respiratory infection Flashcards
what are the 7 bacteria/viruses we need to know for first year?
- Streptococcus pneumoniae
- Mycobacterium tuberculosis
- Legionella pneumophila
- Mycoplasma pneumoniae
- rhinhovirus
- influenza
- coronavirus
what defences are used for innate immunity?
- cilia
- alveolar macrophages: secrete antimicrobials, engulf and kill pathogens, recruit other immune cells, process and present to T cells
what defences are used for acquired immunity?
- B cell/T cell responses
- IgA secreted by plasma cells interferes with adherence and viral assembly
what are the inflammatory responses?
- macro = redness, swelling, heat, pain and loss of function
- micro = vasodilation, increased vascular permeability and inflammatory cell infiltrate
- can be acute or chronic
name some infections of the upper respiratory tract
- rhinitis
- sinusitis
- pharyngitis
- tonsilitis
- laryngitis
name some infections of the lower respiratory tract
- bronchitis
- bronchiolitis
- pneumonia
- pulmonary tuberculosis
- pulmonary abscesses
- empyema
what is the most common cause of a cold?
rhinovirus
how do you transmit the common cold?
- hand contact: virus remains viable for up to 2 hours on skin or several hours on surfaces droplet transmission from sneezing/coughing/breathing
- IP 2-3 days; symptoms last 3-10 days and up to 2 weeks in 25% of patients
what does bradykinin cause?
intranasal administration causes a sore throat and it also causes nasal congestion due to vasodilation
what causes the symptom sneezing?
mediated by stimulation of the trigeminal sensory nerves - histamine-mediated
what causes the symptom nasal discharge?
changes colour with increasing numbers of neutrophils due to myeloperoxidase
what causes the symptom of a cough?
mediated by the vagus nerve - inflammation has to extend to the larynx to trigger this; hyper-reactive response in URTI
what symptoms do cytokines bring about?
systemic symptoms such as fever
what are the differences between cold and flu?
cold
- appears gradually
- affects mainly your nose and throat (coryza)
- makes you feel unwell but you’re okay to carry on as normal
- usually no fever
flu
- appears quickly (within hours)
- affects more than just your nose and throat
- makes you feel exhausted and too unwell to carry on as normal
- high fevers
- may have lower respiratory tract infections
what causes the flu?
influenza A or B virus
what happens with uncomplicated influenza?
- 1-4 days
- abrupt onset of fever, cough, headache, myalgia and malaise, sore throat and nasal discharge
- acutely debilitating
- fever 38-42degrees, otherwise examination often unremarkable
what are the risk groups of complication of influenza?
- immunosupressed patients or chronic medical condtions
- pregnancy or 2 weeks postpartum
- age <2 or >65
- BMI >40
what are the complications of influenza?
- primary viral pneumonia
- secondary bacterial pneumonia
- CNS disease
- death
what are the 3 problems a virus must solve?
- must replicate inside a cell
- it must move from one infected cell to a new cell in order to persist in nature
- it must develop mechanisms to evade host defences
how does influenza work?
- the influenza virus haemagglutinin surface protein (H) binds sialic acids on cell surface glycoproteins and glycolipids in the respiratory tract
- this allows the influenza virus to enter the cell
- the neuraminidase (N) on the surface of the virus allows the virus to escape by cleaving sialic acid bonds: otherwise escaping virions all clump together
- the influenza virus has a segmented genome (8 parts) so can reassort if 2 different viruses infect the same cell
what are the influenza shift and drift?
point mutation versus whole segment switch
how do you treat and prevent influenza?
- active immunisation: against haemagglutinin and neuraminidase components
- tamiflu = oseltamivir = a neuraminidase inhibitor
- hand hygiene and droplet precautions
what is the pathophysiology of pneumonia?
- alveoli full of inflammation = blocks oxygen transfer
- fever, breathlessness, cough, sputum production, hypoxia, increased respiratory rate, pleuritic chest pain, sepsis
what is pneumonia?
infection of the lung parenchyma
how does radiology help to diagnose pneumonia?
- diagnosis required infiltrates on 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 outlines by surrounding consolidation
what are the classifications of pneumonia?
- typical vs atypical: but not very helpful, as there is no features in an individual patient that helps distinguish between them
- lobar vs bronchopneumonia: also not very helpful, descriptive, but doesn’t help management
- community vs hospital-acquired: more useful, as the pathogens involved differ in the % contributions
what are the 3 pathogens that cause community-acquired pneumonia?
