Influenza

Question 1

Why does seasonal influenza occur in the winter months?

Answer 1

The sun’s radiation may cause mutations leading to antigenic shifts in viral RNA

? Theory that Vitamin D helps prevent viral infection ?

Question 2

Describe the influenza virus and the three main groups

Answer 2

RNA virus
Groups
A (infects birds + mammals)
B + C (B+C only infect humans)

Question 3

What surface antigens are there + how do they facilitate the virus?

Answer 3

H1-3 infect humans
(there are 18 different H antigens in total but infect other animals)

There are 11 different N antigens

Haemagglutinin (H)- facilitates viral attachment and entry to host cell

Neuraminidase (N)- enables new virion to be released from host cell

Question 4

What is antigenic drift?

Answer 4

Mechanism of genetic variation within the virus

(occurs over time, may change antigenic properties: eventually can cause inability of immune system to combat virus due to vaccine mismatch)

Question 5

What is antigenic shift?

Answer 5

Abrupt major change in the virus, resulting in new H/N combinations

(enables flu strain to jump between species)

Question 6

What can cause a pandemic?

Answer 6

New antigenic properties caused by antigenic shift causes the population to be unprotected

Question 7

Describe the features of pandemic flu

Answer 7

Occurs sporadically, affects 25% population, more serious, ‘new’ virus due to antigenic shift

Question 8

Describe the features of seasonal flu

Answer 8

Occurs every winter, affects 10-15% population, unpleasant but not life-threatening

Question 9

Describe features of Avian Flu

Answer 9

Many types
H5N1 + H7N9 infect humans
spread through direct contact with infected birds

high case fatality: 60% H5N1, 36% H7N9

Question 10

What are the clinical features of influenza?

Answer 10

Incubation period of 2-4 days
Abrupt fever (up to 41 C) which lasts 3 days
PLUS 2 or more of: cough, sore throat, rhinorrhoea, myalgia, headache, malaise
Systemic symptoms occur

Less common: nausea, vomiting, diarrhoea

Question 11

What is the definition of an Influenza Like Illness (ILI)

Answer 11

Fever > 38
cough
Onset within last 10 days

If it requires hospitlisatoin defined as severe acute respiratory infection (SARI)

Question 12

How is influenza transmitted?

Answer 12

Airborne (droplets)
Direct contact (person-person)
Indirect contact (person - object - person)

Question 13

What is the virus survival?

Answer 13

24-48 hours on non-porous surfaces

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

Question 14

Who are high risk groups for influenza?

Answer 14

Neurological, hepatic, renal, pulmonary and chronic cardiac disease
Diabetes mellitus
Severe immunosuppression
Age over 65 years
Pregnancy (including up to two weeks post partum)
Children under 6 months of age
Morbid obesity (BMI ≥40)

Question 15

What are common complications?

Answer 15

Respiratory complications: Acute bronchitis, secondary bacterial pneumonia

Cardiac: myocarditis, pericarditis

CNS: transverse myelitis, Guillain Barre, Myoglobinuria

Question 16

What are common pathogens causing influenza?

Answer 16

S. pneumoniae, Staph, aureus, H. influenzae

Question 17

What are the symptoms of Encephalitis Lethargica?

known as sleeping sickness

Answer 17

Fever
Headache
Inability to move eyes
Lethargy

Question 18

What is the prognosis of Encephalitis Lethargica?

Describe other features

Answer 18

25% mortality
Postencephalitic Parkinsonism ocurs
Serology positive for Influenza A

Question 19

What investigations are there for influenza?

Answer 19

Nose + throat swabs, PCR
CXR - pneumonitis, pneumonia, ARDS
Blood culture
Pulse oximetry
Resp rate
U+Es, FBC, CRP

Question 20

What is secondary bacterial pneumonia?

Answer 20

Patients with flu symptoms and a fever > 4 days should;d have urgent CXR

Question 21

How do you assess pneumonia severity?

Answer 21

CURB 65:
Confusion
Urea > 7 mmol/l
Resp rate > 30 breaths/ min
Blood pressure (diastolic < 60, systolic < 90)
> 65 years old

Question 22

What is the risk of death associated with CURB 65 score?

Answer 22

risk of death in next 30 days (0=0.6%, 1=3.2%, 2=13%, 3=17%, 4=41.5%, 5=57%)

Question 23

When should antiviral therapy be used?

Answer 23

ASAP and within 48 hours of symptom onset

Question 24

What antiviral drugs are there?

Answer 24

Oseltamivir (Tamiflu)- oral

Zanamivir (Relenza)- inhaled

Question 25

What are the side effects of the antiviral drugs?

Answer 25

Oseltamivir- nausea, vomiting, abdominal pain, diarrhoea
cautions: renal dosing needed

Zanamivir- rare, occasional bronchospasm

Question 26

What antiviral is recommended in pregnancy?

Answer 26

Oseltamivir
no maternal toxicity/ side effects

Plus only tiny amounts are present in breast milk

Question 27

When are individuals NON-infectious?

Answer 27

24 hours after last flu symptoms or when anti-viral therapy completed

immunocompromised + young: consider each case separately

Question 28

What do healthcare workers need to do when there are patients with flu?

Answer 28

Wear surgical face mask, plastic apron, gloves

Wash hands after any examination

Question 29

What is the purpose of flu vaccine?

Answer 29

to protect yourself + family
to reduced risk to ‘at risk’ patients
to reduce absence from work during influenza activity