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Chapter 21
Infectious Diseases Affecting the Respiratory System
Chapter Outline
21.1. The Respiratory Tract and Its Defenses
A. The most common place for infectious agents to gain access to the body
B. The upper respiratory tract
1. Mouth, nose, nasal cavity and the sinuses above it
2. Throat or pharynx
3. The epiglottis and larynx
C. The lower respiratory tract
1. Trachea
2. Bronchi and bronchioles in the lungs
3. Alveoli
D. Defenses
1. Nasal hair
2. Ciliated epithelium of the trachea and bronchi
3. Mucus
4. Coughing, sneezing, swallowing
5. Macrophages in lungs
6. Lymphoid tissue (tonsils) in throat
7. Secretory IgA in mucus
21.2. Normal Biota of the Respiratory Tract
A. Some bacteria capable of causing serious disease are frequently present in the upper
respiratory tract as “normal” biota:
1. Streptococcus pyogenes, Haemophilus influenzae, Streptococcus pneumonia
2. Neisseria meningitidis and Staphylococcus aureus
B. Others found in the upper respiratory tract include:
1. Nonhemolytic and alpha hemolytic streptococci, Moraxella and Corynebacterium
species and Candida albicans
C. Normal biota is generally limited to the upper respiratory tract
21.3. Upper Respiratory Tract Diseases Caused by Microorganisms
A. Rhinitis, or the common cold
1. Signs and symptoms
2. Causative agents
a. Rhinoviruses
b. Coronaviruses
3. Pathogenesis and virulence factors
a. Penetrate mucus and attach to host cells
b. Most symptoms are due to the immune system reaction to infection
4. Transmission and epidemiology
a. Droplet contact
b. Airborne
5. Prevention
a. No vaccine
b. Best prevention is to stop transmission between hosts
6. Treatment
a. Antihistamines, decongestants, etc.
B. Sinusitis
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1. Signs and symptoms
a. Sinus infection
2. Causative agents
a. Bacteria
b. Fungi
C. Acute otitis media (ear infection)
1. Signs and symptoms
2. Causative agents
a. Streptococcus pneumoniae
b. Haemophilus influenzae
3. Transmission and epidemiology
a. Occurs as sequelae after upper respiratory tract infection
4. Prevention
a. Vaccines
i. Hib
ii. Prevnar
5. Treatment
a. “Watchful waiting” for 72 hours
b. Tubes in ears
D. Pharyngitis
1. Signs and symptoms
2. Causative agents
a. Cold viruses
b. Streptococcus pyogenes
3. Pathogenesis
a. Serious complications of strep throat include:
i. Scarlet fever
1. Scarlatina in North America
ii. Rheumatic fever
1. Heart valve damage
iii. Glomerulonephritis
iv. Necrotizing fasciitis (rare)
v. Toxic shock syndrome (rare)
4. Virulence factors
a. M protein
b. Lipoteichoic acid (LTA)
c. Cell wall polysaccharides
d. Hyaluronic acid capsule
e. Streptolysins O and S
f. Erythrogenic toxin (scarlet fever)
g. Superantigens
i. Streptolysin O and erythrogenic toxin
ii. Stimulate overly strong reactions from immune system
iii. Results in vascular injury
5. Transmission and epidemiology
6. Culture and diagnosis
a. Group A (Lancefield group of carbohydrates)
b. ß hemolytic
7. Prevention
a. Vaccine not available
8. Treatment
1-2
a. Penicillin
b. Macrolide resistance (erythromycin) in many strains of S. pyogenes
E. Diphtheria
1. Signs, symptoms, and causative organism
a. Corynebacterium diphtheriae
2. Pathogenesis and virulence factors
a. Exotoxin encoded by a bacteriophage of C. diphtheriae
b. A-B toxin
c. Exotoxin in blood can cause myocarditis and neuritis
3. Prevention and treatment
a. DTaP Vaccine
21.4. Diseases Caused by Microorganisms Affecting the Upper and Lower Respiratory Tract
A. Whooping cough
1. Signs and symptoms
a. Catarrhal stages
b. Paroxysmal stages
c. Convalescent phase
i. Secondary infections
2. Causative agent
a. Bordetella pertussis
3. Pathogenesis and virulence factors
a. Filamentous hemagglutinin (FHA)
b. Pertussis toxin
c. Tracheal cytotoxin
4. Transmission and epidemiology
a. Respiratory droplets
b. Most serious in infants
5. Culture and diagnosis
6. Prevention
a. DTaP vaccine
7. Treatment
a. Supportive care
b. Antibiotics
B. Respiratory syncytial virus infection
1. Respiratory syncytial virus (RSV) infects the respiratory tract and produces giant
