respiratory tract infections Flashcards
what are bacterial causes for respiratory tract infections
Streptococcus pneumoniae
Mycobacterium tuberculosis
Legionella pneumophila
Mycoplasma pneumoniae
what are viral causes for respiratory tract infections
Rhinovirus
Influenza
Corona virus (human coronaviruses and SARS coronavirus)
what are fungal causes for respiratory tract infections
Aspergillus fumigatus
Pneumocystis jirovecii
what is the pathogenesis of respiratory tract infections
Lungs constantly exposed to particulate material and microbes from upper airway
Lower airway usually devoid of conventional pathogens
what is the innate immunity in respiratory tract infections
cilia (mucocilliary escalator removing debris and pathogens) Alveolar macrophages (secrete anti microbials, engulf and kill pathogens, recruit other immune cells and process and present antigens to t cells)
what is the acquired immunity in respiratory tract infections
B/T cell responses
IgA secreted by plasma cells interferes with adherence and viral assembly
what is the bodies response to infection
Inflammation – body’s response to insult
Macro – redness, swelling, heat, pain and loss. Of function
Micro – vasodilation, increased vascular permeability and inflammatory cell infiltration
Acute or chronic
what infections affect the upper respiratory tracts
Rhinitis Sinusitis Pharyngitis Tonsilitis Laryngitis
what infections affect the lower respiratory tracts
Bronchitis Bronchiolitis Pneumonia Pulmonary tuberculosis Pulmonary abscesses Emphysema
what are the two. common respiratory viruses and their associated symptoms
Rhinovirus: common cold alongside human corona virus (zoonotic – severe respiratory illness)
Influenza – flu
what is the common cold
5-7 x year in pre school children, 2-3 in adults
Account for 40% of all time lost from work
>200 viral subtypes
Rhinovirus is commonest 30-50% and human corona virus is 10-15%
how is the common cold spread
Hand contact (viable on skin for up to 2 hours, several on surfaces)
Droplet transmission from sneezing/coughing/breathing
IP 2-3 days, symptoms 3-10 days and 2 weeks in 25% of patients
what causes symptoms of a cold
intranasal administration of bradykinins causes a sore throat and nasal congestion due to vasodilation
Sneezing is mediated by stimulation of trigeminal sensory nerves – histamine mediated
Nasal discharge changes colour with increasing numbers of neutrophils (white -yellow -green) due to myeloperoxidase
Cough is mediated by the vagus nerve – inflammation has to extend to the larynx to trigger this, hyper reactive response in URTI
Cytokines responsible for systemic symptoms such as fever
how do you tell the difference between cold and flu
Cold Appears gradually Affects mainly nose and throat (coryza) Feel unwell but ok to carry on as normal Usually no fever
Flu Quickly -few hours Affects more than coryza Fell exhausted and too unwell to carry on as normal High fevers May have lower resp tract features
what is influenza
Caused by influenza A or B virus
Occurs in outbreaks and epidemics worldwide, usually in winter season so swaps hemispheres
Uncomplicated influenza
IP 1-4 days
Abrupt onset of fever + cough, headache, myalgia and malaise, sore throat nasal discharge
Acutely debilitating
Fever 38-41 C, otherwise exam often unremarkable
what are risk groups for influenza complications
Primary viral pneumonia
Secondary bacterial pneumonia
CNS disease
Deaths (est mortality rate) among people infected in US is about 0.13%
what are 3 issues a virus must overcome
Replicate inside a cell
Move from infected cell to new cell (and new host) in order to persist in nature
Must develop mechanism to evade host defences
what is the structure of influenza
Haemagglutinin surface proteins must bind to sialic acid on cell surface glycoproteins and glycolipids in the resp tract. Allows influenza to enter cell
The neuraminidase on the surface of the virus allows the virus to escape by cleaving sialic acid bonds – otherwise escaping virions clump together
The virus has a segmented genome (8 parts) so can reassort if 2 different viruses infect the same cell
what is influenza shift and drift
Point mutations each time to change the outer side of the Virus
Alter H so it can evade neutralising antibodies
Antigenic shift is a massive change - whole segment switch to form a whole new virus =pandemic as nobody has any immunity
what are options for treatment and prevention of influenza
Active immunisation against H and N components
Hand hygiene and droplet precautions
what is the pathophysiology od pneumonia
Infection of the lung parenchyma
Alveoli full of inflammation = blocks oxygen transfer
Fever, breathlessness, cough, sputum production, hypoxia, inc resp rate, pleuritic chest pain and sepsis
how is pneumonia diagnosed
Radiology
Diagnosis of pneumonia requires infiltrates on a plain CXR with supporting clinical features
Consolidation – alveoli and bronchioles completely filled with inflammatory debris, pus, pathogens
Heart borders or diaphragm obscured due to loss of solid gas interface
Air bronchograms – air in larger bronchi outlined by surrounding consolidation
how is pneumonia classified
Typical vs atypical or lobar vs bronchopneumonia – descriptive, no help for management
Community vs hospital acquired – more useful as pathogens differ in their % contribution and aids management
Community acquired pneumonia pathogens
Resp viruses probably responsible for 1/3
what is streptococcus pneumoniae
Commonest organism overall
Gram positive cocci
what are the risk factors for streptococcus pneumoniae
