Influenza Flashcards
when does influenza occur and why is it said to be related to the sun?
From the latin word ‘influentia’ – meaning influence of the stars
Seasonal influenza occurs during winter months:
Dec – Feb in the Northern Hemisphere
Jun – Aug in the Southern Hemisphere
More severe epidemics of influenza occur every 11 years; same as increased ‘sunspot activity’
what are 20th century pandemics of influenza?
1918-9 ‘Spanish Flu’ (A/H1N1)
† 20-100 million deaths
1957-8 ‘Asian Flu’ (A/H2N2)
† 1-1.5 million deaths
1968-9 ‘Hong Kong Flu’ (A/H3N2)
† 0.75-1 million deaths
2009-10 ‘Swine Flu’ (A/H1N1)
† approximately 285.000 deaths
describe the surface proteins of influenza?
what is the mechanism of 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
what is the mechanism of 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
how do seasonal and pandemic flu differ?
what are the requirements for a pandemic?
Human pathogenicity
‘New’ virus (antigenic shift)
- susceptible population
🗹 Efficient person-person
transmission
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
ifluenza like illness?
Fever (>38°C) and
Cough
Onset within the last 10 days
(if requires hospitalization defined as severe acute respiratory infection (SARI))
symptoms of swine flu?
how is influenza transmitted?
Airborne – person ⭢ person by large droplets >5 microns
Contact – direct (person ⭢ person)
– indirect (person ⭢ fomite ⭢ 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
what are risk factors for complicated influenza?
Neurological, hepatic, renal, pulmonary and chronic cardiac disease
Diabetes mellitus
Severe immunosuppression
Age over 65 years
Pregnancy (including up to two weeks post partum)
Children under 6 months of age
Morbid obesity (BMI ≥40)
what are common respiratory complications of influenza?
Acute Bronchitis
Secondary Bacterial Pneumonia (~20%)
Appears 4-5 days after start of ‘flu
RESPIRATORY:
Primary viral pneumonia
- appears common in human cases of avian influenza (H5N1)
- rapid respiratory failure; within 48 hours
- mortality >40%; within 7 days
CARDIAC:
Myocarditis/pericarditis
CNS:
Transverse myelitis/Guillain-Barre
Myositis & Myoglobinuria
ENCEPHALITIS LETHARGICA
Fever, headache
External ophthalmoplegia
Lethargy
Sleep reversal
25 % mortality
Postencephalitic Parkinsonism
Serology +ve ’flu A
Paralleled 1918-19 pandemic
what diagnosis and investigations should be done for influenza?
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)
sECONDARY BACTERIAL PNEUMONIA
Patients with ‘flu symptoms and a fever for > 4days – should have an urgent CXR
Severity assessment – use C(U)RB-65 score
Confusion
Urea >7mmol/l
Respiratory rate >30mm
Blood Pressure (diastolic <60 or systolic <90)
>65 years of age
C(U)RB score: Risk of death in the next 30 days (0=0.6%, 1=3.2%, 2=13%, 3=17%, 4=41.5%, 5=57%)
ANTIVIRAL THERAPY
Use ASAP and within 48hours of symptom onset !
But, in complicated illness: “…should always be given, no matter how long after onset of illness…”
OSELTAMIVIR (TAMIFLU) - Oral
Dose : Over 13 years – 75mg every 12 hours for 5 days
Adverse Effects:
Common – Nausea, vomiting, abdominal pain, diarrhoea
Less Common – Headache, hallucinations, insomnia and rash
Cautions: Renal dosing needed
ZANAMIVIR (RELENZA) – Inhaled & or I.V.
Available only as a dry powder inhaler
Dose: Over 12 years – 10mg inhaled daily for up to 10 days
Adverse Effects: Rare – occasional bronchospasm
OTHER ANTIVIRAL THERAPY
Peramivir (Alpivab®)
Neuroaminidase inhibitor
Licensed in USA and approved by European Medicines Agency (EMA) 1st May 2018 !
Intravenous infusion, for uncomplicated influenza
Favipiravir (Avigan®, Toyama Chemicals Ltd)
Viral RNA polymerase inhibitor
Licenced in Japan for ‘re-emerging influenza viruses’
Oral medication
Baloxavir Marboxil (Xofluza®, Roche)
Endonuclease inhibitor
One single dose
(Amantadine & Rimantadine notl used due to resistance)
BREASTFEEDING
Only tiny amounts of Oseltamivir in milk
Current guidance is – Oral Oseltamivir
PREGNANCY
Current guidance (PHE Sep 2017) is:
Antivirals have been recommended…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
FDA pregnancy category C: No malformation, maternal toxicity or embryotoxcity were observed in animal studies. No data available in humans.
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
PROTECTION FOR HEALTHCARE STAFF
For most patients with proven or suspected ‘flu’
Surgical face mask
Plastic apron
Gloves
Wash hands after any examination
Seeing patients who are receiving a Nebuliser, NIV etc – with aerosolised virus
‘Face-fit’ FFP3 respirator mask
VACCINATION
Seasonal Flu vaccine’
