Influenza Flashcards
When does seasonal influenza occur?
Northern hemisphere = Dec-Feb
Southern Hemisphere = Jun-Aug
What relation doe s severe epidemics of influenza and increased sunspot activity have in common?
Occur every 11 years
What is the sun’s radiation role in influenza?
It is believed the sun’s radiation may cause mutations leading to antigenic shifts in viral RNA
What is vitamin D role in viral infections?
It is believed an increased level of Vitamin D helps to prevent viral infection
When did the Spanish flu pandemic occur?
1918-1919 = 20-100million deaths
When did the Asian flu pandemic occur?
1957-1958 = 1-1.5million deaths
When did the Hong Kong flu pandemic occur?
1968-1969 = 0.75-1 million deaths
When did the Swine flu pandemic occur?
2009-2010 = Approx 285,000 deaths
What type of virus is influenza?
RNA virus with an 8 segment genome
From what family is the influenza virus?
Influenza is an RNA virus from the Orthomyxoviridae family
What are the three main groups of influenza?
Type A = 1933
Type B = 1939
Type C = 1950
Which influenza infect mammals and birds?
Type A
Which influenza only infects humans?
Type B and Type C
What part of the influenza virus facilitates viral attachment and entry to host cell?
Haemagglutinin (H antigen)
How many different Haemagglutinin (H antigens) are there in influenza?
18 different Haemagglutin antigens (H1-3 in humans)
What part of the influenza virus enables new visions to be released from host cells?
Neuraminidase (N antigen)
How many different Neuraminidase (N antigens) are there in influenza?
11 different Neuraminidase antigens (N antigens)
What is Antigenic drift?
A mechanism of genetic variation within the virus cased by small on going point mutations in the genes coding for antibody binding sites
What is antigenic drift effect on the immune system?
Small mutations in the genes coding for antibody binding sites leads to the immune system not being able to combat the virus as well
What effect does antigenic drift have on vaccination?
Causes worse than normal epidemics & vaccine mismatch
A viruses with RNA or DNA genes more likely to undergo mutations?
RNA e.g. Influenza
Which strains does the influenza vaccine contain?
two A strains and one B strain - They are changed on a yearly basis dependant on the virus genetic drift
What allows one flu strain to jump from one animal species to another?
Antigenic shift
What is antigenic shift?
When 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”
What does antigenic shift often lead to?
Pandemics e.g. Bird flu/Swine Flu
The 2009/2010 influenza pandemic possessed which H/N antigens?
H1N1
Where did the 2009/2010 influenza pandemic originate?
In March 17th the first case as seen of the H1N1 influenza variant.
The first case in USA was identified March 28th
H1N1 was identified by the CDC April 14th
What is the main differences between seasonal flu and pandemic flu?
1) Seasonal = Every winter
Pandemic = Sporadic
2) Seasonal = 10-15% of the population
Pandemic = >25% of the population
3) Seasonal = Unpleasant but not life-threatening
Pandemic = More serious, more complications
What are the requirement of a pandemic?
1) Human pathogenicity
2) “New” virus (antigenic shift) - Susceptible population
3) Efficient person-person transmission
What are the characteristics of a pandemic?
“a new virus, a spike of cases outside the usual influenza season,
and a clear shift in the age distribution of illness and death”
What percentage of the UK population were infected with the H1N1 influenza virus in the 2009/2010 pandemic?
30% of the UK population
What percentage of the UK population infected with the H1N1 influenza virus in the 2009/2010 pandemic has mild symptoms?
82.7-82.9%
What percentage of the UK population infected with the H1N1 influenza virus in the 2009/2010 pandemic died?
0.1%-0.35% fatality rate (457 deaths)
What percentage of the UK population infected with the H1N1 influenza virus in the 2009/2010 pandemic required hospital treatment?
2%
What percentage of the UK population infected with the H1N1 influenza virus in the 2009/2010 pandemic had complications?
15%
What phenomenon did the 2009/2010 influenza pandemic follow?
A wave phenomenon
H/N antigens of the 1997 avian flu?
H5N1 - fatality rate of 60%
H/N antigens of the 2013 avian flu?
H7N9 - fatality rate of 36%
How is avian flu transmitted?
1) Directly from birds, dead or alive (Not from consumption)
2) Occasional transmission via close human to human contact (e.g. caregivers)
What are the current outbreaks of avian flu in China?
H7N9
What are the current outbreaks of avian flu in Egypt?
H5N1
What is the incubation period for influenza?
2-4days (Range 1-7days)
Clinical features of influenza?
1) Abrupt fever up to 41oC (commonly 38-40oC) which last for three days (Range 2-5 days)
2) Two or more of: Cough, Sore throat/rhinorrhoea, myalgia, headache, malaise
3) Systemic symptoms
4) Less commonly: Nausea, vomiting, diarrhoea
What are the characteristics of the fever in influenza?
Abrupt fever up to 41oC (commonly 38-40oC) which last for three days (Range 2-5 days)
What is the WHO (2011) definition for influenza?
- Fever >38oC; and
- Cough
Onset within the last 10 days
If influenza requires hospitalization what is it defined as?
Severe acute respiratory infection (SARI)
Common symptoms in swine flu?
1) Typical fever >38oC
2) Sudden cough
3) Malaise, chills
4) Headache, sore throat, rhinorhoea, sneezing
5) Diarrhoea or stomach upset, loss of appetite
6 )Aching muscles, numb or joint pain
How is Influenza transmitted?
