Influenza Flashcards
What months is influenza predominant in the northern and southern hemisphere?
northern = Dec-Feb Southern = Jun-Aug
How often do severe epidemics occur? What is this linked to?
every 11 years
sunspot activity - radiation
What is the suns influence in terms of influenza?
radiation may cause mutations leading to antigenic shifts in viral RNA
What year was Spanish flu?
1918/19
What are the 3 main groups of virus and what species do they infect?
A = mammals and birds
B and C = only humans
Describe the influenza virus
RNA virus
8 segment genome
Orthomyxoviridae family
Name the 2 surface proteins on the influenza virus
H and N
H surface protein role
Facilitates viral attachment and entry to host cell
N surface protein role
Enables new virion to be released from host cell
How many different H antigens are there and which are found in humans?
18
1-3 in humans
How many different N antigens are there?
11
Explain antigenic drift
continual point mutations over time at antibody binding sites which may change the antigenic properties and lead to vaccine mismatch and the immune system not combatting the virus as well
Explain antigenic shift
Abrupt major change in virus leading to new H/N combinations leading to pandemics as the virus can go between species
3 requirements for a pandemic
efficient person to person transmission
human pathogenicity
new virus antigenic shift in a susceptible population
Differences between seasonal and pandemic flu
seasonal happens every year in the winter months with 10-15% affected and not life threatening
pandemics occur sporadically affecting 25%+ of population and more serious
How does Avian flu spread?
direct contact with dead or alive infected birds
rarely person to person contact eg carers
Clinical features of flu
abrupt fever of up to 41 degrees for 3 days
plus 2 of: cough, myalgia, headache, malaise
Who definition of influenza like illness
fever - >38 degrees
cough - within last 10 days
If hospitalisation is required what term instead of influenza like illness is used?
severe acute respiratory illness
3 modes of transmission for flu
Airborne - person to person by large droplets >5microns
Contact - direct or indirect (fomite)
When does viral shedding occur and what groups of people is it longer in?
first 4 days of illness
young and immunocompromised
Virus survival on porous and non-porous surfaces
non porous: 24-48hours
porous: 8-12 hours
7 risk factors for complicated influenza
diabetes mellitus children under 6 months morbid obesity severe immunosuppression pregnancy and up to 2 weeks post partum >65 neurological, hepatic, renal, pulmonary and chronic cardiac disease
Common respiratory complications of influenza
acute bronchitis
secondary bacterial pneumonia
Causative organisms of secondary bacterial pneumonia
staph aureus
strep pneumonia
H. influenza
Less common complications of flu
Guillian Barre
myocarditis
primary viral pneumonia
Briefly explain encephalitis lethargica
1918 following flu pandemic
fever, headache, lethargy, postencephalitic parkinsonism
serology +ve flu A
6 diagnosis and investigations for flu
viral nose and throat swabs - PCR blood culture CXR pulse oximetry respiratory rate U+E, FBC, CRP
If a patient with flu has had flu symptoms and fever > 4 days and suspect secondary bacteria pneumonia what should you do?
urgent CXR
When should you start antiviral therapy?
ASAP and within 48 hours of onset
Name 2 neuraminidase inhibitors
oseltamivir
zanamivir
Route of admission and side effects of oseltamivir
oral
nausea, vomit and diarrhoea
Route of admission and side effects of zanamivir
inhaled
occasional bronchospasm
Name 2 other antiviral therapies and briefly describe them
peramivir - neuroaminidase inhibitor given IV in complicated influenza
Favipir - viral RNA polymerase inhibitor given orally
When do immunocompetent adults become non infectious?
24 hours after last symptom, or after last dose of antiviral
whichever is longer
When do immunocompromised or young children become non infectious?
consider each case separately
4 ways healthcare workers protect themselves when in contact with people with flu
wash hands after and use face-fit FFP3 respirator mask for those with a nebuliser
surgical face mask
plastic apron
gloves
Describe briefly the seasonal flu vaccine
prepared each year depending on most likely
circulating strains and is trivalent - 2 type A and 1 B
How is the seasonal flu vaccine prepared?
grown in allantoic cavity of chick embryos - CI in egg allergy
volume and route of administration of flu vaccine
0.5ml
arm im
3 reasons why healthcare workers should get flu vaccines
protect them and families
reduce risk to at risk patients
reduce absence from work during influenza surge activity
