Influenza Flashcards
Which virus caused the influezna pandemics of Spanish Flu (1918-9) and Swine Flu (2009-10)?
Influenza A/H1N1
Which type of influenza virus can affect mammals and birds as well as humans?
Influenza A
B and C only affect humans
How are influenza viruses named?
HxNx, according to their surface proteins:
- Haemagglutinin (H) antigens, which facilitate viral attachement and entry to host cell
- Neuraminidase (N) antigens which enable release of new virion from host cell
What mechanism allows the influenza to vary genetically over time? What are the implications of this mechanism?
Antigenic drift
Causes worse than normal epidemics an vaccine mismatch
Is the reason for seasonal changes in the virus
What mechanism allows major changes in virus genetics? What are the implications of this mechanism?
Antigenic shift
Enables a flu strain to jump from one animal species to another
Leads to pandemics because the population is unprotected against the new antigens
E.g. Swine flu (combination of avian, human and pig virus)
Describe the mechanism of antigenic shift
Two or more different strains of a virus combine to form a new sub-type, resulting in new H/N combinations.
What proportion of the population are affected by seasonal flu each winter?
10 - 15%
What are the requirements for a viral infection to become a pandemic?
Virus must be pathogenic to humans
Must be a “new” virus (antigenic shift) so that the population is susceptible
There must be efficient person-to-person transmission
What is the wave phenomenon?
A phenomenon of infections that can develop during a pandemic. The disease infects one group of people first. Infections appear to decrease. And then, infections increase in a different part of the population, resulting in a second wave of infections.
What investigations and observations should be carried out in suspected cases of flu?
Viral nose and throat swabs CXR Blood culture (to rule out other causes such as bacterial sepsis) Pulse oximetry Respiratory rate U&Es, Creatinine FBC CRP
What method is used for assessing the severity of an influenza infection?
CURB-65
- Confusion
- Urea >7mmol/l
- Respiratory rate >30mm
- Blood Pressure (diastolic <60 or systolic <90)
- > 65 years of age
How is a CURB-65 score interpreted?
Indicates risk of death in the next 30 days:
0=0.6% 1=3.2% 2=13% 3=17% 4=41.5 5=57%
How does community-acquired influenza present?
- Abrupt fever up to 41oC (commonly 38-40oC) which lasts 3 days (range 1-5 days)
- Plus 2 or more of: Cough, sore throat, rhinorrhoea, myalgia, headache, malaise.
- Predominance of systemic symptoms (other respiratory illnesses e.g. cold do not cause pronounced systemic symptoms)
- Less common symptoms: Nausea, vomiting, diarrhoea
What is the incubation period of influenza?
Usually 2 - 4 days but can range from 1 - 7 days
Give three common respiratory complications of influenza
Acute bronchitis
Secondary bacterial pneumonia (20%)
Community MRSA (USA)
