Typical influenza disease does not occur in every infected
person, In otherwise healthy individuals, influenza infection
normally results in an uncomplicated URTI that resolves
within 1–2 weeks.
In most cases, illness resolves within 3 to 7 days, although
cough and malaise can persist for more than 2 weeks.

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Influenza is a self-limited infection in the general population
(uncomplicated influenza); however, it is associated with
increased morbidity and mortality in certain high-risk
populations .
influenza can be severe and lead to hospitalization and even
death (complicated influenza).

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Pulmonary Complications of influenza
 The most frequent complication of influenza is pneumonia,
with secondary bacterial pneumonia being the most
common form, and primary viral influenza pneumonia the
most severe.
 Combined viral–bacterial pneumonia is more common than
primary viral pneumonia and frequently occurs during
outbreaks. .

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 The Secondary bacterial pneumonia is most commonly
caused by Streptococcus pneumoniae, Staphylococcus
aureus, and Haemophilus influenzae.
 Typically, patients may initially recover from the acute
influenza illness over 2 to 3 days before having rising
temperatures again.
Secondary Bacterial Pneumonia

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Secondary Bacterial Pneumonia
 Clinical signs and symptoms are consistent with classical
bacterial pneumonia: cough, purulent sputum, and physical
and x-ray signs of consolidation.
 Gram staining and culture of sputum specimens may
determine the aetiology.
 Chronic cardiac and pulmonary disease predispose to
secondary bacterial pneumonia, as does older age.

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Secondary Bacterial Pneumonia
 Bacterial pneumonia as a complication of influenza has
a different presentation from primary viral pneumonia ,Patients
initially show clinical improvement from illness and then
develop worsening respiratory symptoms.
 In this case, physical and chest X-ray examinations are more
likely to show localized signs of consolidation.
 Of patients with a severe pneumonia, 75% will have secondary
bacterial infection.

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Primary viral Pneumonia
 In primary viral pneumonia, typical influenza is followed by a
rapid progression (over 2–3 days) of fever, cough, dyspnoea,
chest pain and cyanosis.
 Physical examination & chest X-ray disclose diffuse bilateral
infiltrates consistent with acute respiratory distress
syndrome. If fatal, death usually occurs within 4–5 days of
first symptoms.

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Other Complications of influenza
 Influenza infection has also been associated with :
Encephalopathy
Transverse myelitis
Myositis
Myocarditis
Pericarditis
Reye's syndrome.
 Influenza may exacerbate heart or lung diseases or other
chronic conditions.

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 Fever
 Cough
 Sore throat
 Muscle pain
 Malaise
 No dyspnea and
shortness of breath
 GIT symptom may also
present
 Shortness of breath and
dyspnea
 Lower RTI ( pneumonia )
 CNS involvement
 Severe dehydration
 Secondary complications
 COPD – asthma
exacerbation
•
Complicated
influenza
•
Uncomplicated
influenza

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Influenza not just as a common cold

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