20 Lower respiratory tract infections Flashcards
What are causes of laryngitis/ tracheitis
Lower respiratory tract continuous with upper. But lower tend to be more severe. Similar organisms
Parainfluenza - most common Influenza Rhinovirus RSV Adenovirus
Diptheria
H Influenzae
S Aureus
GAS
Diptheria caused by corynebacterium diptheriae. Can colonise pharynx in normal people. Exotoxin producing strains cause disease. Diptheria can also cause cutaneous diptheria. Disease in resource-poor settings
Bacteria adheres using pili on cell wall to pharynx. Multiplies locally. Toxin destroys epithelial cells/ polymorphs, and necrotic ulcer forms
What are signs of diptheria infection?
Why is diptheria serious condition?
Exudate on pharynx causing “false membrane”
Bull neck - enlarged cervical nodes
Nasopharyngeal diptheria can cause hoarseness, stridor, and life threatening respiratory obstruction
Exotoxin can be absorbed systemically causing fever, myocarditis, polyneuritis due to demyelination
Incubation period of diptheria
Route of spread
2-5 days
Droplet spread
Direct contact - cutaneous
Structure of diptheria toxin
How does diptheria toxin work
Fragment A - toxic fragment
Fragment B - binding
Toxin binds to cells, and uptaken by cells. Fragment A inactivates ribosomal protein synthesis, causing apoptosis.
Investigations diptheria
Treatment diptheria
Nasopharyngeal throat swab - bacterial culture
Isolation
Airway management
Benpen/ erythromycin
Diptheria antitoxin - produced in horse serum
Diptheria vaccination - as antibody level post infection may not be high enough
How to deal with contacts exposed to diptheria
Nasopharyngeal swab - assess if asymptomatic carrier
Erythromycin prophylaxis
Diptheria immunisation
Bordetella pertussis causes whooping cough. Usually disease in children.
Bacteria attach and multiply on ciliated respiratory mucosa, but do not invade deeper structures. Has filamentous haemagglutinin and fimbriae which allow it to attach
Which toxins does it produce
Pertussis toxin - has A and B unit. Toxin upregulates cAMP causing dysregulated immune response
Tracheal cytotoxin - cell wall component directly kills tracheal epithelial cells
Inhibits phagocytosis
Inhibits chemotaxis
Inhibit antibody production
Pertussis incubation period
Symptoms
Diagnosis
7-10 days
Initial catarrhal illness
1 week later non-productive cough develops, which becomes paroxysmal. Paroxysyms characterised by series of short cough producing copious sputum, followed by “whoop”
Nasopharyngeal swab
Treatment of whooping cough
Prevention
Isolate - infective up to 3 weeks after symptom onset
Macrolide - erythro/ clarithro/ azithro - appears to reduce severity and duration, and infectivity of patient
Prophylactic antibiotics for close contacts
Immunisation with DPT (diptheria/pertussis/tetanus) vaccine. Targetted program at pregnant mothers, as maternal antibodies confer some protection to newborns
Causes of acute bronchitis
Causes of acute exacerbation of chronic bronchitis
Adenovirus
Coronavirus
Influenza - can cause post-influenza pneumonia with strep pneumoniae
Rhinovirus
Mycoplasma pneumoniae
Secondary infection with strep pneumoniae/ h influenzae common
Chronic bronchitis cough with excessive mucus secretion. Infection appears to be one component, along with smoking and inhalation of noxious substances. Multiple bacteria can cause it, but microbiology analysis difficult, as often some can be commensals and not cause disease. Multiple viruses can cause it, and can lead to secondary bacterial infection
Why does bronchiolitis usually occur in children <2
Causes of bronchiolitis
Bronchioles in young children very narrow, so when lining cells become inflamed, can cause airway obstruction. Severe in babies, with peak mortality at 3 months of age. Older children it is limited to URTI
RSV 75%
Parainfluenza
Influenza
Metapneumovirus
How is RSV transmitted
Incubation period
When to outbreaks occur
How does in attach to enpithelial cells
Droplet
4-5 days
Winter
Outbreaks often spread in hospitals
G proteins to attach to cells
Fusion protein to penetrate cell membrane
Investigations for bronchiolitis
Treatment
Viral throat swab
Supportive
Rehydration
Bronchodilators
Oxygen
Ribavirin - shown some efficacy
Palivizumab - monoclonal antibody can be used as prophylaxis in children <2 high risk airway disease. Given before and during RSV season
RSV pooled immunoglobulin can be given to high risk children
How do microbes gain access to lower respiratory tract
Microbes must be <5mm to reach alveoli
If impaired defences (HIV) or preceeding viral infaction, organisms which do not normally cause infectionm can cause infections in healthy individuals
Inhalation of aerosolized material or aspiration normal flora
Via bloodstream
What are four descriptive terms used for pneumonia
Pneumonia causes respiratory distress by interfering with gas exchange in the lungs, and causes systemic upset (sepsis)
Lobar pneumonia - distinct involvement of one lobe. Polymorphs form exudate in response to infection - causes solidification. Can spread between adjacted lobes
Bronchopneumonia - diffuse patchy changes due to consolidation in small airways
Interstitial pneumonia - invasion of interstitium usually seen in viral infections/ PCP
Lung abscess - necrotizing pneumonia with cavitation and destruction
