Respiratory Tract Infections Flashcards
What are the main defences of the upper respiratory tract against infection?
Muco-ciliary escalator (ciliated pseudostratified columnar epithelium)
Cough/sneezing reflex
Lymphoid follicles of pharynx & tonsils, alveolar macrophages, IgA & IgG
What are some common organisms present in the upper respiratory tract?
Normal flora: viridians Strep. Neisseria spp. Anaerobes Candida spp.
Transient colonisation:
Strep. pneumoniae
Strep. pyogenes
H. influenzae
Immunocompromised/long-term hospitalisation:
Pseudomonas aeruginosa
E. coli
Less common:
What are the possible sites of infection in the upper respiratory tract and the organisms implicated?
Rhinitis (common cold) Pharyngitis Epiglottitis Laryngitis Tracheitis Sinusitis Otitis media
Viruses: rhinovirus, coronavirus, (para)influenza, RSV Bacterial superinfection (virus + bacteria) common with sinusitis/otitis media -> causes mastoiditis, meningitis, brain abscesses
What are the possible sites of infection in the lower respiratory tract?
Bronchitis:
Acute (viruses & bacteria) —> may lead to pneumonia
Chronic (not primarily infective)
Pneumonia (pulmonary parenchyma)
What is the definition of pneumonia? What is the difference between pneumonia and pneumonitis?
Infection of pulmonary parenchyma with consolidation (alveoli filled with fluid produced by inflammatory cells -> heavy, stiff lung)
Distal airspaces filled with inflammatory exudate, impairing gas exchange
PNEUMONITIS = non-infective inflammatory disease
What are some of the common bacteria implicated in community-acquired pneumonia?
S. pneumoniae (elderly, co-morbidity, acute onset, high fever, pleuritic pain)
Moraxella cattarhalis (COPD)
H. influenzae (COPD)
Kleb. pneumoniae (thrombocytopenia & leucopenia)
What are some of the atypical bacteria implicated in community-acquired pneumonia?
Chlamydia spp. (contact with birds) e.g. haemophilia
Mycoplasma pneumoniae (no cell wall; young, prior antibiotics, extra-pulmonary involvement e.g. haemolysis, skin, joints)
Legionella (recent travel & exposure to contaminated aerosols; young, smokers, multi-system involvement)
What are some of the viruses implicated in community-acquired pneumonia?
(para)influenzae (give antivirals to pregannt/immunocomprimised - oseltamivir & zanamivir)
Respiratory syncytial virus (RSV)
note: patchy/diffuse ground glass opacity on CXR
Severe viral pneumonia causes necrosis/haemorrhage into lung parenchyma -> similar symptoms to adult respiratory distress syndrome
What are some of the bacteria implicated in hospital-acquired pneumonia? What is the definition of hospital-acquired pneumonia?
Pneumonia occurring 48hrs after hospital admission; especially ITU, ventilated patients, post-surgical patients (intubated, poor ventilation, immobile, aspiration, immunocompromised, antibiotics)
Gram-ve enteric bacteria
Pseudomonas
MRSA (post-viral, IV drug use)
M. tuberculosis + atypical mycobacteria
Coxiella (animal contact)
Strep. millei (dental infections; abdominal source)
Aspiration pneumonia: bacteria from GI tract enters lungs
- anaerobes, oral flora, mixed (e.g. viridians strep. + anaerobes)
What are some organisms implicated in pneumonia in immunocompromised patients?
Candida
Aspergillus
Pneumocystitis jirovecii -> pneumocystis pneumonia (PCP) -> diffuse hilar shadowing
Opportunistic viruses
Protozoa
What is aspiration pneumonia? What are some risks/causes?
Aspiration of exogenous material or endogenous secretions into the respiratory tract (own flora/environmental flora aspirated)
- neurological dysphagia
- epilepsy
- alcoholics
- drowning
- drug overdose
- nursing home residents
Compare the presentation and organisms involved in lobar and bronchopneumonia.
