influenza - optional Flashcards by Evie withington

when does seasonal influenza occur

during winter mths
dec-feb in northern hemisphere
jun-aug in southern hemisphere

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link between influenza and sun

more severe epidemics occur every 11yrs - same as increased sunspot activity
sun’s radiation may cause mutations leading to antigenic shifts in viral RNA

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influenza virus

RNA virus 
8 segment genome 
orthomyxoviridae family 
3 main groups (A, B, C)
IfA infects mammals and birds
IfB and IfC infects only humans

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surface proteins on influenza

haemagglutinin (H) - facilitates viral attachment and entry to host cell
18 different H antigens (H1-3 in humans)
Neuraminidase (N) - enables new virion to be released from host cell
11 different N antigens

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what is 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 and vaccine mismatch

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antigenic shift and new viral strains

abrupt major change in the virus
new H/N combinations
enables a flu strain to jump from one animal species to another
2 or more different strains of a virus combine to form a new subtype (new H/N combinations)
reassortment of the virus’s genes segments
new antigenic populations, population is unprotected and at risk, pandemics

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seasonal vs pandemic flu

seasonal: occurs every winter, affects 10-15% of population, unpleasant but not life-threatening
pandemic: occurs sporadically, affects ≥25% of the population, more serious and more complications

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antigenic shift and influenza

avian host
direct avian human transmission
swine host for both avian and human virus
new reassorted virus subtype is passed on to humans

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pandemic requirements

human pathogenicity
‘new’ virus - antigenic shift, susceptible population
efficient person-person transmission

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H1N1 pandemic infection and % affects

30% infection rate
of the 30% infected: 
0.1-0.35% fatality rate
2% hospital treatment 
15% complications 
82.7-82.9% mild symptoms

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age and mortality

higher in infants and young children
slight peak around 25-34y/o
mortality increases again in >50y/o

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impact of H1N1 pandemic

784 000 estimated cases of  ILI in england 
457 deaths in UK 
less severe illness than anticipated
25% global attack rate 
50% in school children 
majority of deaths in Africa

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how is avian flu spread

spreads through direct contact w/ infected birds (dead or alive)
occasional transmission via close human to human contact (staff, caregivers)
no known transmission by eating properly cooked food/eggs

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which strains of avian flu affect humans

only H5N1 and H7N9 strains affect humans

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fatality rates of avian flu

60% H5N1

36% H7N9

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clinical features of influenza

incubation period 2-4 days (up to 1-7)
abrupt fever up to 41C (commonly 38-40C) which lasts 3 days (1-5 days range)
plus 2 or more of: cough (sore through, rhinorrhoea), myalgia, headache, malaise
predominance of systemic symptoms
less common symptoms: N+V, diarrhoea

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influenza like illness (ILI)

defined by WHO for epidemiological reasons
fever (>38C) AND cough, onset within last 10 days

if requires hospitalisation = severe acute respiratory infection (SARI)

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transmission of influenza

airborne - person to person by large droplets (>5 microns)
direct contact - person to person
indirect contact - person to fomite to person

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viral shedding - influenza

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first 4 days of illness (range 1-7 days)

longer in young children and immunocompromised

viral survival - influenza

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24-48hrs on non-porous surfaces

8-12hrs on porous surface e.g. tissue

risk factors for complicated influenza

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neurological, hepatic, renal, pulmonary and chronic cardiac disease
DM 
severe immunosuppression 
>65y/o
pregnancy (incl up to 2wks post-partum)
<6mths old 
morbid obesity (BMI ≥40)

common respiratory complications of influenza

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acute bronchitis

2y bacterial pneumonia (~20%) - appears 4-5 days after start of flu

microbiology of 2y bacterial pneumonia

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1918: H. influenzae, S. pneumoniae, beta haemolytic strep
1957: S. aureus (>2/3)
1968: S. pneumoniae (48%), S. aureus (26%), H. influenzae (11%)
community MRSA uncommon in europe, concern in US

