lower respiratory tract Flashcards
Lower Respiratory Tract (LRT) consists of
The LRT Consists of the following > Trachea > Bronchi > Bronchioles > Lung Alveoli
LRT bacteria
Typically, the lower respiratory tract is sterile
Areas below the larynx do not contain “normal flora”
Exceptions:
> Patients with
- Chronic Pulmonary Disease
- Endotracheal Tubes
- Tracheostomies
LRT infections usually occur when infecting organisms reach the
lower airways or pulmonary parenchyma via bypassing the
mechanical and other nonspecific barriers of the URT
Infections may result from
- inhalation of infectious aerosols
- aspiration of oral or gastric contents
- hematogenous spread
LRT Progression of viral
In order for a LRT infection to establish itself, a series of host
defenses must be overcome
> Different sequence of events for respiratory viruses as
opposed to bacterial pathogens
Progression of viral pathogens
> Involves spread among adjacent cells and distant inoculation
of susceptible cells by aspiration of infectious secretions
> To a lesser extent, hematogenous transmission of the virus
Lung infections by bacterial pathogens occur via direct
inoculation of organisms through aspiration from the URT
Bronchitis
> Infection and inflammation of the bronchi without
involvement of the lung parenchyma (pneumonia)
Peak season is the winter months
- Coincides with the period of peak incidence of infections
Bronchiolitis
> Infection and inflammation of the smaller bronchioles
> Most common LRT infection in children younger than 2 years
BRONCHITIS AND BRONCHIOLITIS causes
> During seasons when influenza is epidemic in the community, it is
the most common cause of acute bronchitis in the general population
During non-epidemic periods, viral pathogens include
- Rhinovirus
- Coronavirus
- Human Metapneumovirus (hMPV)
- Parainfluenza Virus
BRONCHITIS AND BRONCHIOLITIS Non-viral respiratory tract pathogens
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Bordetella pertussis
Predominate cause of bronchiolitis
RSV - Respiratory Syncytial Virus
BRONCHITIS AND BRONCHIOLITIS Pathogensis
> Evidence almost always exists of an antecedent or coexistent
URT infection in patients with acute bronchitis
- Begins with fever and cough
- Destruction of respiratory epithelium varies with pathogen present
- Infection and damage to the airway
- Inflammatory response, necrotic debris, and edema cause
symptoms
BRONCHITIS AND BRONCHIOLITIS
Clinical Manifestations
> Chronic Bronchitis - requires 3 months of symptoms for at least 2 years
- Linked to long-term cigarette smoking leading to worsening of symptoms
Acute Bronchitis - from an infectious process
Acute Bronchiolitis
- Infectious disease of infants
- Usually from RSV
-Wheezing, respiratory distress and air trapping
BRONCHITIS AND BRONCHIOLITIS
Complications
> Secondary Bacterial Infections
- Bacterial bronchitis or pneumonia
- Example pathogens - S. pneumonia, H. influenzae, M. catarrhalis
BRONCHITIS AND BRONCHIOLITIS Diagnosis
> Based on history and physical examination
Secondary infections usually easy to obtain from purulent sputum
RSV PCR testing may be done for infection control purposes during outbreaks
BRONCHITIS AND BRONCHIOLITIS treatment
> Mainly control symptoms
> Antibiotics in select cases
INFLUENZA
Epidemiology
> Late fall and early winter and persist into the spring; pandemics can occur
outside of typical season
Influenza causes
> Influenza A and B
Influenza A - Categorized into subtypes on the basis of two surface antigens
- Hemagglutinin (H)
- Neuraminidase (N)
Influenza B - Categorized into lineages
influenza pathogenesis
> Antigenic shift - Production of new virus - May prevent detection with kits in use > Pandemics in 1957 and 1968 - Caused by genetic re-assortment between influenza viruses from humans and birds > Pandemic in 2009 - H1N1 - Caused of re-assortment of genetic elements of human, swine and avian strains
Influenza clinical manifestation
> Fever, muscle pain and fatigue
influenza complications
> Populations at increased risk for severe disease
-Young children, pregnant women, patients with underlying health
conditions
Secondary bacterial pneumonias
- S. pneumoniae, S. aureus (including community-associated strains of
MRSA) and H. influenzae
influenza diagnosis
> In the setting of an influenza outbreak, acute febrile
respiratory illnesses can be diagnosed with relative certainty by
clinical criteria alone
Detection of virus, viral antigen, or viral nucleic acid
- Pharyngeal swabs, nasal washes, sputum or
bronchoalveolar lavage/washings
influenza treatment & prevention
> Antiviral drugs
- Neuraminidase inhibitors and M2 inhibitors
- Choice of treatment depends on the susceptibility of
currently circulating influenza strains along with patient
characteristics
prevention: Annual vaccination in the fall of each year (Flu Vaccine)
emerging viral RT infections
Highly pathogenic avian influenza (HPAI)
> H5N1 avian influenza
> H7N9 avian in origin
Pandemic H1N1 influenza A and other swine influenza variants
> H1N1 influenza A pandemic
> H3N2 influenza A
Severe Acute Respiratory Syndrome (SARS) caused by a coronavirus
(SARS-CoV)
Middle East Respiratory Syndrome (MERS) caused by a coronavirus
(MERS-CoV)
The Novel Coronavirus known as SARS-CoV-2 that caused coronavirus
disease (COVID-19) – The Current Pandemic!
