influenza - optional Flashcards
when does seasonal influenza occur
during winter mths
dec-feb in northern hemisphere
jun-aug in southern hemisphere
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
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
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
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
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
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
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
pandemic requirements
human pathogenicity
‘new’ virus - antigenic shift, susceptible population
efficient person-person transmission
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
age and mortality
higher in infants and young children
slight peak around 25-34y/o
mortality increases again in >50y/o
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
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
which strains of avian flu affect humans
only H5N1 and H7N9 strains affect humans
fatality rates of avian flu
60% H5N1
36% H7N9
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
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)
transmission of influenza
airborne - person to person by large droplets (>5 microns)
direct contact - person to person
indirect contact - person to fomite to person
viral shedding - influenza
first 4 days of illness (range 1-7 days)
longer in young children and immunocompromised
viral survival - influenza
24-48hrs on non-porous surfaces
8-12hrs on porous surface e.g. tissue
risk factors for complicated influenza
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
acute bronchitis
2y bacterial pneumonia (~20%) - appears 4-5 days after start of flu
microbiology of 2y bacterial pneumonia
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
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
