L12. Lower Respiratory Tract Infections Flashcards
What are the 6 major syndromes that occur in the lower respiratory tract?
- Acute Bronchitis
- Acute Exacerbations of Chronic Bronchitis
- Bronchiolitis
- Pneumonia
- Lung Abscess
- Empyema
What is the most common pathogenesis of acute bronchitis?
Usually an URT that has spread down the epithelia causing infection of the bronchi.
Thus is often starts with rhinitis, sore throat, hoarseness and then bronchitis.
What is meant by acute exacerbation of chronic bronchitis? How are they caused?
Chronic Bronchitis leaves the LRT relatively damaged and susceptible to secondary bacterial infection. The acute exacerbations cause small bouts of fever, productive sputum (purulent and blood stained)
What is the most common example of chronic bronchitis?
Chronic Obstruction Pulmonary Disease
What are the usual causative pathogens causing acute exacerbations of chronic bronchitis?
Usually by non-pathogenic pathogens
Pneumoccoi (less virulent)
H.influenzae (non-typable)
What is the major pathogenic cause of Bronchiolitis?
RSV
Why is bronchiolitis more common in infants?
It is believed that children acquire preformed antibodies from their mothers. However in infancy, the immune system isn’t matured enough to form a matured response.
What are the three types of pneumonia?
- Typical (lobar)
- Atypical (diffuse)
- Other
What are the major pathogenic organisms that cause acute bacterial pneumonia?
Pneumococci (80% community acquired) H.influenzae Staphylcocci Klebsiella Legionella TB Chlamyophilia
What is the pathogenesis of acute pneumonia?
Aspiration of microbiota into the alveoli where they replicate and cause inflammation
What are the characteristics of typical pneumonia? What is another name for it?
Lobar Pneumonia
Restricted to one lobe of the lung with subsequent inflammation in only that area (spreading)
What is special about the Chlaymidiophilia pneumoniae bacteria?
Have specific life cycles
Replicating form intracellularly forming inclusion bodies until their burst out and kill the cell in the process
Non-replicating form during extracellular (infectious) form
What are the major pathogenic causes of atypical pneumonia?
Mycoplasma Chlamydia M.catarrhalis influenza RSV adenovirus
What is the pathogenesis (and symptoms) of atypical pneumonia?
Gradual development with cough (less productive, less purulent) with dramatic change in CXR - interstitial tissue inflammation
What are special about mycoplasma bacteria?
have no cell wall (no fixed shapes or sizes) and are important pathogens
What bacteria aspirated in the birthing process is the causative organism to atypical pneumonia?
Chlamydia
Another group of pathogens [3] cause other types of pneumonia. What are they?
FUNGI
Histoplasma, Aspergillus, Pneumocystis
How are lung abscesses formed?
Often are remnants that persist after pneumonia is resolved.
What causative organisms lead to lung abscess formation?
Caused by mixed anaerobes including as well as staphylcoccus and Klebsiella
Why is empyema?
Collection of pus in the pleural cavity
What is the major pathogenic cause of empyema?
Complication of penumonia
penetrating chest trauma
Eosophageal rupture
Inoculation of the pleural cavity after thoracentesis or chest tube placement
What 4 factors must be considered when clinically diagnosing patients with LRTIs
- Community vs. hospital acquired
- Severity index
- Underlying illnesses
- Other risk factors (occupation, travel, homelessness)
What types and considerations should be made when deciding what kind of sample should be taken for a lab diagnosis of LRTI?
- Properly collect a sputum sample from deep chest
- Transtracheal aspirate (not widely used in Aus.)
- Aspiration: trachemostomy, endotracehal tube via endoscope
- Pleural tap
- Lung Biopsy (needle or open)
- Blood culture and serology
What are we looking for (and not looking for) when looking at gram stains of sputum collections?
Looking for pus: neutrophils and inflammatory cells.
Not looking for squamous epithelium: suggests contamination with mouth (URT microbiota)
Gram positive cocci: pneumococcus in atypical pneumonia
For what bacteria is it important to do serological diagnoses for? Why is this?
Mycoplasma pneumoniae
Legionella pneumophilia
Chamydiophilia and Chlamydia
Coxiella burneti
They are difficult to culture
Why are mouth/throat swabs often useless in diagnosing bacterial pneumonia?
Because mouth swabs test for URT bacteria. It is often the URT microbiota that is the causative organism of the LRT and thus you are unable to decipher which one is the cause.
Are mouth/throat swabs relevant to diagnosing viral LRT?
Yes because viruses rarely colonise the RT. Eg. RSV found in the throat is often a good indication of primary infection and is indicative of possible bronchiolitis in the LRT.
What is the process of specific antigen detection in aspirate and/or serological tests?
Draw blood from the patient or draw fluid and direct immunofluorescence:
Antigen detection is run against common viruses (the most common circulating viruses of the time)
What circumstances would it be important to make a specific diagnosis? [3]
- Helps prescribe appropriate antibiotics (whether to even use them)
- “Must Know” infections: outbreaks, public health issues, bioterrorism
- “Should Know” infections: for antibiotic resistant bacteria and Gram Negative Rods (inherently resistant)
What is the current gold-standard treatment for pneumonia?
Penicillin G/amoxicillin + Doxycycline/macrolide
Penicillin: pneumococcus (most common cause)
Tetracycline: Other causes that are normally penicillin resistant
Treatment for pneumonia is modified once a specific diagnosis is made (if it is made). What impacts on what changes are made?
Based in the severity of the pneumonia
Specific risk factors
The specific causative agent (resistance)
In meningitis, penicillin and tetracyclines are antagonistic drugs. Why is this not the case for pneumonia treatment?
This is because treatment for meningitis requires the drugs to cross the blood brain barrier. And penicillin only does so in small amounts (not enough to counter the bactericidal effects of tetracycline)
In pneumonia, there is no limit on penicillin accessing the target (lungs) and hence there is no antagonism.
What vaccines are available for the prevention of pneumonia? [3]
- Influenza Vaccines
- Pneumococcal vaccines
- Specialised (for people more likely to be in contact with causative organisms)
