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
Aspiration pneumonia
- impaired gag and swallowing reflex, altered mental status e.g. convulsion
Pathogenesis:
- chemical pneumonitis
- bronchial obstruction with particulate
- bacterial aspiration pneumonia
Causative agent (ORAL flora):
- Anaerobes (Bacteroides)
- Streptococcus
- Gram -ve bacilli
- S. aureus
Symptoms:
- insidious (fever, weight loss)
Treatment:
- Broad-spectrum (to cover aerobic + anaerobic): quinolone, tetracycline
Lung abscess
Pre-disposing conditions:
- aspiration
- poor dental hygiene
- bronchiectasis
- septic embolisation (infective endocarditis)
- amoebic lung abscess
Causative agent:
- mixed ORAL flora
Empyema thoracis (pleural cavity abscess)
- complications of pneumonia
- complications of surgery/trauma
- secondary to subdiaphragmatic sepsis
Causative agent:
- secondary to pneumonia: S. pneumoniae, S. aureus
- secondary to surgery/trauma: gram -ve bacilli, anaerobe
Treatment:
- drainage
- antibiotics: according to pathogen
- decortication (removal of pleura)
Tuberculosis
Bacteria:
Mycobacterium tuberculosis
- gram +ve bacilli but not stained by Gram stain
- obligate aerobe, long generation time (16-18 hours): Chronic infection
- Lowenstein-Jensen medium: bread crumb colony
- Acid-fast (resistance to acid treatment during staining —> therefore use Ziehl-Neelsen stain: Red)
- fluorescent stain (auramine O)
- Mycolic acid in cell wall (very high lipid content)
- non-motile, non-sporulating
- resistance to acid/alkali, chemical disinfectant, drying
- susceptibility to heat and UV
- M. tuberculosis: tuberculosis, M. leprae: leprosy
Pathogenesis:
- survival in macrophage: inhibit fusion of lysosome in phagosome
- cellular immunity —> tissue damage
Pathology:
- Granulomatous inflammation —> Langhans giant cell
- Caseous necrosis
- Cavitation
- Cell-mediated immunity
- Primary tuberculosis: unrestrained bacterial multiplication at the beginning
- Post-primary tuberculosis: reactivation
Transmission:
- Airborne (droplet nuclei)
- M. bovis: milk
Site:
- Pulmonary
- Extrapulmonary
Diagnosis:
- Definitive diagnosis: Culture: 8-12 weeks
- Ziehl-Neelsen stain / acid-fast stain
- Tuberculin skin test / Mantoux test: purified protein derivative (intradermal) —> delayed hypersensitivity reaction (read 2-3 days after) —> NOT definitive (false positive: other mycobacteria, BCG vaccination)
- PCR on bronchial fluids
- histopathology
Treatment (multiple agents required >=4):
1st line:
- Rifampicin
- Isoniazid
- Pyrazinamide
- Ethambutol
- Streptomycin
2nd line: fluoroquinolone, amikacin, kanamycin
- Duration: 4-6 months
- Hepatotoxicity, ototoxicity, eye toxicity
- MDR-TB, XDR-TB, TDR-TB
Prevention:
BCG vaccine (Bacille Calmette-Guerin vaccine)
- attenuated M. bovis
- efficacy highly variable
Pneumocystosis
Fungal:
- Pneumocystis jirovecii
- colonise in healthy individuals
Transmission:
- inhalation
Risk factors:
- immunocompromised
- HIV/AIDS (INDICATOR disease)
Symptoms:
- pulmonary infection
- bilateral diffuse infiltrate in X-ray
- hypoxaemia
Diagnosis:
- Bronchoalveolar lavage (BAL)
- induced sputum (expectorated NOT ok)
- biopsy
- Methenamine silver stain
- PCR
Treatment:
- supportive
- chemotherapy: Cotrimoxazole, Pentamidine
Prevention:
- chemoprophylaxis in HIV/transplant patients
Influenza
Orthomyxoviridae:
- enveloped RNA virus
- Nucleocapsid (8 segments of ssRNA except C/D, RNA polymerase, nucleoprotein)
- Types: Influenzavirus A, B (important and common in human), C, D
—> classification based on NP (nucleoprotein), M1 (matrix) and M2 (ion channel)protein
- Subtypes: depend on HA and NA (only for influenza A)
—> Haemagglutinin (17 types: H1-18): attachment
—> Neuraminidase (10 types: N1-11): release
- Antigenic drift: minor changes within influenza subtype
- Antigenic shift: major changes in antigen: new HA/NA
Influenza A:
- H3N2, H1N1
- avian: H5N1
- animal: swine H1N1 (combined genes from human, pig, bird flu)
Peak in winter, HK: feb-mar, jul-aug
Transmission:
- droplets —> local multiplication at respiratory epithelium
- aerosols
- bird droppings
- contaminated surface
Symptoms:
- incubation: 18-72 hours —> rapid onset
- virus shedding: <24 hours to 3-5 days
- Dry cough, nasal disachrge
- high fever, sudden onset of myalgia, malaise
- Recover within a week
Complications:
- viral pneumonia
- secondary bacterial pneumonia
- Reye syndrome
Diagnosis:
- clinical diagnosis
- viral antigen
- PCR
- viral culture
- serology NOT useful
Treatment:
- symptomatic: analgesic, antipyretic (avoid aspirin and NSAID)
- Antiviral (ONLY effective if given in EARLY stage):
1. Neuraminidase inhibitor: oseltamivir, zanamivir, peramivir
2. Baloxavir
Prevention:
- Vaccine:
1. inactivated vaccine (2A+2B: trivalent / quadrivalent: IM injection)
2. live-attenuated: intranasal
3. recombinant: recombinant haemagglutinin: IM injection
- infection control
- pandemic influenza vaccine
- chemoprophylaxis
