L60, L68, L69: Respiratory Tract Infections Flashcards
Defence mechanisms of respiratory tract
- Nasopharynx
- nasal hairs
- concha
- mucociliary apparatus
- sIgA - Oropharynx
- saliva
- pH
- bacteria interference - Trachea and bronchi
- mucociliary apparatus
- cough and epiglottic reflex
- sharp angled branching of airway - Terminal airways and alveoli
- alveolar macrophage
- cell-mediated immunity
- alveolar lining fluid
Pharyngitis
Most: VIRAL
Bacterial: Streptococcus pyogenes (Group A strep)
Transmission:
- person-to-person
- asymptomatic carriage possible
- 2-4 days incubation, subside in 1 week
Symptom:
- abrupt onset (sore throat, fever, malaise)
- hyperaemic tonsils with whitish exudate
- enlarged tender lymph nodes
- lymphoid hyperplasia of posterior pharynx
Diagnosis
- Definitive diagnosis: Throat swab, antigen detection test
Treatment
- Penicillin
Complications:
- suppurative: abscess, pneumonia
- non-suppurative: Acute rheumatic fever (molecular mimicry, heart-reactive antibodies HRA, JONES criteria), Post-streptococcal glomerulonephritis
Viral vs Bacterial pharyngitis
Bacterial:
- Abrupt onset
- Painful
- Enlarged tender lymph nodes
- Swollen, exudative, red tonsils
- Not affected eyes/nose
Viral
- Gradual onset
- Uncomfortable
- Not enlarged lymph nodes
- Ulcer, vesicle, red tonsils
- Watery eyes and running nose
Diphtheria
- good childhood immunization coverage
Bacteria: Corynebacterium diphtheriae
- gram +ve
- unencapsulated
- non-sporulating, non-motile
- Metachromatic granules (Albert stain), Chinese character palisades
- Confirmed by biochemical tests
- Loeffler medium, potassium tellurite medium
Transmission:
- droplet
- contact with secretions
- asymptomatic carrier
Symptom:
- pseudomembrane (dead tissue)
- sore throat
- fever
- myocardial depression, neuropathy
- Cutaneous diphtheria (non-healing skin ulcer)
Diagnosis:
- Definitive diagnosis: Biochemical test, metachromatic granules (Albert stain)
Pathogenesis:
- exotoxin (tox gene by bacteriophage) —> inactivation of elongation factor 2 in protein synthesis
- systemic effect of exotoxin
Treatment:
- Diphtheria antitoxin
- Penicillin
Prevention:
- Diphtheria toxoid vaccination
Acute epiglottitis
Bacteria: Haemophilus influenzae type b (beta haemolytic strep, staph aureus)
- 2-4 years old mainly
Symptom:
- rapid onset of fever
- dysphonia, dysphagia, airway obstruction
- medical emergency, may need intubation
Diagnosis:
- laryngoscopes
- lateral neck x-ray
Treatment:
- Third generation cephalosporin (ceftriaxone, cefotaxime)
Acute sinusitis
- obstruction of sinus drainage
- pre-existing URT viral infection
- allergy
- swelling of inflamed mucosal lining
Causative agent:
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
- Viruses (rhino, para, adeno, influenza)
Symptoms:
- purulent nasal and postnasal discharge
- facial pain
- headache
Complications:
- LOCAL extension:
—> intra-orbital
—> intra-cranial
—> osteomyelitis of frontal bone
Diagnosis:
- physical examination, symptomatology
- sinus X-ray
- Definitive: sinus puncture + aspiration of sinus content
- culture NOT reliable
Treatment:
- Antibiotics: Amoxicillin-clavulanate, ampicillin-sulbactam, cefuroxime
- Surgical: sinus drainage
Otitis externa
- infection of external auditory canal
Bacteria:
- Staphylococcus aureus
- Pseudomonas aeruginosa
Treatment:
- Systemic antibiotics
- surgical drainage of abscess
Acute otitis media
- 6-24 months mainly
Bacteria:
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
Predisposing factors:
- bacterial colonisation of nasopharynx secondary to viral URT infection
- anatomical defects (cleft palate)
- abnormalities of Eustachian tube
- immunodeficiencies
Pathogenesis:
- Eustachian tube dysfunction
- Eustachian tube obstruction —> accumulation of fluid and secretion —> risk of infection
Symptoms:
- ear pain, drainage
- hearing loss
