34 Community-Acquired and Hospital-Acquired Pneumonia Flashcards
1
Q
Epidemiology
- Pneumonia
- Pneumonia in the immunocompetent host
- Pneumonias in immunocompromised hosts
A
- Pneumonia
- Infection of the gas exchanging or alveolar compartment of the lung
- A common clinical problem that accounts for significant morbidity and mortality
- Pneumonia in the immunocompetent host
- Broadly classified as “community-acquired” or “hospital-acquired”
- The pathogens involved, empiric antibiotic therapy, and prognosis differ between the two entities.
- Pneumonias in immunocompromised hosts
- Such as individuals with Human Immunodeficiency Virus (HIV) infection, transplant recipients, and patients with neutropenia (neutrophil counts <500)
- Distinguished from community-acquired and nosocomial pneumonia, since a unique set of pathogens must be considered in immunocompromised patients
2
Q
Epidemiology:
Community-acquired pneumonia (CAP)
- Refers to…
- Generally does not include patients who have evidence for…
- Residents of nursing homes
- Prevalence
- Mortality rates
A
- Refers to…
- Pneumonia acquired in the community (as opposed to the hospital) in an immunocompetent host
- Generally does not include patients who have evidence for…
- Significant aspiration
- Bronchial obstruction
- Chronic pneumonia as caused by fungi or tuberculosis
- Residents of nursing homes
- Considered by some investigators to be residing in the community
- Others have excluded nursing home residents from studies of CAP
- Prevalence
- ~ 5 million cases of CAP a year in the U.S. alone
- Of these, ~20% require hospitalization
- 6th leading cause of death in the US
- ~ 5 million cases of CAP a year in the U.S. alone
- Mortality rates
- Vary from <5% in those not requiring hospitalization, to approximately 25% among patients requiring hospitalization
3
Q
Epidemiology:
Hospital-acqruied pneumonia (HAP)
- Refers to…
- Prevalence
- Mortality rates
A
- Refers to…
- Pneumonia that develops more than 48 hours after hospital admission
- Prevalence
- 2nd most common hospital-acquired infection
- Occurs in as many as 1% of all hospital admissions
- Mortality rates
- Significantly higher than from community-acquired pneumonia
- Approach 50% in some series
4
Q
Pathogenesis and pathology:
In the healthy state
- The respiratory tract below the vocal cords
- The upper airway (above the vocal cords, including naso- and oropharynx)
- The resident flora
- Host defense mechanisms
- Upper airway defense mechanisms
A
- The respiratory tract below the vocal cords
- Sterile, that is, free of bacteria
- The upper airway (above the vocal cords, including naso- and oropharynx)
- Normally inhabited by a host of bacteria that constitute the “normal respiratory flora” (including viridans streptococci, micrococci, Neisseria spp and Candida among others)
- The resident flora
- Thought to contribute to host defense by competing with potential pathogens for nutrients and binding sites
- Host defense mechanisms
- Have evolved to maintain sterility of the lower respiratory tract in the face of exposure to bacteria and viruses by aspiration from the upper airway and/or aerosolization from the environment
- Upper airway defense mechanisms
- Fltering via the nasal passage and oropharynx
- Sloughing of epithelial cells for clearance
- Mucociliary transport from the nasal passages
- The sneeze reflex
- Nasal secretions that contain a variety of antimicrobial substances
- Defensins (anti-microbial peptides)
- Lactoferrin
- Lysozyme
- Immunoglobulin A (IgA)
5
Q
Pathogenesis and pathology:
In the healthy state
- Defense mechanisms within the glottis
- Defense mechanisms within the trachea and conducting airways (bronchi and bronchioles)
- If microbes evade these relatively nonspecific defense mechanisms,…
- An inflammatory response initiated by the macrophage leads to…
A
- Defense mechanisms within the glottis
- Glottic closure
- The cough reflex
- Defense mechanisms within the trachea and conducting airways (bronchi and bronchioles)
- The bifurcating airway impedes direct access to the alveolar space
