Influenza Flashcards
In what months does seasonal influenza occur?
Seasonal influenza occurs during winter months:
- Dec to Feb in Northern hemisphere
- Jun to Aug in Southern hemisphere
Why do epidemics of influenza occur every roughly 11 years?
Epidemics occur every 11 years which is thought to be linked to sunspot activity that causing antigenic shifts in viral RNA (mutation)
What kind of virus is influenza?
Is an RNA virus with 8 segment genome:
- Orthomyxoviridae family
- Three main groups
- Influenza A
- Mammals and birds
- Influenza B
- Only humans
- Influenza C
- Only humans
- Influenza A
What are the 3 main groups of influenza and what animals do they infect?
- Influenza A
- Mammals and birds
- Influenza B
- Only humans
- Influenza C
- Only humans
From what family of viruses is influenza from?
- Orthomyxoviridae family
What are the surface proteins of influenza?
- 18 different H antigens (H1-3 in humans)
- Haemagglutinin (H)
- Facilitates viral attachment and entry to host cell
- Haemagglutinin (H)
- 11 different N antigens
- Neuraminidase (N)
- Enables new virion to be released from host cell
- Neuraminidase (N)
What is the function of haemagglutinin?
- Facilitates viral attachment and entry to host cell
What is the function of neuraminidase?
- Enables new virion to be released from host cell
What is antigenic drift?
- Is mechanism of genetic variation within virus
- Occurs continuously over time, small on-going point mutations in genes coding for antibody binding sites
- May change the antigenic properties and eventually immune system will not combat virus well
- Causes worse than normal epidemics and vaccine mismatch
What are consequences of antigenic drift?
- Causes worse than normal epidemics and vaccine mismatch
What is antigenic shift?
- Is abrupt major changes in virus resulting in new H/N combinations
- Enables flu strain to jump from one animal species to another
- Process by which two or more different strains of virus combine to form new subtype, creating new H/N combincations (reassortment)
- With new antigenic properties can lead to pandemics due to population being unprotected
What are consequences of antigenic shift?
- With new antigenic properties can lead to pandemics due to population being unprotected
Compare and contrast seasonal flu and pandemic flu in terms of when it occurs, incidence and severity?
What are pandemic requirements?
- Human pathogenicity
- ‘New’ virus (antigenic shift), creating susceptible population
- Efficient person-person transmission
How can you describe the incidence of pandemics over the year?
Incidence of pandemics is still a wave due to being worse in winter
What is avian flu?
Refers to disease caused by infection with avian (bird) influenza
Only a few strains affect humans, spreads through direct contact with infected birds that are either dead or alive
What is the clinical presentation of influenza?
- Abrupt fever up to 41oC which lasts 3 days (range 1-5 days)
- Plus 2 or more of
- Cough, myalgia, headache, malaise
- Predominance of systemic symptoms
- Less common symptoms
- Nausea, vomiting, diarrhoea
What is the WHO definition of an influenza like illness (ILI)?
- Fever and
- Cough
- Onset within last 10 days
- If requires hospitalisation is defined as severe acute respiratory infection (SARI)
What does ILI stand for?
Influenza like illness
What does SARI stand for?
Severe acute respiratory infection
What are the ways influenza can be transmitted?
- Airborne
- Person to person by large droplets (>5 microns)
- Contact
- Direct (person to person)
- Indirect (person to fomite to person)
What is virus shedding?
- Refers to expulsion and release of virus following successful reproduction during host-cell infection
When does virus shedding of influenza occur?
Virus shedding occurs in first 4 days of illness (range is 1 to 7 days):
- Refers to expulsion and release of virus following successful reproduction during host-cell infection
- Longer in young children and immunocompromised
What is the virus survival time of influenza on non-porous and porous surfaces?
- 24-48 hours on non-porous surfaces
- 8-12 hours on porous surface such as tissue
What are some risk factors (high risk groups) 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 some complications of influenza?
- Common
- Acute bronchitis
- Secondary bacterial pneumonia
- Less common
- Primary viral pneumonia
- Myocarditis/pericarditis
- Transverse myelitis/Guillain-Barre
- Myositis and myoglobinuria
Severity assessment of secondary bacterial pneumonia from influenza uses what score to asses severity?
CURB65 score
Describe the CURB65 score?
- Confusion
- Urea >7mmol/l
- Respiratory rate >30mm
- Blood Pressure (diastolic <60 or systolic <90)
- >65 years of age
Risk of death in next 30 days increases as CURB65 score increases
When should patients with influenza get an urgent chest x-ray?
Patients with “flu symptoms and fever for >4 days” should have an urgent chest x-ray
How is influenza diagnosed?
- Viral nose and throat swabs (molecular detection/PCR flocked swabs)
What investigations are done for influenza?
- Chest x-ray
- Pneumonitis/pneumonia/ARDSS
- Blood culture
- Pulse oximetry
- Respiratory rate
- U&Es, FBC, CRP
When should antivrial therapy be used for influenza?
Use ASAP and within 48 hours of symptoms onset
What are the different kinds of antiviral therapy for influenza?
- Oseltamivir
- Oral administration
- Dose if over 13 years is 75mg every 12 hours for 5 days
- Adverse effects
- Common – Nausea, vomiting, abdominal pain, diarrhoea
- Less Common – Headache, hallucinations, insomnia and rash
- Zanamivir
- Inhaled or IV administration
- Dose if over 12 years is 10mg inhaled daily for up to 10 days
- Adverse effects
- Rare - occasional bronchospasms
Describe the lines of treatment for influenza?
1st line - oseltamivir
2nd line - zanamivir
Other than oseltamivir and zanamivir, what are some other antiviral therapies?
- Peramivir
- Neuroaminidase inhibitor
- IV infusion for uncomplicated influenza
- Favipiravir
- Viral RNA polymerase inhibitor
- Oral
- Baloxavir marboxil
- Endonuclease inhibitor
- One single dose
What is the pregnancy guidelines for treatment of influenza?
- Antivirals are recommended
- Oseltamivir remains first line option
What is the breastfeeding guidance for influenza treatment?
- Current guidance is oral oseltamivir
When does somone with influenza become non-infectious?
Immunocompetent adult:
- 24 hours after last flu symptoms (fever and cough)
- Or when anti-viral therapy completed
- Whichever is longer
Immunocompromised adults and young children:
- Consider each case separately
What protection against influenza can healthcare staff use?
- Surgical face mask
- Plastic apron
- Gloves
- Wash hands after any examination
What kind of administration is the seasonal influenza vaccine?
Intramuscular injection
How is the season influenza vaccine prepared?
- Prepared from viruses considered to most likely be circulating in forthcoming Winter
- Grown in chick embryos
- Chemically inactivated and purified, trivalent vaccines
- Containing 2 type A and 1 type B subtype viruses
So cannot be used with egg allergy
How many types of influenza does the seasonal vaccine contain?
- Containing 2 type A and 1 type B subtype viruses
Why should healthcare workers be vaccinated against influenza?
- To protect themselves and families
- Reduce the risk to at risk patients
- Reduce absence from work during influenza surge activity