- fluid in middle ear
- erythema of tympanic membrane
Diagnosis:
- Definitive: Tympanocentesis (not routine)
- culture NOT useful
Treatment:
- Amoxicillin-clavulanate
- Cefuroxime
Tracheolaryngobronchitis (Croup)
- inflammation of subglottic area —> dyspnea + inspiratory stridor
- 3 month to 3 years
Causative agent:
- Mainly Virus (PARAinfluenza, influenza, RSV)
- bacteria: mycoplasma pneumoniae
Symptom:
- dyspnea
- inspiratory stridor
- tachypnea
- hypoxaemia
Diagnosis:
- Viral antigen detection
- PCR
Treatment:
- supportive (oxygen, bronchodilator)
Pertussis (Whooping cough)
Bacteria:
- Bordetella pertussis
—> gram -ve coccobacillus
—> filamentous Haemagglutinin
—> Pertussis toxin and other toxins
Transmission:
- droplet
- endemic
Symptoms, Incubation period:
- <1 week to >3 week
- Catarrhal phase: rhinorrhoea, conjunctival injection, malaise
- Paroxysmal phase: short expiratory burst followed by inspiratory gasp (whoop)
- Convalescent phase
Diagnosis:
- Culture of nasopharyngeal aspirate
- Swab on Bordet-Gengou medium
- symptomatology (children: whoop, adults: chronic cough)
Complications:
- pneumonia
- subconjunctival bleeding
- insucking intercostal space
Treatment:
- Macrolides
Prevention:
- acellular vaccine (filamentous Haemagglutinin, pertussis toxin)
—> combination: diphtheria toxoid, tetanus toxoid, inactivated poliomyelitis
- whole-cell killed vaccine
Pneumonia
Inflammation of lung parenchyma
Causative agent for Community-acquired pneumonia:
Bacteria:
- Streptococcus pneumoniae
- Haemophilus influenzae
- Staphylococcus aureus
- (Mycobacterium tuberculosis, mycoplasma pneumoniae)
Virus:
- RSV (children, infant)
- influenza, parainfluenza, coronavirus
Transmission:
- inhalation of infectious particles
- aspiration of secretion from mouth/nasopharynx (prior URT colonisation)
Definitive diagnosis: Culture of respiratory tract specimen
- history (age, underlying illness, travel, animal contact, defect in resistance)
- physical examination (pulse-temperature deficit)
- X-ray: patchy, diffuse white shadows
- Sputum: macroscopic, colour, amount, consistency, rusty (S. pneumoniae), currant-jelly (Klebsiella pneumoniae)
- blood gas, blood count
- Bronchoalveolar lavage (BAL) + fibreoptic bronchoscopy
- pleural fluid aspiration, culture
- biopsy
- PCR: virus, atypical pathogen
- Serology: atypical antigen
- Viral antigen detection: immunofluorescent
- urine antigen detection: S. pneumoniae, Legionella pneumophila
Treatment: (empirical/specific, inpatient/outpatient, oral/parenteral)
- supportive: oxygen
- empirical antibiotic: Beta-lactam +/- Macrolide (Tetracycline)
Acute community-acquired pneumonia
Causative agent:
- Streptococcus (old age, smoking, COPD)
- Haemophilus influenzae
- Staphylococcus aureus (post-influenza)
- (Klebsiella pneumoniae)
- Viruses (RSV)
Symptoms:
- fever, chills
- pleuritic chest pain
- mucopurulent sputum
Prevention:
- S. pneumoniae: Pneumococcal vaccine: polysaccharide (23-valent), conjugate (13-valent)
Atypical pneumonia syndrome
- No significant pathogen in routine culture
- Not respond to beta-lactate
- prolonged course
Causative agent:
Bacteria:
- Mycoplasma pneumoniae
- Legionella pneumophila
- Chlamydophila pneumoniae
- Virus: influenza, adeno, para, RSV, corona
Legionella pneumophila
- aerobic, non-sporulating, gram -ve bacilli
- most common: serogroup 1
Transmission:
- artificial water sources: cooling tower
- aerosolisation and aspiration
Symptoms:
- Pontiac fever: acute, self-limiting, flu-like without pneumonia
- Legionnaires’ disease: pneumonia
Diagnosis:
- Urine antigen detection
- bacterial culture
Treatment:
- Macrolide
- Fluoroquinolone
- beta-lactam NOT useful
Nosocomial pneumonia
Risk factors:
- age, underlying disease, intubation, gastric acid suppressant, altered mental status
Causative agent:
- Gram-negative bacilli: E. coli, K. pneumoniae, P. aeruginosa, MRSA
