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Systems: Infection AB > Influenza > Flashcards

Influenza Flashcards

1
Q

When does seasonal flu occur?

A

During the Winter months

  • Dec – Feb in the Northern Hemisphere
  • Jun – Aug in the Southern Hemisphere
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2
Q

What is the ‘link’ between the flu and the sun?

A
  • 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
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3
Q

What flu pandemics have taken place?

A
  • Spanish flu
  • Asian flu
  • Hong Kong flu
  • Swine flu
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4
Q

What is the structure of the influenza virus?

A
  • RNA virus with 8 segment genome
  • Part of the orthomyxoviridae family
  • Three main groups: A (mammals and birds,B (humans),C(humans)
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5
Q

What are the 2 types of surface proteins on the influenza virus?

A
  • Haemagglutinin (H)

- Neuraminidase (N)

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6
Q

What does the haemagglutinin surface protein on the influenza virus do?

A

Facilitates viral attachment and entry to host cell

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7
Q

What does the neuraminidase surface protein on the influenza virus do?

A

Enables new virion to be released from host cell

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8
Q

How are there so many strains of flu?

A
  • 18 different H antigens (H1-3 in humans)

- 11 different N antigens

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9
Q

What is antigenic drift?

A
  • 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

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10
Q

What can antigenic drift lead to?

A
  • May change the antigenic properties and eventually the immune system will not combat the virus as well
  • Causes worse than normal epidemics & vaccine mismatch
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11
Q

What is antigenic shift?

A
  • An abrupt major change in the virus, resulting in new H/N combinations
  • Reassortment of the virus gene segments
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12
Q

What does antigenic lead to?

A
  • 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
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13
Q

How can antigenic shift lead to pandemics?

A

With new antigenic properties the population at risk is unprotected and this can lead to PANDEMICS

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14
Q

How does pandemic flu differ from seasonal flu?

A 
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
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15
Q

What are the requirements for a pandemic?

A
  • Human pathogenicity
  • ‘New’ virus (antigenic shift)=susceptible population
  • Efficient person-person transmission
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16
Q

How does mortality vary with age?

A

Greatest mortality in the young and old

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17
Q

What strains of avian flu have affected humans?

A
  • H5N1

- H7N9

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18
Q

How does avian flu spread?

A
  • 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
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19
Q

What are the clinical features of influenza?

A
  • 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
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20
Q

What is the WHO definition of influenza like illness?

A
  • Fever (>38C) AND
  • Cough
  • Onset within the last 10 days
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21
Q

How is influenza like illness defined if it requires hospitalisation?

A

Severe acute respiratory infection (SARI)

22
Q

What are the symptoms of swine flu?

A

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
23
Q

How is flu transmitted?

A
  • Airborne: person to person by large droplets >5 microns
  • Direct contact: person to person
  • Indirect contact: person to fomite to person
24
Q

How long does virus shedding occur for?

A
  • First 4 days of illness (range 1-7 days)

- Longer in young children & immunocompromised

25
Q

How long can the virus survive for?

A
  • 24-48 hours on non-porous surfaces

- 8-12 hours on porous surface e.g. tissue

26
Q

Who are the high risk groups for complicated influenza?

A
  • 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)
27
Q

What are the common respiratory complications of influenza?

A
  • Acute bronchitis

- Secondary bacterial pneumonia (appears 4-5 days after the start of flu)

28
Q

What are the less common complications of flu?

A
  • Primary viral pneumonia (common in avian flu and leads to rapid respiratory failure and death)
  • Myocarditis/pericarditis
  • Transverse myelitis/Guillain Barre
  • Myositis and myoglobulinuria
29
Q

How does encephalitis lethargica present?

A
  • Fever, headache
  • External ophthalmoplegia
  • Lethargy
  • Sleep reversal
  • Postencephalitic Parkinsonism
30
Q

What is the serology of encephalitis lethargica?

A

+ve flu A

31
Q

What investigations should be carried out for flu?

A
  • 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)
32
Q

How is secondary bacterial pneumonia assessed?

A 
CURB 65 score
-Confusion
-Urea> 7mmol/l
-Respiratory rate >30
-Blood pressure (diastolic<60 or systolic<90)
>65 years old
33
Q

What should patients with flu like symptoms and a fever for >4 days receive?

A

Urgent CXR

-Suspected secondary bacterial pneumonia

34
Q

Give examples of neuraminidase inhibitors.

A
  • Oseltamivir

- Zanamivir

35
Q

How should antiviral therapy be administered?

A
  • Use ASAP, within 48 hours of symptom onset

- In complicated illness, should always be given no matter how long after the onset of illness

36
Q

How is oseltamivir (Tamiflu) given?

A
  • Oral
  • Over 13 years
  • 75mg every 12 hours fro 5 days
37
Q

How is anamivir (Relenza) given?

A
  • Inhaled
  • Available only as a dry powder inhaler
  • Over 12 years
  • 10mg inhaled daily for up to 10 days
38
Q

What are the adverse effects of Tamiflu?

A

Common
-Nausea, vomiting, abdominal pain, diarrhoea

Less common
-Headache, hallucinations, insomnia and rash

Cautions
-Renal dosing needed

39
Q

What are the adverse effects of Relnza?

A

Rare but occasional bronchospasm

40
Q

Why are antadine and rimantadine no longer used as antiviral therapies?

A

Due to resistance

41
Q

What is peramivir?

A

A neuroaminidase inhibitor given as an IV infusion for uncomplicated influenza

42
Q

What is favipiravir?

A

A viral RNA polymerase inhibitor given as an oral medication for re-emerging viruses in Japan

43
Q

How is flu managed in pregnancy?

A
  • Antivirals recommended

- Tamiflu (oseltamivir) first line option

44
Q

How is flu managed in breast feeding?

A

Oral oseltamivir

45
Q

When does an individual become non-infectious?

A

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

46
Q

How should healthcare staff protect themselves from patients with proven or suspected flu?

A
  • Surgical face mask
  • Plastic apron
  • Gloves
  • Wash hands after any examination
  • Use of face life FFP3 respirator mask when seeing patients on nebulisers
47
Q

Why is the seasonal flu vaccine contraindicated in those with egg allergies?

A

Grown in allantoic cavity of chick embryos

48
Q

How is the seasonal flu vaccine created?

A
  • Prepared each year using viruses considered most likely to be circulating in the forthcoming winter
  • Chemically inactivated and purified
49
Q

What is the composition of the seasonal flu vaccination?

A

Trivalent

-Containing 2 type A & 1 type B subtype viruses

50
Q

What is the only known adverse effect of the seasonal flu vaccination?

A

Sore arm

51
Q

How is the seasonal flu vaccination administered?

A

Single 0.5ml IM injection

52
Q

Why should healthcare workers have the vaccination?

A
  • To protect themselves and their families
  • To reduce the risk to ‘at risk’ patients
  • To reduce absence from work during influenza ‘surge’ activity

Systems: Infection AB (12 decks)

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