multinucleated cells (syncytia)
2. Most prevalent in newborn age group
3. Causes colds in older children and adults
4. Severe disease in children 6 months of age or younger
5. Symptoms include fever, rhinitis, pharyngitis, otitis, croup (coughing, wheezing,
difficulty in breathing)
C. Influenza
1. Signs and symptoms
2. Causative agents
a. Orthomyxoviridae family of viruses
b. Influenza A, B, or C
c. Antigenic drift
d. Antigenic shift
3. Pathogenesis and virulence factors
a. Influenza virus binds to ciliated cells of the respiratory mucosa
b. Infection causes rapid shedding of cells
1-3
c. Eliminate protective ciliary clearance, causing severe inflammation and
irritation
4. Transmission and epidemiology
a. Inhalation of virus-laden aerosols
b. Transmission is facilitated by crowding and poor ventilation
c. Highly contagious; infects all age groups
5. Culture and diagnosis
a. PCR, ELISA-type assays
6. Prevention
a. Annual vaccination
7. Treatment
a. Drugs must be taken early in the infection
b. Amantadine, rimantadine, Relenza, Tamiflu
21.5. Lower Respiratory Tract Diseases Caused by Microorganisms
A. Tuberculosis
1. Signs and symptoms
a. Primary tuberculosis
b. Secondary (reactivation) tuberculosis
c. Extrapulmonary tuberculosis
2. Causative agents
a. Mycobacterium tuberculosis
b. Mycobacterium avium complex (MAC) in AIDS patients
c. Mycobacterium bovis (bovine TB) (rare)
d. Acid-fast
3. Pathogenesis and virulence factors
4. Transmission and epidemiology
a. Fine droplets of respiratory mucus suspended in air
b. Factors contributing to susceptibility include:
i. Inadequate nutrition
ii. Lung damage
iii. Poor access to medical care
iv. Debilitation of the immune system
5. Culture and diagnosis
a. Mantoux test
b. Chest x rays
c. Acid-fast staining
6. Prevention
a. Limit exposure to infectious airborne particles
b. BCG attenuated vaccine used in other countries
7. Treatment
a. Isoniazid
b. Rifampin and pyrazinamide
c. Multi-drug-resistant TB (MDRTB)
d. Extensively drug-resistant TB (XDRTB) identified in Africa in 2006
e. MAC: antibiotics to prevent this complication should be given to all patients
with AIDS
B. Pneumonia
1. Signs and symptoms
a. Starts with upper respiratory tract symptoms
b. Lung symptoms (chest pain, fever, cough, discolored sputum) follow
2. Causative agents of community acquired pneumonia
1-4
a. Streptococcus pneumonia
i. Normal biota in upper respiratory tract of 5 to 50% of healthy people
ii. Factors favoring development of disease include:
1. Old age
2. Season (winter)
3. Underlying disease (viral respiratory disease, diabetes, chronic
abuse of alchol or narcotics)
iii. Lobar pneumonia
iv. Consolidation
v. Prevent with pneumococcal polysaccharide vaccine
vi. Treat with antibiotics
b. Legionella pneumophila
i. Gram-negative bacterium with a range of shapes
ii. Causes pneumonia with a fatality rate of 3 to 30%
iii. Found in aqueous habitats
iv. Opportunistic disease in elderly people
c. Mycoplasma pneumonia
i. Lack a cell wall
ii. Irregularly shaped
iii. Atypical pneumonia transmitted by aerosol droplets (“Walking
pneumonia”)
iv. Diagnosis is by ruling out other bacteria or viral agents
d. Hantavirus
i. Symptoms, pathogenesis, and virulence factors
ii. Transmission and epidemiology
1. Airborne dust contaminated with urine, feces, or saliva of
infected rodents
iii. Treatment and prevention
1. Vaccine in development
e. SARS
i. Severe acute respiratory syndrome
ii. Caused by a coronavirus
iii. Concentrated in China and Southeast Asia
iv. Close contact (direct or droplet) required for transmission
f. Histoplasma capsulatum
i. Pathogenesis and virulence factors
ii. Transmission and epidemiology
iii. Culture and diagnosis
iv. Prevention and treatment
g. Pneumocystis (carinii) jirovecii
i. Symptoms, pathogenesis, and virulence factors
ii. Transmission and epidemiology
iii. Culture and diagnosis
iv. Prevention and treatment
3. Causative agents of nosocomial pneumonia
a. Streptococcus pneumoniae
b. Klebsiella pneumoniae
c. Polymicrobial
d. Diagnosis and culture
e. Prevention and treatment
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