Influenza (RESP)

Question 1

Define influenza.

Answer 1

Acute respiratory tract infection typically caused by seasonal influenza A/B(/C) virus

Question 2

When do most infections of influenza occur?

Answer 2

During the winter season

Question 3

How is influenza A&B spread?

Answer 3

Via person-to-person transmission directly through respiratory droplets, and indirectly through contact with contaminated surfaces

Question 4

How is influenza A classified into various subtypes?

Answer 4

Based on glycoproteins of viral envelope:
- haemagglutinin (H) - H1, H2, H3
- neuraminidase (N) - N1, N2
This allows for a number of different combinations (and antibodies to one subtype of H/N antigen do not react with another type of H/N antigen)

Question 5

What can prevent the spread of influenza? (2)

Answer 5

• hygiene precautions
• vaccination

Question 6

How is influenza characterised?

Answer 6

By upper and lower respiratory tract symptoms

Question 7

Compare outbreaks of influenza A vs B vs C.

Answer 7

• influenza A - annual local outbreaks OR larger epidemics of varying intensity every 2-3y, or occasional pandemics
• influenza B - outbreaks every 4y, milder than influenza A
• influenza C - not associated with epidemics/pandemics, mild

Question 8

What is the role of interferons in influenza?

Answer 8

Interferons are produced by infective cells to stimulate the production of IFGs which can prevent further viral infection and spreading

Question 9

What subtype of influenza A is highly pathogenic?

Answer 9

H1N1 - zoonotic, absence of prior immunity

Question 10

What are the clinical features of influenza? (8)

Answer 10

• fever
• cough (acute bronchitis)
• sore throat
• dyspnoea
• headache
• arthralgia
• myalgia
• fatigue and malaise

Question 11

What might be seen on examination of influenza?

Answer 11

Cervical lymphadenopathy

Question 12

What is the more likely differential if influenza presents with diarrhoea?

Answer 12

Viral gastroenteritis

Question 13

What are some risk factors for influenza? (11)

Answer 13

• winter season
• current influenza outbreak
• unvaccinated
• age >65 or <5
• CVD/respiratory conditions
• diabetes
• haemoglobinopathy
• immunocompromised
• CKD
• pregnancy
• carers/healthcare workers

Question 14

How is influenza usually diagnosed?

Answer 14

Clinical diagnosis - further testing only indicated when results are likely to affect diagnosis and Rx decisions

Question 15

What is the main investigation to consider for influenza?

Answer 15

Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR)

Question 16

When do we do CXR for influenza?

Answer 16

To exclude pneumonia (lobar consolidation, interstitial infiltrates, cavitations)

Question 17

What are some differential diagnoses for influenza? (5)

Answer 17

• COVID-19 (RT-PCR, loss of taste/smell, contacts)
• RSV infection (most common cause <1y, URTI&LRTI symptoms, rapid assays, bronchiolitis, give dexamethasone)
• parainfluenza virus (culture from nasopharynx/LRT, rapid antigen detection, PCR assays)
• bacterial pneumonia (sputum, dyspnoea, CXR with infiltrates, lobar consolidation)
• viral gastroenteritis (diarrhoea)

Question 18

What can we give as prophylaxis for influenza in at-risk groups?

Answer 18

• antiviral therapy - neuraminidase inhibitors, inhibit release of virus from host cells (can also give in acute infection)
  
  • Oseltamivir (Tamiflu) if <3mo
  • Zanamivir if >5y
  • Baloxavir/Marboxil if >5y
• vaccination (Sep-Nov):
  
  • children: live vaccine
  • elderly/at-risk: inactivated vaccine
  • important as different contraindications

Question 19

Who should influenza vaccines NOT be given to?

Answer 19

Acute unwell patients - wait until recovered

Question 20

How do we manage acute influenza?

Answer 20

• supportive care: analgesia, antipyretics, fluids, oxygen (paracetamol not ibuprofen as greater risk adverse effects)
• complicated disease/complication risk: antiviral therapy
  
  • oseltamivir (Tamiflu)
  • zanamivir
  • peramivir
  • baloxivir marboxil
• bacterial infection: broad-spectrum Abx therapy
  
  • complication of bacterial pneumonia –> ceftriaxone
  • suspected S. aureus superinfection –> omaxicillin, vancomycin

Question 21

What are some complications of influenza?

Answer 21

• bacterial pneumonia
• viral pneumonia (symptoms persist)
• otitis media
• rhabdomyolysis/myositis (sore muscles)
• encephalitis
• transverse myelitis (Rx parenteral corticosteroids)
• aseptic meningitis
• Guillain-Barre syndrome (Rx parenteral corticosteroids and Ig infusions)
• toxic shock syndrome
• myocarditis
• post-influenza encephalopathy