- Impaction of large particles on this surface defends the airspace against infection
- Once entangled in the mucus layer of the conducting airways, particles are transported via the mucociliary escalator for cough clearance or swallowed from the oropharynx
- Antimicrobial substances provide defense against microbial proliferation
- If microbes evade these relatively nonspecific defense mechanisms,…
- Other components of the lung defense system, such as immunoglobulins, alveolar macrophages, and surfactant proteins or collectins serve to thwart microbial invasion of the airspace
- An inflammatory response initiated by the macrophage leads to…
- Neutrophil recruitment from the vascular space to airway, providing a final line of defense against infection
6
Q
Pathogenesis and pathology
- Disruption of any component of these defense mechanisms predisposes to…
- Examples
- Interestingly, approximately 50% of normal individuals aspirate…
- That pneumonia is not observed more frequently consequent to the high concentration of bacteria in oral secretions speaks for…
- Hematogenous seeding of the lung
A
- Disruption of any component of these defense mechanisms predisposes to…
- Infection of the lower airway
- Examples
- The effects of tobacco smoke on ciliary function and mucociliary clearance
- Impairment of the cough reflex in the setting of neurologic impairment
- Bypassing of the upper airway via tracheostomy or endotracheal intubation
- Viral infection (particularly influenza) with its adverse affects on mucociliary clearance
- Interestingly, approximately 50% of normal individuals aspirate…
- Small amounts of oropharyngeal secretions during sleep
- That pneumonia is not observed more frequently consequent to the high concentration of bacteria in oral secretions speaks for…
- The effectiveness of normal host defense mechanisms at preventing lower airway infection (bronchitis, bronchiolitis, and pneumonia)
- Hematogenous seeding of the lung
- Occurs much less commonly than infection via aspiration or aerosolization into the tracheobronchial tree
- Can lead to the development of pneumonia
- Most often seen in patients with right-sided bacterial endocarditis due to Staphylococcus aureus
- IV drug use as risk factor
7
Q
Pathogenesis and pathology:
Aspiration pneumonitis
- General
- Occurs most often with…
- The lung injury
- Phases of aspiration
- After aspiration, the patient may develop…
- The aspirated contents
- The inflammatory response
A
- General
- An acute lung injury after inhalation of regurgitated gastric contents
- Occurs most often with…
- Altered consciousness (intoxications)
- Swallowing problems after a stroke
- The lung injury
- Depends on the pH of aspirated gastric contents
- Causes a chemical burn of the tracheobronchial tree and pulmonary parenchyma leading to inflammation
- Phases of aspiration
- 1st phase: seen within 1-2 hour due to the direct effect of acid
- 2nd pahse: after 4-6 hours during which neutrophils infiltrate into the alveoli
- After aspiration, the patient may develop…
- A fever, leucocytosis and a short-lived infiltrate on Chest X-ray
- Mimicks infectious pneumonia
- The aspirated contents
- Most often sterile (since gastric pH is so low)
- The inflammatory response
- Usually resolves within 48 hours and does not need antibiotic treatment
- If the stomach or oropharynx is heavily colonized with gram negative rods and/or the patient is at very high risk for complications, a short course of appropriate antibiotics can be considered
8
Q
Pathogenesis and pathology: Lobular pneumonia (bronchopneumonia)
- Refers to…
- Frequency
- Pathologic findings
- With bacterial pneumonia,…
- Typically, with resolution of infection,…
- Uncommonly, and with particularly virulent organisms (Staphylococcus aureus, for example),…
A
- Refers to…
- Patchy consolidation of the lung
- Frequency
- This pattern is the most common pathologic manifestation of bacterial pneumonia
- Any pathogen can lead to bronchopneumonia
- Pathologic findings
- Areas of inflammation in the bronchi
- Bronchioles
