Viva - Influenza Flashcards
Describe the flu virus
Influenza is an orthomyxovirus
Consists of 8 strands of RNA protected by an M1 matrix protein.
An envelope derived from the host cell envelops this, two types of glycoprotein are embedded
H and N (as in the H1N1) - these determine whether it is A or B and the subtype eg/ H1N1
These also act as the target of antiviral agents
What does the H1N1 nomenclature mean
These are the glycoproteins embedded within the envelope:
H - Haemagglutinin - 16 different kinds.
N - Neuraminidase - 9 different kinds
H: facilitates binding of virus to Host respiratory epithelial cells
N: allows release of new viral particles from infected cells
What is antigenic drift
Describes small genetic changes that happen continuously over time as the virus replicates and produces viruses closely related to one another.
They share the shame antigenic properties.
An immune system with prior exposure to one that is similar will recognise it and respond
What is antigenic shift
An abrupt major change that results in a new Haemagglutinin and/or Neuroaminidase producing a new influenza A subtype.
Have little or no immunity against the new subtype…pandemic results.
Also occurs when H/N combination emerges from animal popuation that is so different from the same subtype in humans that most people do not have immunity to it.
Which flu can undergo antigenic shifts and drifts
Influenza A
Undergoes periodic changes in antigenic characteristics of its glycoproteins.
B has a less propensity for this, and actually only drift in the Haemagluttinin has been described in B.
Incubation period of influenza
1.5 - 3 days
Presentation of influenze
incubation 1.5 - 3 days
Mild: afebrile upper resp tract infection all the way to fulminant viral pneumonia.
Non-specifically as self limiting in children and adults
Fever malaise, myalgia, arthralgia, headache, cough, upper resp symptoms,
GI commonly abdo pain, D&V
More seriously:
Dypnoea, heamoptysis, puruluent sputum, recurrent lower tract symtpoms, dehydration, altered mentation,
Suggest progression to severe disease or complications
Complications of influenza
Viral pneumonitis with severe hypoxaemia and ARDS requiring ITU.
Intubation often needed in first 24 hours
CXR - diffuse interstitial and alveolar shadowing
CT - ground glass opacities, air bronchograms and alveloar consolidation
Shock and AKI
CURB-65 will not help here.
2) Bacterial superadded infection
1/5th of patients.
Usually s.aureus (MRSA), st. pneumoniae, St pyogenes
3) Decompensation of pre-existing illness
4) less common: neuro:
Altered mental state, seizures, encephalitis, post infectious encephalopathy
5) viral myocarditis - unusual but poor prognosis
Who are the high risk patients
1) Extreme age <5 (especially <2 and high hospitalisation in <1)
or >65 (in 2009, they had highest fatality but lowest rate of infection
2) Pregnant - atypical presentation, increased hospital risk, highest at 3rd trimester.
Risk of severe illness, miscarraige, pre-term labour, fetal distress
3) Chronic diseases, ashthma, COPD, CF,
CCF, CAD
Dialysis, cirrhotic liver disease DM
4) morbid obesity
5) immunocomprimised
Chemo/steroids
HIV
Transplant
Malnutrition
Diagnosis of influenza
Suggestive clinical picture
Nasopharyngeal swab/aspirates for reatime RT-PCR for viral RNA
BAL better.
Management of influenza - outline principles
1) Manage with ABCDE….
2) Specific organ support
A) Strict infection control
B - Antiviral therapy
C -Antibiotic therapy if superadded infection
D - General principles - VTE, enteral feeding, acid suppression, VAP bundles
E - PEP
What are the infecion control principles
Isolate in side room - at least 24 hours after resolution of fever, or 7 days after onset of illness (whichever is longer)
Barrier nurse, strict hand hygeine
AGPs needs full protective kit and PPE, FFP3 or respirators, use as few staff as possible
More:
Year flu vaccines
PPE and hand hygeins, gloves, gown (or apron) goggles, surgical mask
Circuits: Disposable circuit, bacterial filter
Closed circuit suction uses respirators if breaking circuit
NIV - only turn on when mask is in situ
Avoid humidification
Negative pressure preferable
Negative pressure rooms (allow air in but not out the room) used with airborne infectious diseases, flu, TB
Positive pressure - isolate immunocomprimised
When to initiate antivirals
in 2009:
Suspected/confirmed H1N1 who were sevrely ill or high risk or had complications
Treatment with Neuraminidase inhibitors reduced severity and mortality
Resitstant to amantidine
Evidence for steroids
None
When to give PEP
Close contact with confirmed or suspected case
HCPs
Increased risk of developing complications
