Influenza Flashcards
When does seasonal influenza occur?
Winter (dec-feb)
More severe epidemics every 11y
What vitamin is thought to help prevent viral infection?
Vit D
What kind of virus is influenza?
RNA virus
Of the orthomyoxviridae family
What are the main groups of influenza?
A
B
C
What are the surface proteins on the influenza virus?
Haemagglutinin (H) - facilitates viral attachment and entry into host cells (18 diff types)
Neuraminidase (N) - enables new virions to be released from host cells (11 diff types)
What is antigenic drift?
Genetic variation within virus
Causes epidemics
Due to small on-going point mutations in genes coding for Ab binding sites (minor changes in H and N) that does not alter the subtype
Leads to worse than normal epidemics & vaccine mismatch
What is antigenic shift?
Abrupt major chance in virus leading to new H and N combinations
Two different subtypes of virus enter same cell and there is mixing to form different combination
New antigenic properties –> population at risk and unprotected –> pandemics
What are the differences between pandemic and seasonal flu?
Pandemic occurs sporadically, affects 25% of pop or more and is more serious with more complications
Seasonal occurs every winter, affects 10-15% of population, and tends not to be lifethreatening
What are the requirements of a pandemic?
Human pathogenicity
New virus (antigenic shift)
Efficient person to person spread
What is the incubation period of the influenza virus?
2-4 days (range: 1-7)
What are the clinical features of influenza?
Abrupt fever (up to 41C) lasting 3 days (1-5) plus 2+ of: cough, myalgia, headache, malaise (sore throat, rhinorrhoea)
Less common symptoms: N/V, diarrhoea
What is the Who definition for an influenza like illness?
Fever (>38C) + cough
Onset within last 10 days
If influenza requires hospitalisation what is it called?
Severe, acute respiratory infection (SARI)
How is the influenza virus transmitted?
Airborne (large droplets >5microns), contact (direct - person to person or indirect (person-fomite-person)
What is viral shedding?
Repulsion and release of a virus after successful replication inside the host
When does viral shedding occur?
In the firsts 4 days of illness (range: 1-7 days)
But longer in children/immunocompromised
How long does the influenza virus survive on non-porous surfaces?
24-48h
How long does the influenza virus survive on porous surfaces?
8-12h
What are risk factors for complicated influenza?
Neurological, pulmonary, cardio, renal or hepatic disease DM Severe immunosuppression Age >65 Pregnancy (incl. 2 weeks post partum) Children <6m Morbid obesity (BMI >40)
What are the common complications of flu?
Acute bronchitis
Secondary bacterial pneumonia
When does secondary bacterial pneumonia appear?
4-5 days after flu
What microbes can cause secondary bacterial pneumonia?
S. pneumonia
Staph aureus
H. influenzae
What are less common complications of the flu?
Primary viral pneumonia
Myocarditis/pericarditis
Transverse myelitis/GB syndrome
Myositis/myoglobulinuria Encephalitis lethargica
With which flu are you more likely to get primary viral pneumonia?
Human avian influenza (H5N1)
Leads to rapid respiratory failure within 48h
Very high mortality
What is encephalitis lethargica?
Associated with serology +ve influenza A 1918 epidemic
Fever, headache, opthalmoplegia, lethargy, sleep reversal
May get post-encephalitic parkinsonism
What investigations should you do in suspected flu?
Viral nose & throat swab (molecular detection/PCR) CXR (?pneumonitis/pneumonia/ARDS) Blood culture Pulse oximetry if SpO2 <92% then do ABG U&E, FBC, CRP
How should CRP change in recovering pneumonia?
Half in 4 days
How do you investigate patients with suspected secondary bacterial pneumonia?
Patient with flu symptoms & fever >4 days should have urgent CXR
Measure severity with CURB65
What is CURB65?
Severity marker for pneumonia Gives risk of dying in next 30 days C- confusion U - urea >7mmol/L R- RR >30 BP - diastolic <60, systolic < 90 >65
How do you treat uncomplicated flu?
Symptomatic Rx - e.g. paracetamol & antivirals if HIGH RISK
How do you treat complicated influenza?
Admit to history & give antivirals
When should you start antivirals?
Within 48h of symptom onset
What antivirals do we use for flu?
Neuraminidase inhibitors -
Oseltamivir - 75mg every 12h x 5d (13y+)
Zanamivir - 10mg daily x 10d (12y+)
What are the ADRs of oseltamivir?
Common - abdominal pain, NV, diarrhoea
Uncommon - headache, hallucinations, insomnia, rash
Careful of renal dosing
What are the ADRs of zanamivir?
Rare - bronchospasm
What antiviral is best in uncomplicated flu with a dominant circulating strain that has low ostelamivir resistance (e.g. A (H3N2) or B)?
Oseltamivir PO
What antiviral is best in complicated flu with a dominant circulating strain that has low ostelamivir resistance (e.g. A (H3N2) or B)?
1st line: oseltamivir PO
2nd line: zanamivir INH/NEB/IV (if poor clinical response)
What antiviral is best in uncomplicated/complicated flu with a dominant circulating strain that high risk of ostelamivir resistance (e.g. A (H1N1))?
Zanamivir INH
May NEB/IV in complicated
What other antivirals can you use?
Peramivir - neuraminidase inhibitor
Favipiravir - RNA polymerase inhibitor
How do you Mx flu in pregnancy/breast feeding?
Antivirals - oseltamivir or zanamivir
Both are safe in pregnancy and breast feeding
When are people who have had flu considered non-infectious?
24h after last flu symptoms/when antiviral course complete
May be longer in immunocomp/kids
How can healthcare workers protect themselves from flu?
PPE (masks, plastic apron, gloves)
Handwashing
Wear face fit mask if patient receiving nebuliser
How are the seasonal flu vaccines prepared?
Consider most likely circulating viruses in forthcoming winter
Grown in allantoic cavity of chick embryo (CI in egg allergy)
Chemically inactivated and purified
What does the seasonal flu vaccine contain?
Trivalent - 2 type A and 1 type B subtype viruses
What is the dosage of the flu vaccine?
0.5ml IM
What are the adverse effects of flu vaccine?
Sore arm
When should people be vaccinated against flu?
From september to november
What flu vaccine is given to kids?
Intranasal live vaccine
Given at 2-3y then annual after than
if immunocompromised will need injectable inactivated vaccine
What are contraindications to the active intranasal flu vaccine?
Immunocompromised Age <2y Current febrile illness/blocked nose/rhinorrhoea Current wheeze/hx severe asthma Egg allergy Pregnancy/breast feeding Taking aspirin (risk of Reye's syndrome)
What are SEs of the intranasal active flu vaccine?
Blocked nose/rhinorrhoea
Headache
Anorexia
Who should be offered an annual flu vaccine?
Every >65 and those >6 months with:
- Chronic respiratory disease (incl. asthmatics on inhaled steroids)
- Chronic heart disease
- Chronic kidney disease
- Chronic liver disease
- Chronic neurological dsiease
- DM
- Immunosupression due to treatment or disease
- Asplenia/splenic dysfunction
- Pregnant women
- BMI >40
- Health and social care staff
- Those in residential homes
- Carers of the elderly/disabled
What kind of vaccine is the trivalent vaccine given to adults?
Inactived
What are side effects of the flu vaccine?
Fever and malaise
What are CIs to getting the inactive vaccine?
Egg allergy
How long does the flu vaccine take to work?
10-14 days
