Influenza Flashcards
What kind of virus is influenza?
RNA virus
3 main groups of influenza
A
B
C
What does IfA affect?
Mammals
Birds
What do IfB and IfC affect?
only humans
Surface proteins of influenza
18 different H antigens (H1-3 in humans) = haemagglutinin (H)
11 different N antigens = Neuraminidase (N)
What does haemagglutinin allow?
Viral attachment and entry into the host cell
What do neuraminidases allow?
Enables new virion to be released from host cell
What is antigenic drift?
Mechanism of genetic variation within the virus
What can antigenic drift cause?
Worse than normal epidemics
Vaccine mismatch
Definition of pandemic
Virus spreads across the whole globe
When does pandemic flu occur?
Sporadically - not in usual influenza months
Mortality with pandemics increases with….
age
What strains of avian flu affect humans?
H5N1
H7N9
Transmission of avian flu
Spreads through direct contact with infected birds, dead or alive
Occassional transmission via close human to human contact (staff, caregivers)
Which avian flu strain has the highest mortality in humans?
H5N1
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 + oxygen
Respiratory rate
U and Es, FBC, CRP
Incubation period of influenza
2-4 days (range 1-7 days)
Presentation of influenza
Abrupt fever up to 41C (commonly 38-41) which lasts 3 days (range 1-5 days) 2 or more of - cough - sore throat, rhinorrhoea - myalgia - headache - malaise Predominance of systemic symptoms Less common symptoms - nausea - vomiting - diarrhoea
Definition of influenza like illness (ILI)
Fever >38C AND cough with onset in last 10 days
If influenza illness requires hospitalisation, what is it classed as?
Severe acute respiratory infection (SARI)
Symptoms of swine flu
Sudden fever (>38C) Sudden cough tiredness chills headache sore throat, runny nose, sneezing Diarrhoea, loss of appetite Aching muscles, joint or limb pain
Transmission of influenza
Airborne - person to person by large droplets Contact - direct (person to person) - indirect (person to fomite to person)
When does virus shedding of influenza occur?
First 4 days of illness (range 1-7 days)
Viral survival of influenza
24-48 hours on non-porous surfaces
8-12 hours on porous surfaces e.g. tissue
Risk factors for complicated influenza
Neurological, hepatic, renal, pulmonary and chronic cardiac disease Diabetes mellitus Severe immunosuppression Age > 65 Pregnancy and up to 2 weeks post partum Children < 6 months old Morbid obesity (BMI >_40)
Complications of influenza
Acute bronchitis Secondary bacterial pneumonia (20%) - 4-5 days before the start of the flu Community MRSA uncommon in US/Europe less common - primary viral pneumonia - myocarditis/pericarditis - CNS e.g. Guillian barre
Presentation of encephalitis lethargia
fever headache external opthalmoplegia lethargy sleep reversal
Mortality of encephalitis lethargia
25%
Complications of encephalitis lethargia
Postencephalitic parkinsonism
When does an individual become non-infectious in immunocompetent adults?
Whichever one of the below lasts longer
- 24 hrs after last flu symptoms (fever and cough)
OR
- When antiviral therapy is completed
When should antiviral therapy be given in the treatment of influenza?
ASAP and within 48 hours of symptom onset
In complicated illness - should always be given, not matter how long after onset of illness
Antivirals that can be used to treat influenza
Oseltamivir (Tamiflu) - FIRST LINE
Zanamivir (Relenza) - SECOND LINE
Peramivir
Favipiravir
Can oseltamivir be used in pregnancy for the treatment of influenza?
Yes
What must be worn by healthcare professionals if patient has proven or suspected flu?
Surgical face mask
Plastic apron
Gloves
Who is the seasonal flu vaccine contraindicated to and why?
Those with an egg allergy as the vaccine is grown in the allantoic cavity of chick embryos
What do seasonal flu vaccines contain?
They are trivalent
- 2 type A subtype viruses
- 1 type B subtype viruses
Why should healthcare workers have the flu vaccine?
To protect themselves and their families
To reduce the risk to ‘at risk’ patients
To reduce absence from work during influenza ‘surge’ activity