Streptococcus pneumoniae
Mycoplasma pneumoniae
Legionella pneumophila
Streptococcus pneumoniae
- most common organism overall
- gram positive cocci
- risk factors: alcoholics, respiratory disease, smokers, hyposplenism, chronic heart disease, HIV, 50 to 100 fold increase invasive pneumococcal disease in HIV+
- acquired in nasopharynx
- asymptomatic carriage in 40-50%: smokers > non smoker
- prevention: vaccine
- treatment: penicillin
Mycoplasma pneumoniae
- most common cause of ambulatory ‘atypical pneumonia’
- classically young patient, vague constitutional upset, several week
- extra pulmonary symptoms very common
- lacks cell wall: resistant to penicillins, cannot grow on normal lab plates
- diagnosis by PCR of throat swabs (VTS)
- treatment: macrolides or tetracyclines
Legionella pneumophila
- can occur as sporadic infection or in outbreaks associated with a contaminated water source
- uncommon: 350 cases/year in E&W
- can cause severe, life threatening infection
- RFs = smoking and chronic lung disease
- diagnosis: don’t grow in routine culture, need special conditions and longer, urinary legionella antigen
healthcare-associated pneumonia
- definitions vary
- new onset at least >48 hours since admission
- hospitalised patients become colonised with hospital bacteria
- these may either be intrinsically most resistant to antibiotics or have acquired resistance mechanisms
- either way, broader spectrum antibiotics are used empirically
what is the pathology of tuberculosis?
- aerobic bacillus
- divides every 16-20 hours (slow) - lab extends culture to 56 days
- cell wall, but lacks phospholipid outer membrane
- doesn’t stain strongly with gram stain (weakly positive), retains stain after treatment with acids
- referred to as acid-fast bacillus (AFB)
- special stains: Ziehl-Neelson or auramine-rhodamine
how does tuberculosis cause infection?
1) infection is initiated by the inhalation of aerosol droplets that contain bacteria
2) the initial stages of infection are characterised by innate immune responses that involve the recruitment of inflammatory cells to the lungs
3) following bacterial dissemination to the draining lymph nodes, dendritic cell presentation of bacterial antigen leads to T cell priming and triggers and expansion of antigen-specific T cells, which are recruited to the lung
4) the recruitment of T cells, B cells, activated macrophages and other leukocytes leads to the establishment of granulomas, which can contain mycobacterium tuberculosis
what is latent vs active tuberculosis?
Latent TB
- dormant bacilli
- contained by host defences
- non-infectious
- asymptomatic
- Dx (diagnosis) by demonstrating host IR (immune response)
Active TB
- actively replicating bacilli
- may be infectious (site-dependant)
- symptomatic (site dependant)
- Dx by isolating AFBs, growing MTB or PCR positive
how do you manage tuberculosis?
- cure active disease
- reduce spread
- prevent reactivation
BY
1) prompt and adequate treatment
2) appropriate source isolation
3) contact tracing
what are the symptoms of coronavirus?
- new continuous dry cough
- fever over 37.8 degrees
- change of loss of sense of smell or taste
- the frequency of nausea, vomiting, abdominal pain, headache and sore throat increasing with age
- fever and runny nose are less common with age
- symptoms evolve over the course of the illness
- more severe symptoms develop later
- hospital admission is usually on 8-10
who are most at risk with covid?
- the single greatest risk of mortality from COVID-19 is increasing age
- the risk increases exponentially with age
- 80% deaths have been those ages 70 or over
what are the risk factors of covid?
- underlying medical problems
- clear evidence that certain black, asian and minority ethnic (BAME) groups have higher rates of ingestion and higher rates of serious disease, morbidity and morality from SARS-Cov-2 infection
- societal factors, such as occupation, house size, deprivation and access to healthcare can also increase susceptibility and worsen outcomes
when do you get administered to hospital with covid?
- oxygen sats <90%
- respiratory rate >30
- signs of severe respiratory distress
what are the possible complications of covid?
- high risk of thromboembolism
- glycemic issues: hyperglycemia, DKA
- acute kidney injury
- cardiac toxicity
- delirium in elderly
what are the treatments of covid?
- supportive care
- high flow oxygen
- dexametnasone
how do you prevent covid?
- PPE
- ventilation (environment)
- reducing encounters
- reducing contact/proximity
- hand washing
- immunisation
