Influenza, Pandemics & Other Respiratory Infections Flashcards
Where did influenza come from
Zoonotic
Genera of influenza & which are more common in humans
A, B, C
A&B main human pathogens
Subdivision of influenza A
Subdivided by 2 surface antigens:
- Haemagglutanin (15 subtypes)
- Neuraminidase (9 subtypes)
All 15H and 9N have been detected in birds.
E.g. H1N1
Why can influenza change/mutate
Can get gene reassortment in infections
Gene swapping can occur during co-infection with human and avian flu virus
No proof reading mechanism so prone to mutation
What causes seasonal flu epidemics?
Minor antigenic variation = antigenic drift
What causes flu pandemics
Gene re-assortment & major antigenic variation = antigenic shift
Where does gene re-assortment often occur for flu
Animal (pig) reservoir- get bird virus and human virus at same time –> viruses combine –> new virus adapted to spread rapidly in humans
Or virus straight from bird –> human (human reservoir)
How do humans promote zoonotic infections
Humans in close proximity to animals - wet/live markets etc.
Intensive farming: bringing lots of animals in close proximity to each other
Farm parks/zoos
Influenza A
Can infect pigs, cats, horses, birds, sea mammals, humans
Causes severe & extensive outbreaks and pandemics
Influenza B
Tends to cause sporadic outbreaks (schools, care homes, garrisons) that are less severe
More often seen in children
Like A - prone to mutation
Influenza C
Relatively minor disease
Mild symptoms or asymptomatic
Influenza transmission
Mainly via aerosols generated by coughs & sneezes.
Possible via hand-hand contact, other personal contact & fomites
Influenza infection symptoms & complications
Upper +/- lower respiratory tract symptoms + fever, headache, myalgia, weakness
Complications: include bacterial pneumonia, life threatening
People with higher risk of flu mortality
Underlying medical conditions
chronic cardiac & pulmonary diseases
old age
chronic metabolic diseases
chronic renal disease
immunosuppressed
Influenza treatment
Supportive care (oxygen, hydration, nutrition, maintain homeostasis, prevent/treat secondary infections)
Antivirals: reduce risk of transmission, reduce severity and duration of symptoms (only really see a difference at a population level)
Seasonal flu
Antigenic drift every year - so can infect people who were immune to last years varient.
Usually peaks December - March (northern hemisphere)
Southern hemisphere - analyses their strains to make predictions for vaccines
Avian Influenza - about
Avian pathogen but can transmit to humans.
Usually mild in birds but can mutate to 100% mortality form.
~50% death rate in humans
HIgh risk of becoming pandemic
How to control avian influenza
Cull affected birds
Biosecurity & quarantine (e.g. 5-10km around a farm)
Disinfect farms
Control poultry movement
Vaccinate workers with seasonal flu jab
Antivirals for poultry workers
PPE
Try to reduce chance of coinfection
What is the number 1 risk to UK
Pandemic flu
Reasons for more pandemics
More travel
More people
Intensive farming (more animal contact with humans & factory farming)
Why are we better equipped to deal with pandemics
- Better nutrition, overall healthier population
- Better supportive care
- Vaccination
- Antivirals
Infection control responses to pandemics
Hand hygiene, cough etiquette
PPE
Surgical masks (for non aerosol generating procedures)
Segregation of patients
Reduce social contact
Flu surgeries (separate potentially infected patients)
Environmental cleaning
Ventillation
Population wide interventions for pandemics
Travel restrictions (slow transmission to buy time)
Restrictions of public gatherings
School closure (effectiveness depends on where infection is spreading)
Voluntary home isolation of cases
Voluntary quarantine of contacts
Screening on entry to UK
SARS CoV Info
2002
Animal origin/reservoir = bats
Intermediate hosts = civet cats
Incubation 2-7 days.
Case Fatality Rate: <24y: <1%. >50% in over 65s
No vaccine or specific treatment
Superspreading
SARS S&S
Fever, cough, SOB, myalgia, diarrhoea
CXR shows pneumonia or respiratory distress syndrome
MERS CoV
2012
Presents like SARS with severe acute respiratory disease
Bat origin. Intermediate host: camels
Superspreading
Covid-19
Swiss cheese method of response (detect, test, trace, isolate, support)
Will become endemic but hasn’t yet.
Virus survives longer in higher humidity
Pandemic response
Local, national & global surveillance
Epidemiological surveillance
Wastewater surveillance
Research (reinfections, durability of immunity, long covid, population behaviour)
Rapid evidence reviews
Vaccine efficacy studies
Challenges & issues in Covid
Challenges:
misinformation & disinformation, covid deniers, antivax
Issues:
- health literacy
- epidemiological literacy (especially in politicians)
- risk perception
Pneumonia causes
Respiratory viruses, bacterial and fungal
Typical pneumonias: Strep pneumonia, klebsiella, haemophilus influenza, staph a, group A strep, moraxella, pseudomonus
Atypical pneumonias:
mycoplasma, legionella pneumophilia (Legionnaires), chlamydia psitacci (bird exposure), aspergillus (mouldy hay)
Classification of pneumonias
CAP (acute infection of lung tissue in a patient who has acquired it from the community or within 48 hours of the hospital admission)
HAP (acute infection of lung tissue in a non-intubated patient that develops after 48 hours of hospitalization)
HCAP (Healthcare associated): acute infection of lung tissue acquired from healthcare facilities such as nursing homes, dialysis centers, outpatient clinics, or a patient with a history of hospitalization within the past three months.