- Alveolar space within one or more lobes of the lung
- With bacterial pneumonia,…
- Neutrophils predominate
- There is a proteinaceous exudate that fills the alveolar spaces
- Typically, with resolution of infection,…
- The inflammatory process resolves
- Alveolar architecture returns to normal
- Uncommonly, and with particularly virulent organisms (Staphylococcus aureus, for example),…
- There is necrosis within the areas of lung inflammation, leading to abscess formation
9
Q
Pathogenesis and pathology:
Lobar pneumonia
- Refers to…
- Typically caused by…
- Characterized by…
- Inflammatory response
- Resolution often occurs…
A
- Refers to…
- Infection involving most or all of a lobe of the lung
- Typically caused by…
- Streptococcus pneumoniae
- Characterized by…
- Widespread inflammatory exudate in the alveolar space
- Inflammatory response
- Acute neutrophilic inflammation is typically followed by the accumulation of fibrin in the alveolar space, without destruction of the alveolar walls
- Resolution often occurs…
- Over several days, with digestion of the fibrinous exudate leading to resorption, expulsion via cough, or digestion by macrophages
- Alveolar architecture often returns to normal
10
Q
Pathogenesis and pathology:
Interstitial pneumonia
- Refers to…
- This pathologic lesion is characteristic of…
- May be seen with…
- In severe cases, there is…
- Resolution of the infection
A
- Refers to…
- Iinflammation that is largely confined to the alveolar wall
- Leukocyte infiltration and edema but no filling of the alveolar space
- This pathologic lesion is characteristic of…
- Viral infections (particularly influenza)
- May be seen with…
- “Atypical” pathogens such as Mycoplasma pneumonia
- In severe cases, there is…
- Desquamation of alveolar epithelial cells with fluid and/or blood accumulation in the alveolar space
- This may lead to filling of the alveolar space (consolidation), or the formation of hyaline membranes
- Resolution of the infection
- As with broncho-and lobar pneumonia, is typically followed by restoration of normal lung structure and function
- Less commonly, interstitial inflammation leads to scarring in the form of alveolar fibrosis
11
Q
Community-acquired pneumonia (CAP):
The most common pathogens associated with each category
- Outpatient, no co-morbidities
- Outpatient, co-morbidity (COPD, diabetes, renal or congestive heart failure, malignancy)
- Hospitalized
- Hospitalized, severe disease
A
- Outpatient, no co-morbidities
- Streptococcus pneumoniae
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Viruses (adenovirus, influenza, RSV, metapneumovirus, and others)
- Haemophilus influenza
- Legionella
- Outpatient, co-morbidity (COPD, diabetes, renal or congestive heart failure, malignancy)
- Streptococcus pneumoniae
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Viruses (adenovirus, influenza, RSV, metapneumovirus, and others)
- Haemophilus influenza
- Legionella
- Hospitalized
- Streptococcus pneumoniae
- Haemophilus influenza
- Polymicrobial
- Viruses (adenovirus, influenza, RSV, metapneumovirus, and others)
- Legionella
- Hospitalized, severe disease
- Streptococcus pneumoniae
- Viruses (adenovirus, influenza, RSV, metapneumovirus, and others)
- Legionella
- Pseudomonas aeruginosa and other Gram-negative bacilli
- Staphylococcus aureus
12
Q
Community-acquired pneumonia (CAP):
Two important points need to be made with regard to the etiology of CAP
- Identifying pathogens responsible for CAP
- Prominent causative organisms
- “Atypical” organisms
- Pseudomonas aeruginosa
A
- No pathogen responsible for community-acquired pneumonia is identified in up to 50% of patients, despite earnest attempts to identify an organism
- In every category (outpatient, no comorbidities; outpatient, comorbidities; hospitalized; hospitalized, severe disease), Streptococcus pneumoniae and “atypical” organisms (Mycoplasma pneumoniae, Chlamydophilia pneumoniae and Legionella) feature prominently in the list of causative organisms
- Therefore, all empiric treatment regimens for CAP must cover both Streptococcus pneumoniae and the “atypical” organisms