Airborne = Person -> Person by large droplets >5 microns
Contact:
- Direct (Person –> Person)
- Indirect (Person –> fomite –> person)
Virus shedding in influenza?
- First 4 days of illness (Range from 1-7 days)
- Longer in young children and immunocompromised
Virus survival in influenza?
- 24-48 hours on non-porous surfaces
- 8-12 hours on porous surface e.g. tissue
How far does a sneeze spread?
3 feet
Who is at higher risk of complications in influenza?
1) Neurological hepatic, renal, pulmonary and chronic cardiac disease
2) Diabetes mellitus
3) Severe immunosuppression
4) >65 years old
5) Pregnancy - Including up to two weeks post partum
6) Children under 6 months
7) Morbid obesity (BMI >40)
Common respiratory complications of influenza?
- Acute bronchitis
- Secondary bacterial pneumonia (S pneumonia, S aureus, H influenza)
Less common complications of influenza?
1) Viral pneumonia:
- Common in avian influenza (H5N1)
- Rapid respiratory failure
- Mortality >40% within 7 days
2) Myocarditis/pericarditis
3) Transverse myelitis/Guillain-Barre
4) Myositis and Myoglobunuria
What was a big complication of the 1918 influenza pandemic?
Encephalitis lethargica
How does encephalitis lethargica present?
- Fever, headache
- External ophthalmoplegia
- Lethargy
- Sleep reversal
- 25% mortality
- Postencephalitis parkinsonism
How do we diagnose and investigate influenza?
1) Viral nose and throat swabs (PCR)
2) Chest radiograph - Pneumonitis/ARDS
3) Blood culture
4) Pulse oximetry - If SpO2 <92% need ABG and oxygen
5) Respiratory rate
6) U&E’s, FBC, CRP (Used to monitor recovery - Should halve in 4 days)
If patients have flu symptoms and a fever for longer than 4 days what should be done?
An urgent chest radiograph to rule out secondary bacterial pneumonia
What is used to to assess the severity of bacterial pneumonia?
CURB-65: C = Confusion U = Urea >7 mmol/L R = Resp rate >30 B = BP (diastolic <60 or systolic <90) 65 = Age >65 years
Risk of death in next 30days: 0 = 0.6% 1 = 3.2% 2 = 13% 3 = 17% 4 = 41.5% 5 = 57%
What is the risk of death in the next 30 days if a CURB-65 score is 0 in bacterial pneumonia?
0.6%
What is the risk of death in the next 30 days if a CURB-65 score is 1 in bacterial pneumonia?
3.2%
What is the risk of death in the next 30 days if a CURB-65 score is 3 in bacterial pneumonia?
17%
What is the risk of death in the next 30 days if a CURB-65 score is 4 in bacterial pneumonia?
41.5%
What is the risk of death in the next 30 days if a CURB-65 score is 5 in bacterial pneumonia?
57%
Treatments available for influenza virus?
Neuraminidase inhibitors:
- Oseltamivir
- Zanamivir
- Peramivir
Viral RNA polymerase inhibitor:
- Favipiravir
What dose is needed for Oseltamivir in influenza?
Oral - Over 13 years old = 75mg every 12 hours for 5 days
What dose is needed for Zanamivir in influenza
Inhaled - Over 12 years old = 10mg daily for up to 10 days
When should neuraminidase inhibitors be administered in flu?
ASAP, but within the first 48Hrs of symptom onset
In complicated disease should always be given
What are the adverse effects of Oseltamivir (Tamiflu)?
Common: Nausea, vomiting, abdominal pain, diarrhoea
Less common: Headache, hallucinations, insomnia, rash
Cautions - Renal dosing
What are the adverse effects of Zanamivir (Relenza)?
Rarely occasional bronchospasm
Which influenza strain has a higher risk of oseltamivir resistance? What should be used instead?
H1N1, Zanamivir
Which influenza strain has a lower risk of oseltamivir resistance?
H3N2
What is the first line therapy in complicated influenza unless H1N1?
1st line = Oseltamivir
2nd line = Zanamivir if poor clinical response or if H1N1 strain
In complicated influenza what is the 1st line therapy?
1st line = Oseltamivir
2nd line = Zanamivir if poor clinical response or if H1N1 strain
What is the therapy of choice in influenza within pregnancy?
1st line = Oseltamivir
2nd line = Zanamivir if poor clinical response or if H1N1 strain
What is the therapy of choice in influenza when breast feeding?
- Only tiny amounts of Oseltamivir in milk
- Current guidance is – Oral Oseltamivir
When does an individual become non-infectious after influenza?
Immunocompetent adult:
- 24hrs after last flu symptom
- Or when anti-viral therapy complete
Which ever is longer
Immunocompromised adults and young children:
- Case by case basis
How can healthcare staff protect themselves against influenza?
Proven or suspected “flu”:
- Surgical face mask
- Plastic apron
- Gloves
- Wash hands after examination
- Face-fit FFP3 respirator mask, eye protection and gown for though who are receiving a nebuliser
- Seasonal flu vaccination
Who cannot receive the seasonal flu vaccination?
Those who are allergic to eggs
How is the seasonal flu vaccination administered?
A single 0.5ml intramuscular injection
What are the complications of seasonal flu vaccine?
- Sore arm
- Rare = Tissue infection due to bad hygiene
Where is the flu vaccine grown?
Allantoic cavity of chick embryos
Why should healthcare workers receive the seasonal flu vaccination?
1) To protect themselves and their families
2) To reduce the risk to “at risk” patients
3) To reduce absence from work during influenza “surge” activity