VAP (Ventilator associated): A type of nosocomial infection of lung tissue that usually develops 48 hours or longer after intubation for mechanical ventilation
Pneumonia risk
Top 10 cause of death USA
Mortality from uncomplicated disease ~3%
Mortality from bacteraemic pneumonia 25%
1 million deaths globally pa in <5s
Risky even for young adults
5-10% pts admitted with CAP need intensive care
- Most common dangerous organisms = pneumoccocus (strep pneumonia) & legionella
S. pneumonia (pneumococcus)
Common secondary infection
Lots of different serotypes
Causes meningitis, sepsis, invasive pneumococcal disease (severe pneumonia)
Also causes >50% of otitis media in children & milder pneumonia and bronchitis
Most common secondary bacterial infection of influenza
Why do people get pneumonia
- defect in host immune defenses
- particularly virulent bacteria
- overwhelming inoculum
- Gains entry to lower respiratory tract: inhalation of aerosolised material or aspiration of upper respiratory tract resident flora
Risk factors for pneumococcal disease
Reduced consciousness
Serious underlying disease
Factors impairing clearance of pulmonary pathogens (CF etc.)
Hypoxaemia
Acidosis
Alcohol
Toxic inhalations
pulmonary oedema
uraemia
malnutrition
steroids
immunosuppressives
viral infection
mechanical obstruction
Importance of pneumonia prevention
High risk to elderly
High rate of CAP
Increasing resistance and multi resistant strains
Pneumonia prevention strategies
Infection control in hospitals
Vaccination programmes (e.g. PCV13, PPV23)
Stop people getting things that make them susceptible – give flu vaccine and pneumonia vaccine to elderly etc.
Reduce occupational hazards (dust exposure –> wear masks etc.)
Nutrition
Respiratory Syncytial Virus (RSV) about
Common cause of winter coughs & colds
Major cause of bronchiolitis in infants
Transmission: large droplets & secretions & fomites
Survives on hard surfaces: 4-7 hours
Incubation period: 3-5 days
RSV epidemics
sharp winter peaks
Starts Nov/Dec lasts 4-5 months
Little variability in timing or magnitude
At risk groups for RSV
Very young preterm babies (chronic lung disease of prematurity increases risk)
Very elderly
Prevention/how to mitigate RSV Risk
(textbook exam Q)
(not just for RSV - similar measures for all respiratory viruses)
- Breast feeding
- Vaccination (passive vaccine) to newborn babies during RSV season
- Education & awareness - parents & elderly carers
- Hygiene measures (tissue in bin after blow nose, wash hands; cover mouth when cough)
- Stay away from grandchildren/grandparents when ill (especially flu)
- Don’t send sick kids to school
- Prewarning hospital/clinics so patients can be put in different waiting rooms
- Cohorting - separate infected & non infected area (for staff and pts)
- Isolate in hospital
- Clean rooms/environmental contamination
- Ventilation
- Treatment as prevention (if there is treatment)
Legionella/Legionnaires Disease - where is it found
Environmental pathogen
Warm Stagnant water
Becomes a problem when water is aerosolised
- showers
- taps
- air conditioning (puddle of water behind AC units –> fan on)
- Jacuzzis
- Humidifiers
Also: cooling towers in factory plants –> water condenses on temperature gradient –> sumps of legionella –> windows –> spreads
Human = dead end host - can’t transmit to other humans
Legionella prevention
Shock dosing up water towers with toxic substance that kills legionella
Test water supply if suspect domestic source
Maintain water temp >55 degs (building regulations)
Good plumbing techniques - no dead legs
Regular flushing and disinfection
Adequate cleaning and chlorination
Legionella presentation & demographics
Incubation period: 2-10 days, typically 5-6 days
Flu like illness, muscle aches, tiredness, headache, dry cough, fever, pneumonia
Can progress to multi-organ failure
At risk groups for legionella
More common in men
Over 50s
Heavy smokers
10-15% mortality
Diagnosis and management of legionella
- detection of urinary antigen (false positive risk)
- culture from respiratory specimen = gold standard
- detection of legionella spp nucleic acid (e.g. by PCR) in LRT specimen
Management: Abx, supportive, intensive care
PH investigation for legionella
Try to identify the source
10 day exposure history
- healthcare setting, travel, car wash, care, domestic, workplace,
- are there any other local cases (6km radius)
May carry out water & environmental sampling
Surveillance of legionella
Not notifiable but Health Protection Team needs informing
Serious environmental issue
National enhanced surveillance scheme
European network monitors travel associated cases
Legionella epidemiology UK
steadily increasing since 1980
~500 cases 2019
1/2 travel associated
1/2 community acquired
Who enforces Legionella prevention & management England
Local authority environmental health officers OR health and safety executive