Adenovirus Infections
- Re-emergence in military and civilian populations
- Serotypes 4 and 7, group B serotype 14
acute pneumonia
Distinction between acute bronchitis and acute pneumonia
may be subtle
> Depends on the extent of involvement of the LRT with the
infectious process
> Patients who have bronchitis do not exhibit the physical,
radiographic, and pathologic findings of pulmonary
parenchymal involvement outside of the airways - this type of
involvement with the infectious process defines pneumonia
community aquired pneumonia ( CAP) definition
> The onset of symptoms is in the community or within the first two days
after admission to the hospital
CAP epidemiology
> CAP is one of the most common infections encountered in clinical practice
Leading cause of death from infection in persons over the age of 65
Vaccination against S. pneumonia (Most common bacterial pathogen in
children and adults)
- Resulted in decreases in invasive pneumococcal disease
- Despite advances in diagnostics and therapeutics in recent years,
mortality rates have remained unacceptably high
CAP causes
> Linked to viral infections during winter
Summer months - atypical pneumonia
Most cases are older adults or patients with underlying disease
Example Causes
RSV: children - especially in infants
Influenzae - most common virus isolated in adults
S. pneumoniae, Hib, M. pneumonia - adults
M. pneumoniae and Legionella pneumophila - atypical
pneumonia
CAP pathogenesis
> In most cases, defense mechanisms of the lung, including
the ciliated epithelial cells and innate immune system
phagocytic cells can clear aspirated bacteria before infection
is established
LRT infections can occur when the
- bacteria involved are particularly virulent
- high inoculation of microorganisms
- immune system is compromised
CAP clinical manifestations
> Varies with the age and immunologic status of the host
Most infected patients experience
- Fever associated with chills
- Cough with blood-tinged, purulent sputum
- Left shift WBC count (increased WBC and immature neutrophils)
- Localized area of the lung involvement (lobar consolidation)
that may be associated with hypoxia or reduced oxygenation
CAP complications
> Varies with the age and immunologic status of the host
Most infected patients experience
- Fever associated with chills
- Cough with blood-tinged, purulent sputum
- Left shift WBC count (increased WBC and immature neutrophils)
- Localized area of the lung involvement (lobar consolidation)
that may be associated with hypoxia or reduced oxygenation
> Respiratory Failure
- Including the need for mechanical ventilation
Acute Respiratory Distress Syndrome (ARDS)
Septic shock with multisystem organ failure
Encephalitis may occur - In a minority of atypical
pneumonia cases
- Inflammation of the brain
CAP lab diagnosis ( outpatients & hospitalized patients)
> Outpatients with mild disease – diagnostic tests not general
> Hospitalized patients
- Blood cultures and sputum specimens collected
- Molecular tests such as PCR
- Antigen tests
- Direct examination of sputum
10 or fewer squamous epithelial cells/LPF
CAP lab diagnosis ( tracheal needle aspiration )
- Rarely used due to invasiveness, risk of complications and patient
unacceptability
CAP lab diagnosis ( bronchoscopic methods)
- For patients who require mechanical ventilation
- Also used in cases of refractory or recurrent pneumonia when
empiric therapy is in doubt
Note: Legionella cases challenging to diagnose from sputum or
bronchial aspirates
(Requires special media, Organisms do not stain well with Gram stain)
CAP lab diagnosis ( molecular diagnostic tools )
> Molecular diagnostic tools - PCR assays
- Have been used to identify pathogens in cases otherwise
negative for culture
- Have been used to provide rapid test results to allow better
targeting of therapy
- Sensitivities have significantly improved
- Specificity problems do exist and as such results must be
interpreted in context (True pathogen or asymptomatic
colonization?)
