Influenza Flashcards
What do severe flu epidemics occur in accordance with?
•More severe epidemics of influenza occur every 11 years; same as increased ‘sunspot activity’
Why does the sun affect rates of flu?
- The sun’s radiation may cause mutations leading to “antigenic shifts’ in viral RNA.
- Theory that Vitamin D levels help to prevent viral infection
When was the spanish flu and how mamny people did it kill?
1918-1919
20-100 million deaths
What kind of virus is influenza?
RNA virus - 8 segment genome
Orthomyxoviridae family
What are the three main groups of influenza and what do they infect?
A - (mammals and birds)
B - humans
C - humans
What are the surface proteins for influenza?
Haemagglutinin
Neuraminidase
What is the function of haemagglutinin?
Facilitates viral attachment and entry to host cell
What is the funciton of neuraminidase
enables new virion to be released from host cell
What is antigenic drift?
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
Epidemics as a result are worse than normal and there is vaccination mismatch
What is 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
What are the key differences between seasonal flu and pandemic flu?
Seasonal Flu
occurs every winter, affects 10-15% of the population, usually unpleasant but not life threatening
Pandemic flu
Occurs sporadically
Affects 25% + of the population
More serious, more complications
What are the pandemic requirements?
Human pathogenicity
New virus (antigenic shift) - susceptible population
Efficienct person-person transmission
What are two strains of avian flu?
Few strains affect humans: H5N1 (since 1997),
H7N9 (since 2013)
How does avian flu spread?
Spreads through direct contact with infected birds, dead or alive
Occasional transmission via close human to human contact (staff, caregivers)
•No known transmission by eating properly cooked food/eggs etc
What is fatality rate?
•High case fatality rate: 60% (H5N1), 36% (H7N9)
What is the incubation period for influenza?
2-4 days (ranges from 1-7 days)
What are the clinical features of influenza?
- 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
What are methods of influenza transmission?
Airborne - person - person by large droplets (5 microns)
Contact - direct (person to person)
Indirect (person to fomite to person)
When does virus shedding occur?
The expulsion of offspring following successful reproduction during host cell infection
Occurs in the first 4 days of illness (range is 1-7 days)
Longer in young children and immunocompromised
What is the length of 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?
- a. Neurological, hepatic, renal, pulmonary and chronic cardiac disease
- b. Diabetes mellitus
- c. Severe immunosuppression
- d. Age over 65 years
- e. Pregnancy (including up to two weeks post partum)
- f. Children under 6 months of age
- g. Morbid obesity (BMI ≥40)
What are common complications from influenza?
Acute bronchitis
Secondary bacterial pneumonia (s.pneumoniae, staph aureus, H. influenzae) - 4/5 days after the start of flu
Less Common:
Primary viral pneumonia (H5N1) - appears common in human cases of avian influenza, rapid respiratory failure witin 48 hours, mortality is over 40% within 7 days
Cardiac - Myocarditis/pericarditis
CNS - transverse myelitis / guillain barre
Myositis and myoglobulinuria
Encephalitis lethargica - paralleled the 1918-1919 pandemic
What are the clinical features of encephalitis lethargica?
- Fever, headache
- External ophthalmoplegia
- Lethargy
- Sleep reversal
- 25 % mortality
- Postencephalitic Parkinsonism
- Serology +ve ’flu A
What are the relevant investigations 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)
When is an urgent CXR indicated?
•Patients with ‘flu symptoms and a fever for > 4days – should have an urgent CXR
(potential for secondary bacterial infection)
What is the severity assessment for pneumonia?
–Confusion
–Urea >7mmol/l
–Respiratory rate >30mm
–Blood Pressure (diastolic <60 or systolic <90)
–>65 years of age
What are two neuraminidase inhibitors?
Oseltamavir
Zanamavir
When should antiviral therapy commence?
ASAP - and within 48 hours of symptom onset
(•But, in complicated illness: “…should always be given, no matter how long after onset of illness…”)
What is the method of taking the medication for oseltamavir and zanamivir?
Oseltamivir - oral
Zanamivir - inhaled
What are common side effects for oseltamivir?
Nausea
Vomiting
Abdominal pain
Diarrhoea
What are the adverse effects of zanimivir?
Occasional bronchospasm
What is defined as complicated influenza?
Complicated influenza = influenza requiring hospitilisation admission and/or with symptoms and signs of lower respiratory tract infection (hypoxaemia, dyspnoea, lung infiltrate), central nervous system involvement and/or significant exacerbation of underlying medical condition
Requires hospital admission
LRTI
CNS involvement
Exacerbation of underlying condition
What are other antivrial therapies?
Peramivir (neuraminidase inhibitor)
Favipiravir (viral RNA polymerase inhibitor)
What is first line therapy for influenza in pregnancy and breast feeding?
Pregnancy - oseltamivir remains first line option - there is no evidence of harm of either oseltamivir or zanimivir
Breastfeeding - only tiny amounts of oseltamivir in milk
Oral oseltamivir is current guidance
When are individuals classed as being non-infectious?
- 24hrs after last ‘flu symptoms (fever & cough)
- Or when anti-viral therapy completed
Which ever is longer
Immunocompromised adults and young children - consider each case separately
What are the protection measures for healthcare staff
Surgical face mask
Plastic apron
Gloves
Wash hands after any examination
Face - fit respirator mask if there is a patient receiving nebulised with aerosolised virus (for aerosol generating procedures)
How is the seasonal flu vaccine made?
Prepared each year using viruses considered most likely to be circulating in the forthcoming winter
Grown in the allantoic cavity of chick embryos
Contraindicated in those with egg allergy
Chemically inactivated and purified
Contains 2 type A and 1 type B subtype viruses
Single 0.5 ml intramusclular injection
Why should healthcare workers have vacciation?
- To protect themselves and their families
- To reduce the risk to ‘at risk’ patients
- To reduce absence from work during influenza ‘surge’ activity