LOBAR PNEUMONIA: (S. pneumoniae)
- confluent consolidation involving a complete lung lobe
- community-acquired
- acute onset
- acute inflammatory response: exudation of fibrin-rich fluid (neutrophil & macrophage infiltration)
note: usually at base of lungs (atypical organisms implicated in upper lobes)
BRONCHOPNEUMONIA: (S. pneumoniae & H. influenzae + aspirates inc. S. aureus, anaerobes, coliforms)
- starts in airways and spreads to adjacent alveoli and lung tissue, often in the context of pre-existing disease
- complication of influenza/viral infection/aspiration of gastric contents, cardiac failure, COPD
- patchy consolidation not confined by lobar architecture
Compare the causative organisms and complications of acute and chronic pneumonia.
ACUTE: test for most common bacteria
- resolution & organisation -> fibrous scarring (if microbe is not cleared can remain latent and lead to chronic/recurrent pneumonia)
- complications include lung abscesses, bronchiectasis, empyema
CHRONIC: test for mycobacteria, fungi, & atypical bacteria
- susceptible to recurrent pneumonia (e.g. as in cystic fibrosis patients)
What is whooping cough?
Bordetella pertussis
Transmission: droplet
Epidemic every 4yrs in older generation
Cold-like symptoms causes severe coughing for 2-3 months, which then causes whoop/vomiting
Treat with erythromycin
Vaccinate in childhood & pregnant women (does not last throughout life)
Define bronchiectasis.
Widening of the bronchi
Causes:
- congenital
- infection e.g. whooping cough, measles (childhood)
- obstruction e.g. foreign object, growth
Define empyema.
Pus in pleural cavity
What are some signs and symptoms of pneumonia?
- febrile symptoms (fever, chills, sweats, rigors)
- cough: sputum may be clear, purulent, “rust-coloured”, or haemoptysis
- dyspnoea
- myalgia
- pleuritic pain
- malaise
- anorexia
- vomiting
- headache
- diarrhoea
- wheeze
- bronchial breath sounds
- crackles
- dullness to percussion
- reduced vocal resonance
What are the characteristics of pleuritic pain?
Chest pain exacerbated by forceful breathing
+ perceived dyspnoea (due to suppressed ventilation)
note: also called pleurisy
What are some of the important investigations for pneumonia?
CXR O2 sats. & ABG FBC, WCC, platelets U&E, LFTs, CRP Sputum sample appearance (?mucoid, ?purulent, ?blood) Culture, Gram stain & acid fast PCR (viruses) Antigen detection (Legionella, pneumococcus - urine) Antibody detection (serology)
How can samples be obtained for investigation in pneumonia?
Sputum
Nose/throat swabs (viral cause suspected)
Endotracheal aspirates
Broncho-alveolar lavage fluid (if cannot cough up sputum)
Open lung biopsy (if cannot cough up sputum)
What is the management of pneumonia?
Depends on CURB-65 score
?confusion, high urea, high resp. rate, high BP, >65yrs
(score >2 -> hospitalisation +/- ITU)
Antibiotics:
- amoxicillin or co-amoxiclav (note: amoxicillin resistance in E. Europe & SE Asia)
- levofloxacin for Legionella
- tetracyclines/macrolides for atypical organisms
- poor response/atypical presentation -> discuss with microbiology
Prevention:
- flu vaccine annually for high risk patients
- pneumococcal vaccine
- oral penicillin/erythromycin for patients at high risk of infection e.g. asplenic, dysfunctional spleen, immunodeficiency
When should pneumonia patients be sent to the ITU?
Respiratory failure
Hypercapnia
Worsening metabolic acidosis
Hypotension despite fluids
What is chronic maxillary sinusitis? How is it diagnosed? How is it treated?
Infection causes mucosal inflammation and oedema in the maxillary sinus
Exudate retained in maxillary sinus due to the blockage of the ostium by congested mucosa and inflammation, preventing drainage into nasal cavity
- pain (high pressure)
- halitosis can occur due to chronic dental disease (e.g. dental apical abscess), poor dental hygiene, anaerobic organisms in mucus
Diagnosis: plain X-ray/CT of sinuses shows opacity in maxillary sinus due to fluid
Recurrence can occur despite antibiotic treatment due to blocked drainage - may require surgical drainage of maxillary antrum & teeth extraction
Why are asplenic patients vulnerable to bacterial pneumonia?
Defective alternate complement pathway & deficient in serum opsonin activity & reduced blood filtering
Vulnerable to encapsulated bacteria inc. Strep. pneumoniae
