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Infection > Influenza > Flashcards

Influenza Flashcards

1
Q

Antigenic drift

A
  • Mechanism of genetic variation within the virus
  • Occurs continually over time, small on-going point mutations in the genes coding for antibody binding-sites
  • 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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2
Q

Antigenic shift

A
  • Abrupt major change in the virus, resulting in new H/N combinations
  • 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
  • Reassortment of the virus’ gene segments
  • With new antigenic properties the population at risk is unprotected and this can lead to pandemics
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3
Q

Difference between season flu and pandemic flu

A

Seasonal flu- occurs every winter
Pandemic flu- occurs sporadically

Seasonal flu- affects 10-15% of the population
Pandemic flu- affects 25%+ of the population

Seasonal flu- usually unpleasant but not life threatening
Pandemic flu- more serious, more complications

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4
Q

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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5
Q

Influenza transmission

A

-Airborne
– person to person by large droplets >5 microns
-Contact
– direct (person to person)
– indirect (person to fomite to person)

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6
Q

Virus shedding

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

- Longer in young children & immunocompromised

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7
Q

Virus survival

A
  • 24-48 hours on non-porous surfaces

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

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8
Q

Risk factors for complicated influenza

A
  • age -over 65 years or under 6 months
  • severe immunosuppression
  • diabetes mellitus
  • pregnancy (including up to 2 weeks post partum)
  • neurological, hepatic, renal, pulmonary and chronic cardiac disease
  • morbid obesity (BMI >40)
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9
Q

Common complications of the flu

A
  • acute bronchitis
  • secondary bacterial pneumonia (~20%)
    - appears 4-5 days after start of flu
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10
Q

Less common respiratory complications of the flu

A

Primary viral pneumonia

  - appears common in human cases of avian influenza (H5N1)
  - rapid respiratory failure; within 48 hours
  - mortality >40%; within 7 days
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11
Q

Less common cardiac complications of the flu

A

Myocarditis/pericarditis

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12
Q

Less common CNS complications of the flu

A
  • Guillain-Barre

- Myositis & Myoglobinuria

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13
Q

Influenza investigations

A
  • Viral nose and throat swabs/VTS (Molecular detection /PCR; using flocked swans)
  • 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)
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14
Q

Severity assessment of bacterial pneumonia

A 
CURB-65
-Confusion
-Urea >7mmol/l
-Respiratory rate >30mm
-Blood Pressure (diastolic <60 or systolic <90)
->65 years of age
Risk of death in the next 30 days
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15
Q

Protection for healthcare staff

A

-Surgical face mask
-Plastic apron
-Gloves
Wash hands after any examination

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16
Q

Antiviral therapy

A
  • use ASAP and within 48hours of symptom onset
  • in complicated illness should always be given, no matter how long after onset of illnes
  • Oseltamivir (tamiflu)- oral
  • Zanamivir (relenza)- inhaled or iv
17
Q

Antiviral therapy in pregnancy

A
  • Antivirals have been recommend due to the adverse outcomes in this group
  • Oseltamivir remains first line option…
  • Recent studies (2014) suggests there is no evidence of harm of either oseltamivir or zanamivir
18
Q

Antiretroviral therapy for breastfeeding

A
  • Only tiny amounts of Oseltamivir in milk

- Current guidance is – Oral Oseltamivir

19
Q

When does an individual become non-infectious?

A

Immunocompetent adults
-24hrs after last ‘flu symptoms (fever & cough)
-Or when anti-viral therapy completed
Which ever is longer

20
Q

Seasonal Flu vaccine

A
  • Prepared each year using viruses considered most likely to be circulating in the forthcoming winter
  • Grown in chick embryos (therefore C.I. in those with egg allergy)
  • Chemically inactivated and purified, trivalent vaccines containing 2 type A & 1 type B subtype viruses
  • Single 0.5 ml intramuscular injection
21
Q

Why should healthcare workers be vaccinated?

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

Infection (15 decks)

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