CAP lab diagnosis ( pneumococal pneumonia )
- S. pneumoniae
- α-Hemolytic colonies on blood agar
- Biochemical tests - Bile solubility and optochin sensitivity
(Used to distinguish S. pneumoniae from other streptococci) - Cultures from blood and pleural fluid may also contain the S.
Pneumonia and can be used for diagnosis
CAP treatment
> Treatment varies with each patient and a number of
factors must be taken into consideration
The potential of drug-resistant pneumococcal infection
must be considered
In cases of comorbidities or recent antimicrobial use,
among other risk factors:
- Respiratory fluoroquinolone alone or,
- β-lactam antibiotic plus a macrolide is recommended
HOSPITAL ACQUIRED (HAP) AND
VENTILATOR ASSOCIATED PNEUMONIA
(VAP)
HAP - Pneumonia acquired 48 hours or more after hospital
admission and not associated with mechanical ventilation
VAP - Pneumonia episode diagnosed at least 48 hours after
airway intubation and initiation of mechanical ventilation
Nosocomial - Originating in a hospital/hospital environment
HAP
HAP AND VAP
Epidemiology
> VAP occurs in ~20% of patients requiring mechanical
ventilation more than 48 hours
HAP & VAP causes
> Greater risk of multidrug-resistant pathogens (MDRs)
Ex. Pseudomonas aeruginosa Klebsiella pneumoniae,
Acinetobacter baumannii MRSA
Klebsiella spp. Enterobacter spp.
E. coli
HAP & VAP pathogenesis
> Acquired from patient’s own respiratory flora, GI tract or hospital
flora
- Aspiration of bacteria
Intubation of the lower airway
- Bypasses the normal mechanical defenses provided by the glottis
and cough reflex
Nasogastric intubation
- Interferes with glottic function
- Increased reflux of gastric secretions into the oropharynx
HAP & VAP clinical manifestations
> A new or persistent infiltrate on chest imaging that is accompanied by at least two of the following - Fever - Elevated or depressed WBC count - Production of purulent sputum
HAP & VAP complications
> Rapidly progressing pneumonia requires ventilators due to overwhelming
infection or lung injury
Bacteremia
- If gram-negative, can lead to shock
HAP & VAP laboratory diagnosis
> Same principles for microbiological diagnosis apply as discussed for
CAP
Noninvasive semi-quantitative sampling for diagnosis of the
potential pathogen (ie. Expectorated sputum, endotracheal aspiration)
Must be a quality specimen that is not contaminated from the
oropharynx
Culture - SBA, MAC, and CHOC agar
- If no contamination, can perform anaerobic cultures
Blood Cultures can be used in severe cases and/or sepsis
Legionella culture included if Legionella spp. is a possible cause
HAP & VAP treatment
> Antibiotic treatment with modification based on culture data
and clinical response
Consider institution’s antibiogram and patient’s previous
resistance patterns
VAP bundles/measures
- Elevating the head of the bed to prevent aspiration
- Weaning sedation daily to decrease time on the ventilator and
prevent complete suppression of the protective cough reflex
- Oral care with chlorhexidine to decrease oral colonization
Empyema
Collection of purulent fluid in the pleural cavity
Empyema epidemiology
> Most empyemas occur in association with concurrent
community-acquired acute pneumonia
Risk factors
- Advanced or very young age, male gender, debilitation,
comorbid disease(s), and longer duration of
symptoms prior to receiving appropriate therapy
- Increased incidence in children noted after seasonal
and pandemic influenza epidemics
Empyema causes
> Most common pathogen isolated from empyemas in children
- S. pneumonia
Other common causes in patients with CAP
- S. pyogenes
- Other streptococcal species
- S. aureus
Main cause in hospitalized patients empyemas
- aerobic gram-negative bacilli
Empyema pathogenesis
> May complicate chest surgery or chest trauma
May limit the motion and function of the lung
Resistant to antimicrobials - due to low blood flow and low pH
in the area
Empyema clinical manifestations
> Collection of fluid in lung and chest wall
Fever, chills, night sweats
Sepsis may develop
Empyema complications
> Persistent empyema is difficult to eliminate.
