Influenza COPY Flashcards
When does seasonal flu occur?
During the Winter months
- Dec – Feb in the Northern Hemisphere
- Jun – Aug in the Southern Hemisphere
What is the ‘link’ between the flu and the sun?
- More severe epidemics of influenza occur every 11 years; same as increased ‘sunspot activity’
- The sun’s radiation may cause mutations leading to “antigenic shifts’ in viral RNA.
- Theory that Vitamin D levels help to prevent viral infection
What flu pandemics have taken place?
- Spanish flu
- Asian flu
- Hong Kong flu
- Swine flu
What is the structure of the influenza virus?
- RNA virus with 8 segment genome
- Part of the orthomyxoviridae family
- Three main groups: A (mammals and birds,B (humans),C(humans)
What are the 2 types of surface proteins on the influenza virus?
- Haemagglutinin (H)
- Neuraminidase (N)
What does the haemagglutinin surface protein on the influenza virus do?
Facilitates viral attachment and entry to host cell
What does the neuraminidase surface protein on the influenza virus do?
Enables new virion to be released from host cell
How are there so many strains of flu?
- 18 different H antigens (H1-3 in humans)
- 11 different N antigens
What is antigenic drift?
- A mechanism of genetic variation within the virus
- It occurs continually over time, small on-going point mutations in the genes coding for antibody binding-sites
What can antigenic drift lead to?
- May change the antigenic properties and eventually the immune system will not combat the virus as well
- Causes worse than normal epidemics & vaccine mismatch
What is antigenic shift?
- An abrupt major change in the virus, resulting in new H/N combinations
- Reassortment of the virus gene segments
What does antigenic lead to?
- The genetic change that enables a flu strain to jump from one animal species to another
- The process by which two or more different strains of a virus combine to form a new subtype, resulting in new H/N combinations
How can antigenic shift lead to pandemics?
With new antigenic properties the population at risk is unprotected and this can lead to PANDEMICS
How does pandemic flu differ from seasonal flu?
Season flu -Occurs every winter -Affects 10-15 % of the population -Usually unpleasant but not life-threatening
Pandemic flu
- Occur sporadically
- Affects 25% + of the population
- More serious, more complications
What are the requirements for a pandemic?
- Human pathogenicity
- ‘New’ virus (antigenic shift)=susceptible population
- Efficient person-person transmission
How does mortality vary with age?
Greatest mortality in the young and old
What strains of avian flu have affected 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?
- Incubation period 2-4 days (range 1-7 days)
- Abrupt fever up to 41°C (commonly 38-40°C) which lasts 3 days (range 1-5 days)
- Plus 2 or more of: Cough, [sore throat, rhinorrhoea], myalgia, headache, malaise.
- Predominance of systemic symptoms
- Less common symptoms: Nausea, vomiting, diarrhoea
What is the WHO definition of influenza like illness?
- Fever (>38C) AND
- Cough
- Onset within the last 10 days
How is influenza like illness defined if it requires hospitalisation?
Severe acute respiratory infection (SARI)
What are the symptoms of swine flu?
Typical symptoms
-Sudden fever, sudde cough
Other symptoms
- Tiredness, chills
- Headache, sore throat, runny nose, sneezing
- Diarrhoea or stomach upset, loss of appetite
- Aching muscles, limb or joint pain
How is flu transmitted?
- Airborne: person to person by large droplets >5 microns
- Direct contact: person to person
- Indirect contact: person to fomite to person
How long does virus shedding occur for?
- First 4 days of illness (range 1-7 days)
- Longer in young children & immunocompromised
How long can the virus survive for?
- 24-48 hours on non-porous surfaces
- 8-12 hours on porous surface e.g. tissue
Who are the high risk groups for complicated influenza?
- Neurological, hepatic, renal, pulmonary and chronic cardiac disease
- Diabetes mellitus
- Severe immunosuppression
- Age over 65 year
- Pregnancy (including up to two weeks post partum)
- Children under 6 months of age
- Morbid obesity (BMI ≥40)
What are the common respiratory complications of influenza?
- Acute bronchitis
- Secondary bacterial pneumonia (appears 4-5 days after the start of flu)
What are the less common complications of flu?
- Primary viral pneumonia (common in avian flu and leads to rapid respiratory failure and death)
- Myocarditis/pericarditis
- Transverse myelitis/Guillain Barre
- Myositis and myoglobulinuria
How does encephalitis lethargica present?
- Fever, headache
- External ophthalmoplegia
- Lethargy
- Sleep reversal
- Postencephalitic Parkinsonism
What is the serology of encephalitis lethargica?
+ve flu A
What investigations should be carried out for flu?
- Viral nose and throat swabs/VTS (Molecular detection /PCR; using flocked swabs)
- Chest X-ray – 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)
How is secondary bacterial pneumonia assessed?
CURB 65 score -Confusion -Urea> 7mmol/l -Respiratory rate >30 -Blood pressure (diastolic<60 or systolic<90) >65 years old
What should patients with flu like symptoms and a fever for >4 days receive?
Urgent CXR
-Suspected secondary bacterial pneumonia
Give examples of neuraminidase inhibitors.
- Oseltamivir
- Zanamivir
How should antiviral therapy be administered?
- Use ASAP, within 48 hours of symptom onset
- In complicated illness, should always be given no matter how long after the onset of illness
How is oseltamivir (Tamiflu) given?
- Oral
- Over 13 years
- 75mg every 12 hours fro 5 days
How is anamivir (Relenza) given?
- Inhaled
- Available only as a dry powder inhaler
- Over 12 years
- 10mg inhaled daily for up to 10 days
What are the adverse effects of Tamiflu?
Common
-Nausea, vomiting, abdominal pain, diarrhoea
Less common
-Headache, hallucinations, insomnia and rash
Cautions
-Renal dosing needed
What are the adverse effects of Relnza?
Rare but occasional bronchospasm
Why are antadine and rimantadine no longer used as antiviral therapies?
Due to resistance
What is peramivir?
A neuroaminidase inhibitor given as an IV infusion for uncomplicated influenza
What is favipiravir?
A viral RNA polymerase inhibitor given as an oral medication for re-emerging viruses in Japan
How is flu managed in pregnancy?
- Antivirals recommended
- Tamiflu (oseltamivir) first line option
How is flu managed in breast feeding?
Oral oseltamivir
When does an individual become non-infectious?
Immunocompetent adults: whichever is longer
- 24hrs after last ‘flu symptoms (fever & cough)
- Or when anti-viral therapy completed
Immumocomromised adults and young children
-Consider each case separately
How should healthcare staff protect themselves from patients with proven or suspected flu?
- Surgical face mask
- Plastic apron
- Gloves
- Wash hands after any examination
- Use of face life FFP3 respirator mask when seeing patients on nebulisers
Why is the seasonal flu vaccine contraindicated in those with egg allergies?
Grown in allantoic cavity of chick embryos
How is the seasonal flu vaccine created?
- Prepared each year using viruses considered most likely to be circulating in the forthcoming winter
- Chemically inactivated and purified
What is the composition of the seasonal flu vaccination?
Trivalent
-Containing 2 type A & 1 type B subtype viruses
What is the only known adverse effect of the seasonal flu vaccination?
Sore arm
How is the seasonal flu vaccination administered?
Single 0.5ml IM injection
Why should healthcare workers have the vaccination?
- To protect themselves and their families
- To reduce the risk to ‘at risk’ patients
- To reduce absence from work during influenza ‘surge’ activity
