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- including 2 weeks after birth
- 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)
- Peramivir
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 first
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?
Respiratory -Acute bronchitis -SEcondary Bacterial -Pneumonia Cardiac -Myocarditis -Pericarditis
CNS
- Guillain-Barre
- Transverse myelitis
- Encephalitis
- Myositis and myoglobinuria
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)
viral shedding and viral survival in influenza
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