Pneumonia more commonly causes by viruses in children. Adults tends to be bacteria
Causes of CAP
- typicals
- atypicals (because causes extrapulmonary features). Usually intracellular, so don’t show up on basic investigations
Typicals - Strep pneumoniae Haemophilus influenzae Moraxella cattarhalis Group A Strep Klebsiella Aspiration pneumonia
Atypicals -
Mycoplasma pneumoniae
Chalmydia pneumoniae
Legionella pneumophila
Atypical zoonotic -
Chladmydia psittaci
Coxiella burnetti
Tularaemia
Atypical viral - Adenovirus Influenza Parainfluenza RSV Measles SARS/ MERS/ COVID
Causes of CAP
- following viral infection
- HIV positive
- lung cancer
Post - viral
Strep pneumoniae
Staph aureus
HIV positive
PCP
Mycobacterium species
CMV
Lung cancer -
Moraxella cattharalis
Causes of CAP
- cooling tower exposure
- abbatoir worker/ vet/ farmer
- animal hide importers, wool sorters
- legionella
- coxiella burnetti
- brucella species
- coxiella burnetti
- bacilus anthracis
Causes of CAP
- exposure infected birds
- exposure infected sheep/ goat/ cattle
- exposure to bats/ bat droppings
- chlamydia psitacci
- coxiella burnetti
- brucella species
- histoplasma capsulatum
Causes of CAP
- hotel air conditioning
- California/ New Mexico/ Texas travel
- SE Asia, South/ Central America
- legionella
- coccidioides immitis
- Burkholderia pseudomallei - melioidosis
Hospital acquired pneumonia associated with more gram negatives. This is due to respiratory tract being colonised from lower GI tract - reflux/ PPI use
Causes of HAP
- Immunocompromised e.g post-organ transplant
- ventilator associated
Immunocompromised
- PCP
- CMV
- Mycobacterium species
- Nocardia
- Aspergillus
Ventilator
- Pseudomonas aeruginosa
- Staph aureus
- Enterobacteriaceae - Klebsiella, E. Coli, proteus, Enterobacter, Serratia
Causes of CAP
- Cystic fibrosis
CF -
Staph aureus
Haemophilus
Pseudomonas
Symptoms of typical/ atypical pneumonia
Cough
SOB
Pleurisy
Fever
Diarrhoea
Renal/ liver dysfunction
Meningitis - pneumococcal can spread via blood
When to take sputum sample and why
If sputum shows organism but no polymorphs, could just be commensal.
Immunocompromised patient may not have neutrophil response.
Atypicals bacteria (except legionella) will not show up on gram stain
May need chest physio/ bronchoscopy for sputum
What are rapid tests for pneumococcal
Take sputum first thing in morning - sputum pools in lungs, and prevents contamination with food
Antigen testing of sputum/ urine for antigen by agglutination of antibody-coated latex particles. Urine tests cannot test sensitivities on
Serological tests for atypica pneumonia
Legionella
Mycoplasma
Chlamydia pneumonia/ psittaci
Coxiella burnetti
Legionella - Urinary antigen test or rapid agglutination test
Mycoplasma - Complement fixation (CFT), IgM by latex agglutination or ELISA
Chlamydia - microimmunofluouresence of ELISA using species-specific antigens
Coxiella - Complement fixation test
Antibiotic selection for CAP
First choice - Amoxicilin
Secondary to viral infection - co-amoxiclav
Aspiration - co-amoxiclav and gentamicin
Antibiotics selection for specific organisms
- Strep pneumoniae
- Staph aureus
- Haemophilus
- Klebsiella
- Atypicals
Amoxicillin is often not active against many other causes of pneumonia, co combination therapy usually used as first line.
Can prevent strep pneumoniae with vaccine comprising polysaccharide capsular antigens. For splenectomy patients and those with chronic disease
Strep pneumoniae - amox/ clarithromycin
Staph aureus - flucloaxacillin
Haemophilus - co-amoxiclav/ cefuroxime
Klebsiella - gent/ cipro
Atypicals - doxycycline
Viruses can invade the lung via bloodstream as well as directly to respiratory tract. They can sometimes cause initial damage, which allows bacterial infection
What are common causes of viral pneumonia, and what clinical condition do they produce
- Influenza A/B - can cause secondary bacterial infection. Type A causes pandemics, Type B epidemcis. Antiviral available
- Parainfluenza types 1-4 - croup/ pneumonia children, URTI adults. No treatment
- Measles - secondary bacterial infection. Can cause primary infection immunocompromised.
- RSV/ metapneumovirus - bronchiolitis children, URTI adults
- Adenovirus - pharyngitis. Occurs in military - vaccine available. Cidofovir/ ribavirin can help
- CMV - interstitial pneumonia immunocompromised patients. Ganciclovir/ valganciclovir/ foscarnet/ cidofovir and immunoglobulin available
- HSV - interstitial pneumonia - immunocompromised
- Varicella-zoster - penumonia in children chickenpox
Structure parainfluenza
How many types
(-) SS-RNA
Surface spikes have haemagluttinin plus neuraminidase on one spike, fusion protein on other spike
Types 1-3 cause pharyngitis, croup, otitis media, bronchiolitis, pneumonia
Type 4 causes mild disease
What are four types of influenza, and how easily does it spread
Type A - epidemics, occasionally pandemics. Birds resevoir host
Type B - epidemics, no animal hosts
Type C - minor URTI
Type D - infects cattle usually
Describe structure of influenza virus and role of each part
(-) sense SS-RNA - 8 segments
Nucleoprotein
Polymerase
(these 3 help form ribonuceleoprotein)
Matrix protein
Lipid envelope
Haemagluttinin - approx 500 spikes - bind to host cell. H1-H16 different types
Neuraminidase - approx 100 spikes - release virus from cell. N1-N9