-
“Atypical” organisms
- Bacteria which are not visualized on Gram stain and will not readily grow on agar plates routinely used to culture bacteria
- Examples of these bacteria include Mycoplasma pneumoniae, Chlamydiophilia pneumoniae and Legionella species
- Pseudomonas aeruginosa
- Rarely a cause of CAP
- Only needs to be covered with specific antipseudomonal antibiotic therapy in certain patients admitted to intensive care units (ICUs) with CAP
- Risk factors for Pseudomonas infection
- Severe structural lung disease (eg, bronchiectasis)
- Recent antibiotic therapy
- Recent stay in hospital (especially in the ICU)
13
Q
Hospital-acquired pneumonia (HAP):
Etiology
- Early-onset VAP
- Occurs…
- Associated with…
- Key pathogens
- Late-onset VAP
- Due to…
- Typical pathogens
- Typified by…
- Non-ventilator-associated hospital-acquired pneumonia
- General
- Common pathogens
A
- Early-onset VAP
- Occurs within the first week of mechanical ventilation
- Associated with upper respiratory flora
- Key pathogens: Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus
- Late-onset VAP
- Due to micro-aspiration of the more resistant bacteria replacing normal upper respiratory flora due to cross contamination and antibiotic pressures in the ICU
- Typical pathogens: Pseudomonas aeruginosa, Staphylococcus aureus (typically methicillin resistant), and enteric Gram negative bacilli (Klebsiella pneumoniae, Enterobacter cloacae etc)
- Typified by antibiotic resistant organisms making treatment difficult
- Non-ventilator-associated hospital-acquired pneumonia
- Heterogeneous condition that in many cases may be associated with aspiration
- Common pathogens: enteric Gram negative bacilli (Escherichia coli, Klebsiella, Proteus mirabilis, Serratia marcescens), sometimes anaerobic Gram negative bacilli, Haemophilus influenzae, Staphylococcus aureus and occasionally Streptococcus pneumoniae
14
Q
Symptoms and signs
- Typical findings are often absent in…
- Classical symptoms of pneumonia
- Typical bacterial pneumonia
- Physical findings
- Chest exam
A
- Typical findings are often absent in…
- The elderly
- Classical symptoms of pneumonia
- Cough, fever, and shortness of breath
- Typical bacterial pneumonia
- Begins with chills or rigors
- Followed by fever, cough productive of purulent or rusty sputum, and shortness of breath
- Chest pain may occur in up to a third of patients, and is often pleuritic in character due to pleural inflammation.
- Physical findings
- Fever (present in most patients but less reliable as a finding in the elderly), tachypnea, and tachycardia
- Chest exam
- Crackles over the involved area of lung
- With more extensive disease, there may be findings of consolidation (dullness to percussion, tubular or bronchial breath sounds, and/or egophony and increased tactile fremitus)
- In contrast, pleural effusion or empyema (infection of the pleural space) associated with pneumonia that involves an area of lung adjacent to the pleural surface, should be suspected when there is dullness to percussion with diminished breath sounds and decreased tactile fremitus
15
Q
Symptoms and signs
- Ventilated or neurologically impaired patients
- The diagnosis of hospital-acquired pneumonia
- Fever
- Clinical findings of crackles or those consistent with pleural effusions
- Ventilated patients
- Spontaneous expectoration of sputum
- Clues to pneumonia in this patient population
A
- Ventilated or neurologically impaired patients
- May not be able to provide any history
- The diagnosis of hospital-acquired pneumonia
- May be difficult
- Fever
- Typical in patients with pneumonia
- Seriously ill patients may have multiple potential causes for fever
- Clinical findings of crackles or those consistent with pleural effusions
- May have etiologies other than pneumonia in such patients
- Ventilated patients
- Spontaneous expectoration of sputum is not possible
- Clues to pneumonia in this patient population
- Increased need for suctioning
- Purulent respiratory secretions
- Increased oxygen requirements