Microbiology 62 [5-11

Microbiology 62: Respiratory System Infections
Most common site for infection
Pneumonia = #1 cause of death from infectious disease
Infections of Nose and Throat
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
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
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
Acute tracheobronchitis = infection or inhalation of irritants
o Viruses (rhino, corona, RSV, influenza, and adenoviruses) or bacteria (M. pneumonia,
Chlamydophila pneumoniae, Bordetella pertussis)
 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
Bronchiolotis associated with respiratory synsytial virus
Infections of the Lungs
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
Direct inhalation, aspiration, spread along mucous membrane surface, hematogenous, or direct
Defense Mechanisms of lungs
Vibrissae (hair in lungs) filter large particles
Large particles (> 10 μm) settle at abrupt change points, small particles reach terminal
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
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 –
 Predilection for very young and elderly (COPD)
o Atypical presentation = less severe, dry cough, headache
 M. pneumoniae, C. pneumoniae and legionellae
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
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
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
Other infections from Aspergillus fumigatus and CMV -> immunosuppression for organ