GP - Flu (influenza)

Question 1

What is flu?

Answer 1

An acute respiratory illness caused by the RNA virus, influenza viruses

Question 2

How many types of Influenza viruses are there? Which one is most virulent? and Which one occurs more frequently

Answer 2

• 3 types of influenza viruses:
  
  • Influenza A - occurs more frequently and is more virulent (its potential to cause symptoms); causes local outbreaks or pandemics; causes more severe illness (complicated influenza)
  • Influenza B - often circulates along with type A during the yearly outbreaks, but it causes less severe illness
  • Influenza C - causes a mild/ asymptomatic infection similar to common cold

Question 3

Influenza A serotypes are further categorised by their surface antigens. What are the surface antigens?

Answer 3

• Haemagglutinin (H)
• Neuraminidase (N)

Question 4

Why is flu also known as ‘seasona influenza’?

Answer 4

Influenza usually occurs during winter months (December - March)

Question 5

Give 3 complications of influenza in adults?

Answer 5

• Acute bronchitis
• Pneumonia
• Exacerbation of asthma or COPD
• Acute otitis media
• Acute sinusitis

Question 6

Why is there a need for a new influenza vaccine every year?

Answer 6

Because the influenza viruses can mutate through antigenic shift and antigenic drift to produce new strains of influenza, therefore you need new vaccines for the new strains

Question 7

What is Antigenic shift ?

Answer 7

The process by which 2 or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype carrying a mixture of the surface antigens of the two or more original strains

Question 8

What is Antigenic drift?

Answer 8

A process by which mutations of surface antigens on a virus produce a new strain of the original virus

Question 9

What are the clinical features of flu?

Answer 9

• Symptoms appear abruptly, around 2 days after exposure
  
  • Uncomplicated influenza
    
    • Coryzal symptoms - nasal congestion, nasal discharge, dry cough, sore throat
    • Generalised symptoms: fever, headache, myalgia, arthalgia, cervical lymphadenopathy
    • GI symptoms: N&V and diarrhoea
    • Eye symptoms: photophobia, conjunctivitis, pain on eye movement
  • Complicated influenza
    
    • Signs and symptoms requiring hospital admission e.g. sepsis
    • Lower respiratory tract infection causing hypoxaemia, dyspnoea, lung infiltrate
    • CNS involvement
    • Exacerbation of an underlying medical condition e.g. asthma or COPD

Question 10

Give 3 differential diagnoses for flu

Answer 10

• Common cold - causes more nasal problems; fever, headache, myalgia, arthralgia are less common; symptoms are also less severe
• Strep throat - more severe throat pain; absence of cough, sneeze and nasal congestion
• Meningitis - In infants and babies: high fever, staring expression, high-pitched crying, bulging fontanelle, vomiting. In adults: fever, headache, photophobia, neck stiffness, non-blanching rash

Question 11

What investigation(s) would you order for flu in primary care?

Answer 11

• Clinical diagnosis
• However, in cases of complicated influenza, offer rapid antigen tests

Question 12

How would you manage a patient with influenza in primary care?

Answer 12

• Give Oral oseltamivir if all of the following apply:
  
  • The national surveillance scheme indicates that influenza is circulating
  • The person is in an ‘at risk’ group, or the person who was previously healthy is at serious risk of developing complications from influenza
  • The person can start treatment within 48 hrs of symptom onset
• ‘At risk’ group
  
  • Includes people > 65 yrs, children < 6 months, pregnant women, and people with any of the following conditions:
    
    • Chronic heart disease
    • CKD
    • Chronic liver disease
    • Chronic neurological conditions
    • Diabetes
    • Immunosuppression
    • BMI 40 or more
• For uncomplicated influenza
  
  • If previously healthy - no antiviral treatment is needed unless at serious risk of developing complications from influenza
  • If severely immunosuppressed, and the dominant strain has a high risk of oseltamivir resistance e.g. H1N1, give inhaled zanamivir. However, if low risk of resistance, stick with oral oseltamivir
• For complicated influenza:
  
  • If not severely immunosuppressed - prescribe oral oseltamivir
  • If severely immunosuppressed, and the dominant strain has a high risk of oseltamivir resistance e.g. H1N1, give inhaled zanamivir. However, if low risk of resistance, stick with oral oseltamivir

Question 13

What advice would you give to someone with influenza?

Answer 13

Advice:

• Adequate fluid intake to avoid dehydration + plenty of rest
• Paracetamol or ibuprofen as antipyretic and analgesia
• Stay off work or school if unwell
• Symptoms of uncomplicated influenza usually resolve after 1 week
• Educate patients on the symptoms of complicated influenza and advise them to seek medical advice if their condition deteriorates or if no improvement after 1 week

Question 14

When should you admit a person with influenza?

Answer 14

• Pneumonia
• Co-morbidities that increase risk of complications e.g. diabetes
• An alternative diagnosis is suspected