Influenza
The disease
The Pathogen: RNA core surrounded by envelope containing 2 surface glycoproteins: Haemagglutinin (H), Neuraminidase (N)
Antigenic shift: major changes to antigenic structure, only occurs for influenza A
Antigenic drift: minor changes to antigenic (N, H) structure
Mode of transmission: droplets > direct and indirect contact > aerosols within confined spaces
Incubation p: 1 - 7 days, commonly 2-3 days
Infectious p: 24 hr pre symptoms - 7 days post onset of sx
Clinical presentation: fever, cough, fatigue, sore throat, myalgia, rigors or chilss
Complications: pneumonia, secondary bacterial pneumonia, ARDS
Routine Prevention
Persons at risk of severe disease: ATSI, elderly, young, immunocompromised, pregnancy, medical complications
Exclusion, vaccination esp HCWs, control of outbreaks in high risk settings
Surveillance systems:
Passive surveillance (e.g. CDPU) of lab dx
Syndromic surveillance: FluTracker
Sentinel: ASPREN (GPs), FLUCAN (Hospitals & complications)
Case definition: LAB ONLY. Positive i) respiratory tract specimen OR ii) serology
Respiratory tract specimen: isolation of influenza virus by culture, detection of virus by NAT, detection of virus antigen by fluorescent Ab
Serology: IgG seroconversion (4x rise in titre) or single high titre
ILI refers to cough AND fever
Historical pandemics: Spanish Flu (1918), Swine Flu 2009 (H1N1)
PH management
Contact Mx: none, unless high risk settings
PEP to be considered when patients or staff working in high risk settings have been exposed to a confirmed infectious case (e.g. neonatal, immunosuppressed wards)
High-risk settings
Residential care facilities
'A Practical Guide to assist in the Prevention and Management of Influenza Outbreaks in Residential Care Facilities in Aus'
Special schools
Consider anti-influenza medication
Boarding schools
Consider anti-influenza medication
Schools and childcare
Case Mx:
Infection control
Cohorting of patients
Droplet precautions: surgical mask, protective eyewear, disposable gloves, hand hygiene and respiratory/cough etiquette. If HCWs performing aerosol-generating procedures, should use N95 or P2 masks
Education
Cough etiquette and hand hygeine
If develop sx of severe influenza, should attend GP/hospital
Isolation: Stay home if unwell/ HCWs should remain home from work until 5 days after onset of sx, or until sx-free, whichever is longer. People with ILI who work with pigs or poultry should not attend work while infectious.
Antiviral medications may attenuate disease duration if given within 1st 48 hours of illness (oseltamivir)
Healthcare facilities
Case findings and Rx
Cohorting
Prophylaxis for high risk groups
Distribution of information letters
Epi studies to determine risks for infection
Aboriginal and TSI communities
Influenza A much more common than B (A >>B)
Dry swab vs. flocked swab: flocked swab superior as gathers more cells which means you can subtype virus
The vaccine
Components guided by surveillance of previous flu season in Northern Hemisphere. 2017: 2 x A and 2 x B strains. Determined by the Australian Influenza Vaccine Committee
If under 9 yr old: need 2 doses, 4 weeks apart in 1st year of vaccination
Catch-up vaccination for unvaccinated residents and visitors. ACF should have a vaccination policy where all residents are vaccinated.
Efficacy: 60%: greater in young, less in elderly. ~80% for preventing severe complications
Fluzone = high dose flu vaccine for those over 65 yr old. Fluzone contains 4 x the antigen, creates a stronger immune response.
Intended for older people who do not generate the same immune response post-flu vaccine. Contentious whether immune response leads to greater protection, prelim studies, including one in an ACF, promising. Approved in US (FDA) 2009. But one study found that the high dose vaccine did not outperform standard vaccine in one particular season.
Flu vaccine funded for adults >65 yo, pregnant women, ATSI 6 month to 5 yrs and >15 yrs, med conditions
H3N2 has been important in last 5 flu seasons, new variants emerge within a season
Pandemic: when a new strain emerges that the population is susceptible to.
Prevention
Preparation
Preparedness planning, ethical considerations, capacity building, Australian Health Management Plan for Pandemic Influenza, monitor emergence of diseases with pandemic potential
Response
Who to distribute vaccine to? Utilitarianism protect people who do the greatest good. Vulnerability assessment, but need to consider fairness
standown & Recovery
Vaccination, research, resource
PPE, vaccine, cohorting, exclusion, antiviral (treatment and prevention), containment at internatinoal borders, monitor distribution and use of antivirals, coordinate vaccination programs
Vaccine effectiveness determined by: uptake, mismatch btw vaccine strains and circulating strains, inad immune response by elderly/IC
Detection and communication
transition to seasonal arrangements, monitor for 2nd wave, monitor for antiviral resistance, communicate, evaluate
Characterise, communicate, confirm governance arragnements
INITIAL: Prepare and support health system needs, manage inital cases, characterise the disease in the australian context, provide info to HCWs about best practice
TARGETED:support and maintain quality care, ensure proportionate response, communicate to engage, emopower and build confidence in community, provide a coordinated and consistent approach