Microbiology 62: Respiratory System Infections
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Most common site for infection
Pneumonia = #1 cause of death from infectious disease
Infections of Nose and Throat
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Group A streptococcal pharyngitis = in school children in winter
o Fever, tonsillar exudates, tender cervical adenopathy increase likelihood
o Conjunctivitis, cough, coryza, diarrhea = decrease likelihood
o Complications = peritonsillar and retropharyngeal abscesses, otitis media, sinusitis,
pneumonia, acute glomerulonephritis, and rheumatic fever
Rhinoviruses, adenoviruses (conjunctivitis), coronaviruses, influenza viruses and parainfluenza
viruses may cause pharyngitis
o Epstein-Barr virus common in adolescents/young adults
o Enteroviruses (group A coxsackieviruses) -> herpangina (small vesicles in throat)
Chlamydophila pneumoniae, Arcanobacterium haemolyticum, Mycoplasma pneumonia -> other
causes of pharyngitis
Common cold from viral infection of nasopharynx
o 40-50% of colds caused by rhinovirus group
o Coronaviruses next common group
Infections of Epiglottis
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Clinical: trouble breathing, nasal flaring, drooling, fever
Nafcillin effective against influenza B
Acute epiglottitis = supraglottitis (URI), frequently 2-7 y.o from influenza B
o Universal immunization against influenza B
o In adults, S. pneumoniae and group A streptrococci more frequent causes
Radiograph of lateral neck shows enlarged epiglottis (secure airway with endotracheal tube)
Infections of Larynx and Trachea
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Larangotracheitis = croup -> sudden onset of barking cough and difficult respiration
o Viral URI (parainfluenza viruses 1-3) or rarely S. aureus, runny nose, hoarseness (in
adults), cough
o Mucous membrane edema -> narrows (esp inspiration = inspiratory stridor)
o Self0limited resolving after 5-7 days
o Provide oxygen, epinephrine, have child stand in steam room
Infections of Large Bronchi
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Acute tracheobronchitis = infection or inhalation of irritants
o Viruses (rhino, corona, RSV, influenza, and adenoviruses) or bacteria (M. pneumonia,
Chlamydophila pneumoniae, Bordetella pertussis)
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 B. pertussis -> whooping cough
Cough, myalgias, headache made worse by coughing, substernal chest pain, high fever
COPD -> chronic bronchitis -> acute exacerbation of chronic bronchitis (AECB)
 ↑ cough and sputum production, sputum purulence, and SOB increase
likelihood of bacterial infection
 Treat with antibiotics against H. influenzae, M. catarrhalis and S. pneumoniae
Infections of Bronchioles
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Bronchiolotis associated with respiratory synsytial virus
Infections of the Lungs
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Acute pneumonia = sudden onset, progression of symptoms in few days
o Community-acquired = person-to-person (airborne) or animal/environmental reservoirs
(airborne or insect vectors)
 Pneumocystis carnii -> infect immunocompromised patients
o Hospital-acquired (nosocomial)
Subacute or chronic pneumonia = tuberculosis, fungal pneumonia, anaerobic lung abscess
Entry and Spread
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Direct inhalation, aspiration, spread along mucous membrane surface, hematogenous, or direct
penetration
Defense Mechanisms of lungs
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Vibrissae (hair in lungs) filter large particles
Large particles (> 10 μm) settle at abrupt change points, small particles reach terminal
bronchioles/alveoli
o Endotracheal tubes predispose to pneumonia
Epithelial cells covered with cilia containing lysozyme, lactoferrin, secretory IgA antibodies
o Impaired cilia -> bronchiectasis (permanent dilation of small airways)
Alveoli contain IgA antibodies, complement, and macrophages
Acute Pneumonias
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Community-Acquired Pneumonia (CAP) = fever, cough, chest pain (pleuritic), SOB, rapid
respiration, cyanosis, crackles/rales
o Typical presentation = high fever, shaking chills, chest pain, lobar consolidation
 S. pneumoniae most common cause, H. influenzae, S. aureus and other Gram –
bacteria
 Predilection for very young and elderly (COPD)
o Atypical presentation = less severe, dry cough, headache
 M. pneumoniae, C. pneumoniae and legionellae
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Alcoholics increase risk for S. pneumoniae, Klebsiella pneumonia, S. aureus
Nursing home, immunocompromised, and lung disease increase risk for Pseudomonas
aeruginosa (Gram- enteric) and S. aureus
o Chlamydia psittaci -> disease in birds -> psittacosis (parrot fever)
o Coxiella brunetii -> farm animals -> Q fever
o Legionella pneumphila -> contaminated water -> Legionnaire disease
o <2 y agent usually virus (RSV, influenza, parainfluenza, adenoviruses)
o Diagnostic finding (!) = infiltrate
 Focal lobar consildation with S. pneumoniae, K. pneumoniae, aspiration
 Diffuse interstitial infiltrates with M. pneumoniae, C. pneumoniae, P. carinii
 Cavitate -> S. aureus, Mycobacterium tuberculosis
o Risk factors for drug resistant S. pneumoniae (DRSP) = recent respiratory infection,
antimicrobial use, advanced age, immunocompromised or high risk area
Hospital-Acquired Pneumonia (HAP) = new parenchymal lung infection 48+ hours after
admission to hospital
o Fever, cough, purulent (green) sputum production, SOB, pleuritic chest pain,
tachycardia, tachypnea, tactile fremitus and dullness to percussion
o Intubation -> ventilator-associated pneumonia (VAP)
o Enteric Gram negative bacteria and S. aureus typically
 Enterobacteriaceae, K. pneumonia, Proteus species, E. coli
 Prolonged hospitalization => P. aeruginosa and Acinetobacter species
o Therapy based on likelihood of infection with multidrug-resistant (MDR) pathogens
 Risk factors = antimicrobial therapy (90 days), 5+ day hospitalization, high MDR
organisms around, immunosuppression, dialysis
 Treat with broad-spectrum antibiotics
Subacute Pneumonias
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Lung abscess from gross aspiration of oropharyngeal/gastric contents -> polymicrobial infection
o Anaerobes and microaerophilic organisms from mouth
o S. aureus, K pneumoniae, mycobacteria, and others too
o Fungi -> Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis,
Cryptococcus neoformans
o Clinical = fever, foul-smelling breath, amphoric breath sounds, lung cavity
Pneumonia in the Immunocompromised Patient
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Usually rarely cause infection in normal individuals
P. carinii -> HIV pts, CD4 lymphocyte < 200
Low-grade fever, cough, fatigue, diffuse bilateral infiltrate, treat with trimethoprim and
sulfamethoxazole
Other infections from Aspergillus fumigatus and CMV -> immunosuppression for organ
transplant