Influenza Flashcards
Describe seasonal influenza
Occurs during winter months
Dec-Feb in Northern Hemisphere
Jun-Aug in Southern Hemisphere
more severe epidemics occur every 11 years, same as increased ‘sunspot activity’
Describe the influenza virus
RNA virus with 8 segment genome
Orthomyxoviridae family
Three main groups;
- A infects mammals and birds
- B only humans
- C only humans
Describe the surface proteins of the influenza virus
18 different H antigens (H1-3 in humans)
- haemaglutinin facilitates attachment and entry to host cell
11 different N antigens
- neuraminidase enables new virion to be released from host cell
Describe antigenic drift in influenza
Mechanism of antigenic variation within virus
Continually occurring, small on-going point mutations in genes coding for antibody-binding sites
May change antigenic properties and immune system will not combat virus as well
Causes wore than normal epidemics and vaccine mismatch
Describe antigenic shift in influenza
Abrupt major change in virus, resulting in new H/N combinations
The genetic change that enables flu strain to jump from one animal species to another
Process by which two or more different strains combine to form new subtype resulting in new H/N combinations
Reassortment of gene segments
Describe the difference between pandemic and seasonal flu
Pandemic; occur sporadically, affects 25%+ of population, more serious, more complications
Seasonal flu; occurs every winter, affects 10-15% of population, usually unpleasant but not life-threatening
What are the requirements of a pandemic?
- Human pathogenicity
- ‘new’ virus (antigenic shift) - susceptible population
- efficient person-person transmission
Describe avian flu
Many types of avian influenza, few strains affect humans (H5N1, H7N9)
Spreads through direct contact with infected birds
Occasional transmission via close human contact
High case fatality rate; H5N1 60%, H7N9 36%
Clinical features of influenza
Incubation period 2-4 days (range 1-7 days)
Abrupt fever up to 41C 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 commonly; nausea, vomiting, diarrhoea
Describe influenza like illness
WHO definition; fever (>38) and cough, onset within last 10 days
If requires hospitalisation defined as severe acute resp infection SARI)
Symptoms of swine flu
Typical; sudden fever, sudden cough
Others;
- Tiredness, chills
- Headache, sore throat, runny nose, sneezing
- Diarrhoea or stomach upset, app loss
- Aching muscles, limb or joint pain
Transmission of influenza
Airborne; person - person by large droplets >5microns
Contact; direct (person-person), indirect (prson - fomite - person)
Describe influenza virus shedding
First 4 days of illness (range 1-7 days)
Longer in young children and immunocompromised
Describe influenza virus sruvival
24-48 hours on non-porous surfaces
8-12hours on porous surfaces e.g. tissue
What are the risk factors for complicated influenza?
- Neurological, hepatic, renal, pulm and chronic cardiac disease
- Diabetes mellitus
- Severe immunosuppression
- Age over 65 years
- Pregnancy (incl up to two weeks post partum)
- Children <6months
- Morbid obesity (BMI≥40)
Common complications of influenza
- acute bronchitis
- secondary bacterial pneumonia (appears 4-5 days after start of flu)
Less common complications of influenza
Resp
- primary viral pneumonia
Cardiac
- myocarditis/pericarditis
CNS
- transverse myelitis/Guillain-Barre
- myositis and myoglobinuria
Describe encephalitis lethargia
Fever, headache
External opthalmoplegia
Lethargy
Sleep reversal
25% mortality
Postencephalitic parkinsonism
Serology +ve flu A
Diagnosis and investigations in influenza
Viral nose and throat swabs
CXR; pneumonitis/pnuemonia/ARDS
Blood culture
Pulse oximetry - SpO2 < 92% need ABG and oxygen
Resp rate
U and Es, FBC, CRP (CRP monitoring recovery of pneumonia)
Describe secondary bacterial pneumonia
Patients with flu symptoms and a fever >4days should have urgent CXR
Severity assessment with CURB65 score
Describe the CURB65 score
- Confusion
- Urea > 7mmol/l
- Resp rate >30
- BP (diastolic <60, systolic <90)
- > 65 years old
Describes risk of dearh in next 30days
Describe antiviral therapy
Use ASAP and within 48hrs symptom onset
In severe illness give no matter how long after onset
Oseltamivir orally and zanamivir inhaled or IV
Others include; peramivir, favipiravir, baloxavir
Describe oseltamivir
Oral antiviral
Dose; >13 years 75mg every 12 hours for 5 days
Common side effects;
- nausea, vomiting, abdo pain, diarrhoea
Less common SEs;
- headache, hallucinations, insomnia, rash
CAUTIONS
- renal dosing needed
Describe zanamivir
Inhales and/or IV
Available only as dry powder inhaler
Dose; >12 years, 10mg inhaled daily up to 10 days
Adverse side effects;
- occasionally bronchospasm
Describe antiviral therapy in pregnancy
Recommended due to adverse outcomes in this group
Oseltamivir still first line
When is a person non-infectious after influenza?
Immunocompetent adults
- 24hrs after last flu symptoms (fever and cough)
- or whenever anti-viral therapy completed
*whichever is longer
In immunocompromised adults and young children consider each case separately
Healthcare staff protection from influenza
Surgical face mask
Plastic apron
Gloves
Wash hands after any examination
Describe influenza vaccination
Seasonal flu vaccine
- prepared each year using most likely ciculating virus
- grown in chick embryos
- chemically inactivated and purified
- single 0.5 ml intramuscular injection
