Influenza

Question 1

What causes influenza?

Answer 1

The influenza virus, part of the orthomyxoviridae family.

Comes in groups A, B & C
IfA - mammals and birds
IfB/C - Only affect humans

Question 2

Most influenza is seasonal, occurring during the winter months, why do we think that is?

Answer 2

Several theories:

• Vit D prevents viral infections
• Solar radiation mutates viral RNA creating new strains

Question 3

Describe the structure of the influenza virus?

Answer 3

Two major Surface Antigens:

• Neuraminidase (N) enables new virus release from host cell
• Haemaglutinin (H) enables viral entry to host cell

Question 4

How are new influenza strains produced?

Answer 4

By antigenic drift - small changes to the H/N layout over time hence why we get epidemics and need new vaccines every year

By Antigenic Shift - Abrupt major change to the H/N layout due to combination of 2 strains and reassortment of the viral gene segments –> Creating flu strains that jump species causing pandemics

Question 5

Give an example of influenza antigenic shift?

Answer 5

Combination of Human/Avian influenza to form the swine flu pandemic.

Question 6

How is influenza transmitted?

Answer 6

1) Droplet
2) Direct person-person contact
3) Indirect person-fomite-person contact (the virus can survive 48 hrs on non-porous surfaces)

Avian flu is also transmitted by contact with infected birds (dead or alive)

Question 7

Risk factors for a flu infection?

Answer 7

• Existing disease (neuro/hepatic/renal/cardiac/pulm)
• Immunocompromise incl. DM
• > 65 yrs or <6months
• Pregnancy- including 2 weeks after birth
• Morbid Obesity

Question 8

How does influenza present?

Answer 8

Abrupt high fever lasting 3 days 
Plus 2 or more of:
- Cough
- Sore throat or rhinorrhoea
- Myalgia
- Headache
- Malaise

Less often they may get N&V + Diarrhoea

Question 9

How do you test someone for Influenza infection?

Answer 9

1) Viral swabs for PCR & molecular detection
2) CXR in case of pneumonia
3) Blood Cultures
4) Pulse Oximetry & Resp rate
5) U&Es, FBC & CRP

Question 10

A major complication of Influenza is Secondary Bacterial Pneumonia, what do we do if we suspect it?

Answer 10

CURB65 Score:

• Confusion
• Urea >7mmol/l
• Resp Rate >30
• BP <60D OR <90S
• > 65yrs`

Question 11

How do we treat Influenza?

Answer 11

If its complicated or at risk e.g. immunosuppressed give them antivirals within 48hrs:
Specifically Neuraminidase inhibitors i.e:
- Oral Oseltamavir (5 days)
- Inhaled Zanamivir (10 days)
- Peramivir

Question 12

What defines complicated Influenza?

Answer 12

• Hospitilisation
• Affects the LRT
• Affects the CNS
• Exacerbates an underlying condition

Question 13

How do you treat pregnant influenza?

Answer 13

Oral Oseltamavir

Question 14

At what point is influenza considered non-infectious?

Answer 14

• 24 hrs after the last symptoms
• When anti-viral therapy is completed

Whichever’s first

Question 15

How do we prevent the spread of influenza within hospital?

Answer 15

Staff should use:

• Face masks
• Plastic Apron
• Gloves
• Hand Hygiene

If doing an aerosolising procedure e.g. nebuliser or NIV then use a Gown, Eye protection and a FPP3 respiratory mask.

Question 16

How is the flu vaccine produced?

Answer 16

It changes every year based on the 3 most common strains that year, (2 type A & 1 type B).
Its contraindicated in egg allergies as its grown in chick embryos.

Question 17

What are the major complications of Influenza?

Answer 17

Respiratory
-Acute bronchitis
-SEcondary Bacterial 
-Pneumonia 
Cardiac 
-Myocarditis
-Pericarditis 

CNS

• Guillain-Barre
• Transverse myelitis
• Encephalitis
• Myositis and myoglobinuria

Question 18

Describe the differences between seasonal flu and pandemic flu

Answer 18

Seasonal occurs every winter affecting 10% of the pop and is largely non-lifethreatening in the healthy.

Pandemic flu occurs ~3/century affecting >25% of the pop. and is dangerous with frequent complications.

Question 19

What defines a pandemic?

Answer 19

Effect humans
Be new to the pop.
Show efficient human-human transmission

Question 20

What is an influenza like illness?

Answer 20

A fever and cough that onsets within the last 10 days.

IF its severe enough to warrant hospitlization its called Severe Acute Respiratory Infection (SARI)

Question 21

viral shedding and viral survival in influenza

Answer 21

Virus shedding- release of progeny
• First 4 days
• Longer in children and immunocompromised

Virus Survival
• 24-48 hours on non-porous surfaces
• 8-12 hours on porous surface e.g. tissue