Influenza

Question 1

When does seasonal influenza occur?

Answer 1

Winter months

Question 2

What is influenza virus?

Answer 2

RNA virus - 8 segment genome
Orthmoyxovirdae family
Three groups - A, B, and C
A infects mammals and bird but B + C is only humans

Question 3

What are the surface proteins of influenza virus?

Answer 3

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

Question 4

What is antigenic drift?

Answer 4

Mechanism of genetic variation within the virus
May change the antigenic properties and eventually immune system will not combat the virus as well
Causes worse epidemics and vaccine mismatch

Question 5

What is antigenic shift?

Answer 5

Abrupt major change in virus - new H/N combinations
Enables strain to jump from one animal species to another
Combine to form a new subtype
Reassortment of virus gene segments

Question 6

What is seasonal flu?

Answer 6

Occurs every winter
Affects 10-15% of population
Usually unpleasant but not life-threatening

Question 7

What is pandemic flu?

Answer 7

Occurs sporadically
Affects 25% + of the population
More serious and more complications

Question 8

What are the requirements for a pandemic?

Answer 8

Human pathogenicity
New virus - antigenic shift
Efficient person to person transmission

Question 9

Describe the Spanish flu

Answer 9

H1N1
Likely USA origin
33% of world population affected
50 million deaths

Question 10

Describe the Avian flu

Answer 10

H5N1 and H7N9 affect humans
Spreads by direct contact with infected birds, dead or alive
Occasionally by close human to human contact
Hugh case fatality rate

Question 11

What are the clinical features of influenza?

Answer 11

Incubation period is 2-4 days
Abrupt fever up to 41C which lasts 3 days
Plus 2 more of - cough, myalgia, headache or malaise
Predominance of systemic symptoms
Less common - N/V and diarrhoea

Question 12

What is the definition of influenza like illness?

Answer 12

Fever
Cough
Onset within the last 10 days
If hospitalised then SARI - severe acute respiratory infection

Question 13

What are the symptoms of swine flu?

Answer 13

Sudden fever and cough
Tiredness, chills, headache, sore throat, runny nose, diarrhoea or stomach upset, aching muscles and limb/ joint pain

Question 14

What is the transmission of influenza?

Answer 14

Airborne - person to person by large droplets
Contact - direct or indirect

Question 15

Describe virus shedding of influenza

Answer 15

Fist 4 days of illness
Longer in young children and immunocompromised

Question 16

Describe virus survival of influenza

Answer 16

24-48 hr on non-porous surfaces
8-12hrs on porous surface - tissue

Question 17

What are risk factors for complicated influenza?

Answer 17

Neurological, hepatic, renal, pulmonary and chronic cardiac disease
DM, serve immunosuppression, age over 65 years, pregnancy, children under 6 months of age and morbid obesity

Question 18

What are common respiratory complications of influenza?

Answer 18

Acute bronchitis
Secondary bacterial pneumonia - appears 4-5days after the start of flu

Question 19

What are some less common complications of infleunza?

Answer 19

Respiratory viral pneumonia - human cases of avian flu, rapid resp. failure within 24hrs, mortality is more than 40%
Myocarditis/ pericarditis
Transverse myelitis/ Guillain Barre
Myositis and myoglobinuria

Question 20

What are the symptoms of encephalitis lethargica?

Answer 20

Fever, headache, external ophthalmoplegia, lethargy, and sleep reversal

Question 21

Describe encephalitis lethargica

Answer 21

25% mortality
Post-encephalitic parkinsonism
Serology positive for flu A

Question 22

What is used for diagnosis and investigation of influenza?

Answer 22

Viral nose and throat swabs
Chest X-ray
Blood culture
Pulse oximetry
Resp. rate
U+Es, FBC, and CRP for monitoring recovery of pneumonia

Question 23

What investigation should be done if a patient has flu like symptoms and a fever for more than 4 days?

Answer 23

Urgent CXR

Question 24

What are neuraminidase inhibitors used?

Answer 24

Oseltamivir
Zanamivir

Question 25

Describe antiviral therapy for influenza

Answer 25

Use ASAP within 48hrs of symptom onset
Oseltamivir - oral
Zanamivir - inhaled and/or IV

Question 26

What are the adverse effects of Oseltamivir?

Answer 26

Common - N/V, abdominal pain and diarrhoea
Less common - headache, hallucinations, insomnia, and rash
Renal dosing needed

Question 27

What are the adverse effects of Zanamivir?

Answer 27

Rare - occasional bronchospasm

Question 28

What is complicated influenza?

Answer 28

Influenza requiring hospitalisation and/or with symptoms of lower respiratory tract infection, CNS involvement or exacerbating underlying medical condition

Question 29

What is some other antiviral therapies?

Answer 29

Peramivir - neuraminidase inhibitor and IV
Favipiravir - viral RNA polymerase inhibitor and oral
Baloxavir Marboxil - endonuclease inhibitor

Question 30

What is the guideline for antiviral therapy during pregnancy?

Answer 30

Oseltamivir remain first line
Breastfeeding - only tiny amounts of oseltamivir in milk and current guidance is oral oseltamivir

Question 31

When does an individual become non-infectious?

Answer 31

Immunocompetent - 24hrs after last flu symptoms or when antiviral therapy is completed
Immunocompromised and young children - consider each case separately

Question 32

What protection is needed for healthcare staff?

Answer 32

Surgical face mask, plastic apron and gloves
Wash hands
May need face fit if patient being nebulised

Question 33

Describe vaccination for influenza

Answer 33

Growth in chick embryos
Chemically inactivated and purified, trivalent vaccines - contains type A and B viruses