Influenza Flashcards
What causes influenza?
The influenza virus, part of the orthomyxoviridae family.
Comes in groups A, B & C
IfA - mammals and birds
IfB/C - Only affect humans
Most influenza is seasonal, occurring during the winter months, why do we think that is?
Several theories:
- Vit D prevents viral infections
- Solar radiation mutates viral RNA creating new strains
Describe the structure of the influenza virus?
Two major Surface Antigens:
- Neuraminidase (N) enables new virus release from host cell
- Haemaglutinin (H) enables viral entry to host cell
How are new influenza strains produced?
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
Give an example of influenza antigenic shift?
Combination of Human/Avian influenza to form the swine flu pandemic.
How is influenza transmitted?
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)
Risk factors for a flu infection?
- Existing disease (neuro/hepatic/renal/cardiac/pulm)
- Immunocompromise incl. DM
- > 65 yrs or <6months
- Pregnancy
- Morbid Obesity
How does influenza present?
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
How do you test someone for Influenza infection?
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
A major complication of Influenza is Secondary Bacterial Pneumonia, what do we do if we suspect it?
CURB65 Score:
- Confusion
- Urea >7mmol/l
- Resp Rate >30
- BP <60D OR <90S
- > 65yrs`
How do we treat Influenza?
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)
What defines complicated Influenza?
- Hospitilisation
- Affects the LRT
- Affects the CNS
- Exacerbates an underlying condition
How do you treat pregnant influenza?
Oral Oseltamavir
At what point is influenza considered non-infectious?
- 24 hrs after the last symptoms
- When anti-viral therapy is completed
Whichever’s last
How do we prevent the spread of influenza within hospital?
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.
How is the flu vaccine produced?
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.
What are the major complications of Influenza?
Acute bronchitis & SEcondary Bacterial Pneumonia are the most common.
Also Viral Pneumonia, Myocarditis & Guillain-Barre.
Describe the differences between seasonal flu and pandemic flu
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.
What defines a pandemic?
Effect humans
Be new to the pop.
Show efficient human-human transmission
What is an influenza like illness?
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)