resp disease, smokers, hyposplenism, chd, HIV (50 to 100 fold increase in invasive pneumococcal disease in HIV+)
Acquired in nasopharynx
Asymptomatic carriage in 40-50%
Smokers greater
what is mycoplasma pneumoniae
Commonest cause of ambulatory atypical pneumonia
Classically young patients, vague constitutional upset, can last several weeks
Extrapulmonary symptoms very common
what is legionella pneumophilia
Can occur as a sporadic infection in outbreaks associated with a contaminated water source (travel and nosocomial acquisition)
uncommon -350 cases a year in England and wales
Can causes sev, life threatening infection
what are the risk factors for legionella pneumophilia
smoking and chronic lung disease
how is streptococcus pneumoniae treated and diagnosed
Prevention via vaccine
Treat with penicillin
how is mycoplasma pneumoniae treat and diagnosed
Lacks cell wall, resistant to penicillin and cannot grow on normal lab plates
Diagnosis by PCR throat swab (VTS)
Treat macrolides and tetracyclines
how is legionella pneumophilia treat and diagnosed
Diagnosis doesn’t grow on routine culture – need special conditions and longer time (eg two weeks)
Urinary legionella antigen
Treat macrolides or quinolones
what is healthcare associated pneumonia
More increasing severity and burden
New onset >48 hours since admission
Hospitalised patients become colonised with hospital bacteria
May be intrinsically more resistant to antibiotics or have acquired resistance mechanisms
Either way broader spectrum antibiotics are used empirically
what is the global issue of TB
Global problem
In 2017 8 countries accounted for 2/3 cases of new TB cases: china, indonesia, philippines, Pakistan, Nigeria, Bangladesh and SA
WHO 2017 est 10 million new cases and 1.6 million deaths worldwide
¼ of world’s pop has latent TB
How does TB affect the UK
71% cases born outside UK
Rates 13x higher than if born in UK
12% HAVE SOCIAL RISK FACTOR (homeless, prison, drug use etc)
2.8% HIV +
What is the pathology of TB
Aerobic bacillus
Divides every 16-20 hours (slow) lab extends cultures to 56 days
Cell wall but lacks phospholipid outer membrane so doesn’t stain well with gram but retains stain after acid treatment (acid fast bacillus)
Special stains – ziehl-neelsen or auramine-rhodamine
How does TB affect the body
initiated by inhalation of droplets with bacteria
innate immune response and recruitment of inflammatory cells to lung
dissemination
draining lymph node
expansion of antigen specific T cells
recruit adaptive immune cells to test granulomas with mycobacterium TB
What is latent TB
Dormant bacilli Contained by host defences Non infectious Asymptomatic Dx by demonstrating host IR
What is active TB
Actively replicating bacilli
May be infectious (site dependant)
Symptomatic (site dependant)
Dx by isolating AFBs, growing MTB or PCR positive
What is the aim of TB management
Aim Cure active disease Reduce spread Prevent reactivation By Prompt and adequate treatment Appropriate source isolation By contact tracing
what are the types of TB
Primary complex from infection
healed lesion
latent lesion (can reactivate into post primary TB or reinfection due to HIV, transplant or greater chances if diabetic, IVDU and smoker)
progressive primary TB
what is SARS coronavirus 2
Beta coronavirus
Identified in Dec 2019 and sequenced in Jan 2020
Likely bat in origin to humans (via another species?)
Droplet spread (+aerosol + contact)
Spike protein (S) binds to ACE2 receptor on airway epithelial cells (gut, other organs)
what is the chain of infection
infectious agent: SARS CoV2
reservoir: humans or other mammals
portal of exit: coughing, talking, sneezing
mode of transmission: droplet, aerosol, contact
portal of entry: mouth, nose, eyes
susceptible host: susceptible people
what are symptoms of SARS CoV2
New cont dry cough
Fever over 37.8C
Change or loss of sense of smell or taste
Range of symptoms freq of nausea, vomiting, abdominal pain, headache, sore throat inc with age
Symptoms evolve over course of illness
More sev symptoms develop later
Hospital admission is usually on days 8-10
What is COVID-19
The clinical syndrome associated with SARS CoV2
80% have asymptomatic to moderate disease and recover with no hospital
15% severe inc pneumonia
5% critically unwell, eg septic shock and multi organ failure and resp failure
Overall infection rate estimated to be 0.9% but varies according to age and sex
Lower in young people (0.5% for those 45-64 years) and higher if over 75 (11.6%)
Who is most at risk of COVID-19
single greatest risk for mortality is increasing age
Risk inc exponentially with age
80% death have been in those aged 70 years and over
What are risk factors of COVID-19
Underlying medical problems like hypertension, IHD, diabetes, male gender have an increased risk of severe disease
Clear evidence that BAME groups have higher rates of infection and higher rates of serious disease, morbidity and mortality infection
Societal factors such as occupation, household size, deprivation and access to healthcare can also increase susceptibility to COVID-19 and worsen outcomes
When should severe conditions due to COVID-19 be admitted
Oxygen sats less than 90%
Resp rate >30
Signs of sev resp distress
what are complications of COVID-19
High risk of thromboembolism Glycemic issues – hyperglycemia, DKA Acute kidney injury Cardiac toxicity Delirium in elderly
How is COVID-19 treated
supportive care
High flow oxygen
Dexamethasone
how can COVID-19 be prevented
Personal and protective equipment Ventilation (environment) Reducing encounters Reducing contact/ proximity Hand washing Immunisation
