Influenza (seasonal) Flashcards
What type of virus causes influenza?
Influenza virus. Type A, B, C.
Type A is subclassified further into H1N1 and H3N2. Type B has two lineages, while Type C is rare.
Major virus changes (antigenic shift) occur irregularly for type A viruses but can produce novel strains with epidemic/pandemic potential.
Minor virus changes (antigenic drift) occur frequently for influenza A - annual vaccine update.
What is the primary mode of transmission for influenza?
Respiratory droplets; direct contact; fomites; occasionally aerosol.
Animals, particularly wild aquatic birds, are suspected sources of new human subtypes.
Influenza A - natural reservoir = wild aquatic birds; natural hosts = pigs, horses, humans
What are the clinical features of influenza?
ARI – fever, cough, headache, myalgia, coryza, sore throat.
Complications may include pneumonia, myositis, and toxic shock syndrome.
Who is considered high risk for influenza complications?
≥ 65 years, comorbidities, immunocompromise, young children, pregnant.
These groups are more vulnerable to severe illness from influenza.
What is the definition of a confirmed influenza case?
Confirmed only (isolation/detection/seroconversion).
What diagnostic method is commonly used for influenza?
PCR (multiplex respiratory viral).
What is the incubation period for influenza?
Usually 2-3 days, range 1-7 days.
What is the infectious period for influenza?
24 hours prior to symptom onset, up to 7 days after onset.
Highest infectiousness occurs in the first 3-5 days.
Generally non-infections 24hr post fever, completed 72hrs antivirals or 5 days since resp sx onset.
Children can shed for 7-10 days.
What is the annual public health action for influenza?
Surveillance to monitor geographic spread and detect outbreaks.
This helps in health service planning and informs future vaccines.
What is the recommended prevention method for influenza?
Vaccination: annual vaccination on NIPS for specific groups.
Recommended for children 6m-5y, ≥65yo, specific medical conditions, Indigenous people, pregnant, and others in high-risk settings.
Also recommended for: homeless, HCW, RACF staff/residents, commercial poultry/pork industry workers, travellers during flu season.
Fill in the blank: The major virus changes in influenza A are called _______.
antigenic shift.
Fill in the blank: The minor virus changes in influenza A are called _______.
antigenic drift.
What resources are available for public health management of influenza?
SoNG, DH protocol, ARI outbreak guidelines.
https://www.health.gov.au/sites/default/files/2024-06/national-guideline-for-the-prevention-control-and-public-health-management-of-outbreaks-of-acute-respiratory-infection-in-residential-aged-care-homes.pdf
https://www.health.tas.gov.au/sites/default/files/2023-06/RACF%20ARI%20Toolkit%20v12%20FINAL%20%5Baccessible%5D.pdf
How are cases of influenza managed?
- Individual case F/U only for high-risk HCW (inc. RACF), outbreaks in sensitive settings, novel subtype/untypeable
- Clarify Sx, vaccination, travel, RFs
How are cases of influenza in a HCW managed?
- Clarify role
- High-risk settings
- Encourage notification of workplace
How are cases of novel/untypeable influenza managed?
- Ask about travel, animal contact during incubation/infectious period
- If no travel, ask about contact with returned travellers / other unwell contacts during incubation period
How should cases of influenza be managed clinically?
- Standard, contact, droplet precautions
- Hygiene education
- Antivirals (clinician discretion) - attenuates disease if given within 48hrs
How should contacts of influenza cases be managed?
No action except in high-risk settings or novel subtypes.
What should be done for contacts of an influenza case in high-risk settings?
Prophylaxis considered for contacts ideally within 48 hours.
Should influenza cases be excluded from school / work?
Yes.
How long should cases of influenza be excluded?
- ECEC - until well
- HCW high-risk setting - 5 days after sx onset or until well (whichever later)
- Residents of high-risk settings - isolate until non-infectious
- Others - encourage to stay home, avoid vulnerable settings, mask
What environmental management is required for influenza?
PPE, cleaning, waste Mx, signage (per outbreak guidance)
What is the definition of an influenza outbreak?
> = 2 cases in 72hrs in a residential facility.
How are influenza outbreaks managed?
Hospital - OMT with IPC team, R/V IPC practices.
School/childcare - consider letter reinforcing hygiene, control measures including vaccination.
When do influenza epidemics typically occur?
Winter. Varying severity.
Which group has the highest rates of influenza infection during epidemics?
Children.
0-9 years highest but also in pre-adolescence, teenagers.
What is the significance of influenza for society?
- Health: mortality, health system burden
- Economy: workplace absenteesim
When was the last influenza pandemic?
2009 H1N1.
Which were the worst influenza seasons in the last 2 decades?
2017 - 250k cases
2019 - 315k cases
2022 - 235k cases
2024 - 365k cases
High case numbers in recent years (‘22, ‘24) may be due to increased testing.
What is the purpose of influenza surveillance?
- Monitor geographic spread
- Detect outbreaks in sensitive settings
- Identify epidemics
- Health service planning
- Inform future vaccines
