Influenza Flashcards
When do seasonal influenza epidemics peak in the northern hemisphere?
During the winter
Describe the influenza virus
RNA virus part of the Orthomyxoviridae family
Three main groups: A, B and C
How is influenza spread
Rapid person-person spread by aerosolized droplets and contact
Influenza A is subdivided according to what?
Combinations of virus surface proteins
e.g A(H1N1), A(H3N2)
What is antigenic drift?
A mechanism of genetic variation within the virus whereby it changes continually over time through small point mutations
May change the antigenic properties (ways in which the immune system normally detects it) and eventually the immune system will not combat the virus as well
What can happen as a result of antigenic drift?
Worse than normal epidemics
Vaccine mismatch
What is antigenic shift?
Abrupt major change in the virus, resulting in new H/N combinations. It is the process by which 2 or more different strains of a virus, or strains of 2 or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains.
The genetic change that enables a flu strain to jump from one animal species to another
With new antigenic properties the population at risk is unprotected and this can lead to PANDEMICS
What is Haemagglutinin (H) responsible for?
Surface enzyme that facilitates viral attachment and entry to host cell
What is Neuraminidase (N) responsible for?
Surface enzyme that enables new virion to be released from host cell
The human influenza flu (swine flu) pandemic in 2009 was caused by which subtype of influenza?
Influenza A (H1N1)
What was the deadly influenza pandemic that occurred in 1918?
Spanish flu
How is a pandemic influenza different to the seasonal flu that happens every year during winter?
Pandemics occur about three times each century and can arise at any time of year.
Ordinary flu affects about 10-15% of the population whereas a pandemic has affected 25% or more
A pandemic influenza is usually a more serious infection for everyone with more complications.
What does a pandemic require to happen?
Human pathogenicity i.e. a virus, bacterium, prion, or fungus that causes disease in humans
‘New’ virus (antigenic shift) - susceptible population
Efficient person-person transmission
Which strains of avian influenza affect humans?
H5N1
H7N9
How does avian flu spread?
Spreads through direct contact with infected birds, dead or alive
Occasional transmission via close human to human contact (staff, caregivers)
No known transmission by eating properly cooked food/eggs etc
What are the clinical features of influenza?
Note incubation period and symptoms
Incubation period 2-4 days (range 1-7 days)
Abrupt fever up to 41 degrees lasting 3 days
Plus 2 or more of: cough, sore throat, myalgia, headache, malaise
What is influenza like illness (ILI), also known as flu-like symptoms?
A diagnosis of possible influenza or other illness causing these common symptoms:
Fever (>38°C) AND cough
Onset within the last 10 days
How can influenza be transmitted?
Airborne: person-person by large droplets
Contact - direct (person-person) or indirect (person-object-person)
Who is at risk of developing a complicated case of influenza?
Neurological, hepatic, renal, pulmonary and chronic cardiac disease
DM
Severe immunosuppression
Age > 65 years
Pregnancy (including up to two weeks post partum)
Children under 6 months of age
Morbid obesity (BMI ≥40)
Common respiratory complications associated with influenza (2) ie what do patients commonly develop after having influenza infection
Acute Bronchitis
Secondary bacterial pneumonia
Less common general complications associated with influenza
Primary viral pneumonia
Rapid respiratory failure
Myocarditis/pericarditis
CNS: Transverse myelitis/Guillain-Barre
or Myositis & Myoglobinuria
Diagnosis and investigations for influenza
Viral nose and throat swabs/VTS (Molecular detection /PCR; using flocked swabs)
CXR – pneumonitis/pneumonia/ARDS
Blood culture
Pulse oximetry – SpO2 <92% need ABG and oxygen
Respiratory rate !
U & E’s, FBC, CRP (CRP monitoring recovery of pneumonia - should halve in 4 days)
Which scoring tool is used to assess the severity assessment for pneumonia?
CURB 65
Confusion
Urea >7mmol/L
Resp rate >30
BP - diastolic <60 or systolic <90
> 65 years of age
5/5 = 57% risk of death in next 30 days
What are neuraminidase inhibitors?
A class of anti-viral drug.
They block the neuraminidase enzyme on the surface of viruses. This prevents its reproduction by budding from the host cell
When should anti-virals be administered?
ASAP and within 48 hours of symptom onset.
In complicated illness, give them regardless of timing.
Name 2 common anti-viral drugs
1st line Oseltamivir (oral)
2nd line - Zanamivir (inhaled or I.V)
What is considered ‘complicated influenza’?
Influenza requiring hospital admission and/or with symptoms and signs of LRTI, CNS involvement and/or a significant exacerbation of an underlying medical condition
Current guidelines on antiviral therapy during pregnancy?
Antivirals have been recommended due to the adverse outcomes in this group
Oseltamivir remains first line option
When does an individual become non-infectious?
In immunocompetent adults - 24 hours after last flu symptoms or when anti-viral treatment is complete
In immunocompromised adults + young children - consider each case seperately