less common respiratory complications of influenza

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1y viral pneumonia - appears common in human cases of avian influenxa (H5N1)
rapid resp failure (within 48hrs)
mortality >40% within 7 days)

cardiac complications of influenza

less common myocarditis pericarditis

CNS complications of influenza

less common transverse myelitis/ Guillain Barre myositis and myoglobinuria

encephalitis lethargica

fever, headache external ophthalmoplegia lethargy sleep reversal 25% mortality postencephalitic Parkinsonism serology +ve flu IgA paralleled 1918-19 pandemic

diagnosis and investigations for influenza

viral nose and throat swabs/VTS (molecular detection/PCR) CXR - pneunonitis/pneumonia/ARDS blood culture pulse oximetry - SpO2 <92% need ABG and oxygen resp rate U+Es, FBC, CRP, (CRP monitoring recovery of pneumonia, should 1/2 in 4 days)

2y bacterial pneumonis invesigations

pts w/ flu like symptoms and a fever for >4 days should have an urgent CXR severity assessment w/ CURB65

CURB65

``` Confusion urea >7mmol/L RR >30 BP diastolic <60 OR systolic <90 >65y/o ```

CURB65 score risk of death in next 30 days

``` 0 - 0.6% 1 - 3.2% 2 - 13% 3 - 17% 4 - 41.5% 5 - 57% ```

2 examples of neuraminidase inhibitors commonly used

oseltamivir | zanamivir

antiviral therapy - when to use

use ASAP and within 48hrs of symptom onset but in complicated illness - should always be given no matter how long after onset of illness

oseltamivir (tamiflu) dose

oral >13y/o 75mg every 12hrs for 5 days

side effects of oseltamivir

common - N+V, abdo pain, diarrhoea less common - headache, hallucinations, insomnia, rash cautions - renal dosing needed

zanamivir (relenza) dose and adverse effects

inhaled or IV only available as dry powder inhaler dose - >12y/o, 10mg inhaled daily for up to 10 days adverse effects - rare, occasional bronchospasm

other antiviral therapy

peramivir favipiravir baloxavir marboxil amantadine and rimantadine not used due to resistance

peramivir (Alpivab)

neuroaminidase inhibitor licensed in USA and approved by european medicines agency IV infusion for uncomplicated influenza

favipiravir (Avigan)

viral RNA polymerase inhibitor licenced in Japan for 're-emerging influenza viruses' oral medication

baloxavir marboxil (Xofluza roche)

endonuclease inhibitor | one single dose

antiviral therapy in pregnancy

antivirals have been recommended due to the adverse outcomes in this group oseltamivir is 1st line no evidence of harm of either oseltamivir or zanamivir no malformation, maternal toxicity or embryotoxicity observed in animal studies

antiviral therapy in breastfeeding

only tiny amounts of oseltamivir in milk | current guidance is oral oseltamivir

when does an individual become non-infectious

immunocompetent adults - 24hrs after last flu symptoms (fever and cough), or when anti-viral therapy is completed (which ever is longer) immunosuppressed adults and young children - consider each case separately

protection for healthcare staff

for most pts w/ suspected of proven flu: surgical face mask, plastic apron, gloved wash hands after any examination pts who are receiving nebuliser, NIV etc w/ aerosolised virus - face fit FFP3 respirator mask

seasonal flu vaccine

prepared each year using viruses considered most likely to be circulating in the forthcoming winter CI in those w/ egg allergy as grown in chick embryo chemically inactivated and purified trivalent vaccine - 2 type A and 1 type B subtype viruses single 0.5ml IM injection only adverse affect is sore arm

new universal vaccine candidate

in phase 1 clinical trial haemagglutinin (HA) head constantly undergoes antigenic drift new vaccine candidate only contains HA stem - less likely to need updating each season could provide wider and longer-lasting immunity

why are healthcare workers vaccinated

protect themselves and their families reduce risk to 'at risk' pts reduced absence from work during influenza 'surge' activity

influenza - optional Flashcards

(47 cards)