Influenza Flashcards
Antigenic drift
- 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
Antigenic shift
- 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
Difference between season flu and pandemic flu
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
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
Influenza transmission
-Airborne
– person to person by large droplets >5 microns
-Contact
– direct (person to person)
– indirect (person to fomite to person)
Virus shedding
- First 4 days of illness (range 1-7 days)
- Longer in young children & immunocompromised
Virus survival
- 24-48 hours on non-porous surfaces
- 8-12 hours on porous surface e.g. tissue
Risk factors for complicated influenza
- 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)
Common complications of the flu
- acute bronchitis
- secondary bacterial pneumonia (~20%)
- appears 4-5 days after start of flu
Less common respiratory complications of the flu
Primary viral pneumonia
- appears common in human cases of avian influenza (H5N1) - rapid respiratory failure; within 48 hours - mortality >40%; within 7 days
Less common cardiac complications of the flu
Myocarditis/pericarditis
Less common CNS complications of the flu
- Guillain-Barre
- Myositis & Myoglobinuria
Influenza investigations
- 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)
Severity assessment of bacterial pneumonia
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
Protection for healthcare staff
-Surgical face mask
-Plastic apron
-Gloves
Wash hands after any examination
Antiviral therapy
- 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
Antiviral therapy in pregnancy
- 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
Antiretroviral therapy for breastfeeding
- Only tiny amounts of Oseltamivir in milk
- Current guidance is – Oral Oseltamivir
When does an individual become non-infectious?
Immunocompetent adults
-24hrs after last ‘flu symptoms (fever & cough)
-Or when anti-viral therapy completed
Which ever is longer
Seasonal Flu vaccine
- 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
Why should healthcare workers be vaccinated?
- To protect themselves and their families
- To reduce the risk to ‘at risk’ patients
- To reduce absence from work during influenza ‘surge’ activity
