Influenza

Question 1

When does influenza occur?

Answer 1

• Through the Winter months

* More severe episodes of influenza occur every 11 years; the same as increased sunspot activity

Question 2

Why might it be that the sun affects influenza?

Answer 2

• The sun’s radiation may cause mutations leading to “antigenic shifts’ in viral RNA
• Theory that Vitamin D levels help to prevent viral infection​

Question 3

Describe the influenza virus

Answer 3

• RNA virus. 8 segment genome ​
• Orthomyxoviridae family​
• Three main groups:​
○ A (1933) ​
○ B (1939) ​
○ C (1950)​
• Influenza A infects mammals and birds, Inluenza B & C only infects humans​

Question 4

What are the different surface proteins of influenzae?

Answer 4

• 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

Question 5

What is antigenic drift?

Answer 5

• Abrupt major change in the virus, resulting in new H/N combinations​
• The genetic change that enables a flu strain to jump from one animal species to another​
• The process by which 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​
• With new antigenic properties the population at risk is unprotected and this can lead to PANDEMICS

Question 6

What is the difference between seasonal flu and pandemic flu?

Answer 6

• seasonal flu
○ Occurs every winter​
○ Affects 10-15 % of the population​
○ Usually unpleasant but​ not life-threatening​
• Pandemic 
○ Occur sporadically​
○ Affects  25% + of the population​
○ More serious, more complications​

Question 7

What are the clinical features of Influenza?

Answer 7

• Incubation period 2-4 days (range 1-7 days)​
• Abrupt fever up to 41°C (commonly 38-40°C) which lasts 3 days (range 1-5 days)​
• Plus 2 or more of:
○ Cough
○ [sore throat, rhinorrhoea]
○ Myalgia
○ Headache
○ Malaise
• Predominance of systemic symptoms​
• Less common symptoms: Nausea, vomiting, diarrhoea​

Question 8

What is influenza like illness (ILI)?

Answer 8

• Fever (>38°C) and​
• Cough​
• Onset within the last 10 days​
• (if requires hospitalization defined as severe acute respiratory infection (SARI))​

Question 9

How is influenza transmitted?

Answer 9

• Airborne – person to person by large droplets >5 microns​
• Contact
○ Direct (person to person)​
○ Indirect (person to fomite to person)​

Question 10

When does virus shedding happen?

Answer 10

• First 4 days of illness (range 1-7 days)​

* Longer in young children & immunocompromised

Question 11

How long can Influenzae survive outside a host?

Answer 11

• 24-48 hours on non-porous surfaces​

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

Question 12

What are the risk factors for complications of influenza?

Answer 12

• 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 13

What are the common complications?

Answer 13

• Acute bronchitis
• Secondary bacterial pneumonia (appears 4-5 days after)
• Community MRSA uncommon in Europe but a concern in the USA

Question 14

What are the less common complications of influenza?

Answer 14

• RESPIRATORY:​
○ Primary viral pneumonia​
- appears common in human cases of avian influenza (H5N1)​
- rapid respiratory failure; within 48 hours​
- mortality >40%; within 7 days​