Influenza

Question 1

When do seasonal influenza epidemics peak in the northern hemisphere?

Answer 1

During the winter

Question 2

Describe the influenza virus

Answer 2

RNA virus part of the Orthomyxoviridae family

Three main groups: A, B and C

Question 3

How is influenza spread

Answer 3

Rapid person-person spread by aerosolized droplets and contact

Question 4

Influenza A is subdivided according to what?

Answer 4

Combinations of virus surface proteins

e.g A(H1N1), A(H3N2)

Question 5

What is antigenic drift?

Answer 5

A mechanism of genetic variation within the virus whereby it changes continually over time through small point mutations

May change the antigenic properties (ways in which the immune system normally detects it) and eventually the immune system will not combat the virus as well

Question 6

What can happen as a result of antigenic drift?

Answer 6

Worse than normal epidemics

Vaccine mismatch

Question 7

What is antigenic shift?

Answer 7

Abrupt major change in the virus, resulting in new H/N combinations. It is the process by which 2 or more different strains of a virus, or strains of 2 or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains.

The genetic change that enables a flu strain to jump from one animal species to another

With new antigenic properties the population at risk is unprotected and this can lead to PANDEMICS

Question 8

What is Haemagglutinin (H) responsible for?

Answer 8

Surface enzyme that facilitates viral attachment and entry to host cell

Question 9

What is Neuraminidase (N) responsible for?

Answer 9

Surface enzyme that enables new virion to be released from host cell

Question 10

The human influenza flu (swine flu) pandemic in 2009 was caused by which subtype of influenza?

Answer 10

Influenza A (H1N1)

Question 11

What was the deadly influenza pandemic that occurred in 1918?

Answer 11

Spanish flu

Question 12

How is a pandemic influenza different to the seasonal flu that happens every year during winter?

Answer 12

Pandemics occur about three times each century and can arise at any time of year.

Ordinary flu affects about 10-15% of the population whereas a pandemic has affected 25% or more

A pandemic influenza is usually a more serious infection for everyone with more complications.

Question 13

What does a pandemic require to happen?

Answer 13

Human pathogenicity i.e. a virus, bacterium, prion, or fungus that causes disease in humans

‘New’ virus (antigenic shift) - susceptible population

Efficient person-person transmission

Question 14

Which strains of avian influenza affect humans?

Answer 14

H5N1

H7N9

Question 15

How does avian flu spread?

Answer 15

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

Question 16

What are the clinical features of influenza?

Note incubation period and symptoms

Answer 16

Incubation period 2-4 days (range 1-7 days)

Abrupt fever up to 41 degrees lasting 3 days

Plus 2 or more of: cough, sore throat, myalgia, headache, malaise

Question 17

What is influenza like illness (ILI), also known as flu-like symptoms?

Answer 17

A diagnosis of possible influenza or other illness causing these common symptoms:

Fever (>38°C) AND cough

Onset within the last 10 days

Question 18

How can influenza be transmitted?

Answer 18

Airborne: person-person by large droplets

Contact - direct (person-person) or indirect (person-object-person)

Question 19

Who is at risk of developing a complicated case of influenza?

Answer 19

Neurological, hepatic, renal, pulmonary and chronic cardiac disease

DM

Severe immunosuppression

Age > 65 years

Pregnancy (including up to two weeks post partum)

Children under 6 months of age

Morbid obesity (BMI ≥40)

Question 20

Common respiratory complications associated with influenza (2) ie what do patients commonly develop after having influenza infection

Answer 20

Acute Bronchitis

Secondary bacterial pneumonia

Question 21

Less common general complications associated with influenza

Answer 21

Primary viral pneumonia

Rapid respiratory failure

Myocarditis/pericarditis

CNS: Transverse myelitis/Guillain-Barre
or Myositis & Myoglobinuria

Question 22

Diagnosis and investigations for influenza

Answer 22

Viral nose and throat swabs/VTS (Molecular detection /PCR; using flocked swabs)

CXR – 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)

Question 23

Which scoring tool is used to assess the severity assessment for pneumonia?

Answer 23

CURB 65

Confusion
Urea >7mmol/L
Resp rate >30
BP - diastolic <60 or systolic <90

> 65 years of age

5/5 = 57% risk of death in next 30 days

Question 24

What are neuraminidase inhibitors?

Answer 24

A class of anti-viral drug.

They block the neuraminidase enzyme on the surface of viruses. This prevents its reproduction by budding from the host cell

Question 25

When should anti-virals be administered?

Answer 25

ASAP and within 48 hours of symptom onset.

In complicated illness, give them regardless of timing.

Question 26

Name 2 common anti-viral drugs

Answer 26

1st line Oseltamivir (oral)

2nd line - Zanamivir (inhaled or I.V)

Question 27

What is considered ‘complicated influenza’?

Answer 27

Influenza requiring hospital admission and/or with symptoms and signs of LRTI, CNS involvement and/or a significant exacerbation of an underlying medical condition

Question 28

Current guidelines on antiviral therapy during pregnancy?

Answer 28

Antivirals have been recommended due to the adverse outcomes in this group

Oseltamivir remains first line option

Question 29

When does an individual become non-infectious?

Answer 29

In immunocompetent adults - 24 hours after last flu symptoms or when anti-viral treatment is complete

In immunocompromised adults + young children - consider each case seperately