Unresolved sepsis
Thick encapsulation of the lung, resulting in loss of function
Empyema lab diagnosis
> Aspirates of pleural fluid
Evacuate the air in syringe to help isolate anaerobes
Save aliquot for special studies if needed
Empyema treatment
> Drainage of infected fluid
> Treatment with antimicrobials
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS
Bacterial pneumonias usually resolve completely over a
period of weeks
On occasion, resolution is delayed
> Radiographic lung abnormalities that persist beyond the
improvement of symptoms
Necrotizing processes in the lung may occur
Some pneumonias are inherently slow in progression and
chronic in nature
> Mycobacterial and fungal infections of the lung
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS causes
> Mycobacteria
- In immunocompetent patients
Nontuberculous mycobacteria (NTM)
- Immunocompromised and socially disadvantaged
- M. avium complex, M. kansasii, and M. chelonae/abscessus
Opportunistic fungal pathogens
- Aspergillus, Cryptococcus, Histoplasma capsulatum,
Blastomyces dermatitidis, and Coccidioides immitis
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS
Pathogenesis
> Granulomatous response in the lung
Cell-Mediated Immunity (CMI) is involved in both protective
and destructive aspects of these illnesses
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS
clinical manifestations
Symptoms vary by responsible microorganism present
> Less acute symptoms appear gradually
> Localized or disseminated infection
> Immunocompromised patients may have severe infections
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS
complications
> Respiratory insufficiency
Lung fibrosis
Dissemination to other vital organs
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS
lab diagnosis
> Mycobacteria require specific culture media and have ong growth times
Proper respiratory isolation - Highly infectious
Specimen collection
- Sputum
- Bronchoscopic specimens
- Lung biopsies
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS
diagnosis ( direct examination & others)
> Direct Examination - Acid-fast or other special stains (i.e., Ziehl-Neelsen) - Fungal agent preps > Other Tests - Nucleic acid testing - Serologic tests - Skin tests - Purified protein derivative (PPD) for tuberculosis - Interferon-gamma release assays (IGRA)
TUBERCULOSIS AND OTHER CHRONIC
PNEUMONIAS
treatment
> Pansusceptible Tuberculosis
- Isoniazid (INH), rifampin, pyrazinamide, and ethambutol for an initial
2 months, followed by isoniazid and rifampin for an additional 4 months
Multidrug-Resistant Tuberculosis
- Treatment based on antibiotic susceptibility testing results and
consultation with an expert in tuberculosis therapy
Fungal Infections
- IV amphotericin B preparation and then followed with an oral agent for
prolonged treatment (12 to 24 months)
ASPIRATION PNEUMONIA
Aspiration - occurs when gastric or oropharyngeal contents
are inhaled into the larynx or LRT
ASPIRATION PNEUMONIA
epidemiology
> Associated with frequency of aspiration, material aspirated
and host defenses
Increased risk associated with periodontal disease
Occurs in children and adults and more common in
hospitalized patients
ASPIRATION PNEUMONIA
causes
> Community Acquired
- S. pneumoniae, H. influenzae, Staphylococci and Enterobacteriaceae
Nosocomial Acquired
- Predominantly gram-negative pathogens including P. aeruginosa
Possible anaerobic causes
- Bacteroides spp., Prevotella, Peptostreptococci, Fusobacterium spp.
ASPIRATION PNEUMONIA
pathogenesis
> Factors of disease
- Frequency of aspiration
- Quality and quantity of material aspirated
- Host defenses - Underlying disease
Immunocompromised patients
- Increased risk of infection after aspiration of a bacterial inoculum
Chemical aspiration
- Occurs when inhaled gastric acid causes injury
- Severe inflammatory response, edema, decreased lung capacity, hypoxia
ASPIRATION PNEUMONIA
clinical manifestations
> Aspiration event with increased coughing, wheezing, hypoxia
Abscesses have a longer history of illness (weeks) than acute
pneumonia
Putrid sputum and halitosis (bad breath) - Due to anaerobes
ASPIRATION PNEUMONIA
complications
> If treatment fails - Progression to a necrotizing pneumonia and lung
abscess possible
Patients with lung abscesses usually have a longer history of illness,
more subtle onset of symptoms, have a putrid sputum and complain of bad
breath
ASPIRATION PNEUMONIA diagnosis
> Specimen collection methods are similar to those for CAP and
nosocomial infections
Difficulty lies in determining whether or not therapy is warranted
ASPIRATION PNEUMONIA
treatment
> Broad-spectrum antibiotics that provide coverage for aerobic,
gram-negative organisms
Anaerobic bacteria should be empirically treated if implicated`
