Pneumonia (infectious) Flashcards
In this lecture, pneumonia refers to…
Infection of the lung by a microbe, typically involving the alveolar space and parenchyma.
How is pneumonia typically diagnosed?
CXR findings and clinically compatible syndrome (set of symptoms)
How can pneumonia be classified (4)
- Community acquired (CAP) vs Hospital acquired (HAP)
* This is the most commonly used distinction - Organisms
* Bacterial, viral, typical vs atypical pathogens - Pathogenesis
* Aspiration, ventilator-associated - Anatomic distribution
* Lobar vs multifocal bronchopneumonia vs interstitial
What is the most common infectious cause of death in North America?
Pneumonia
What is the most important cause of death in children under 5 in developing countries?
Pneumonia
What are the possible bacterial sources of pneumonia?
Usually, our lungs should be relatively microbe-free. However, bacteria can reach the lungs by…
* inhalation (bacteria and virus)
* aspiration of oropharyngeal contents (bacteria)
* direct extension (virus and bacteria travel down the airways and affect the alveolar spaces)
* hematogenous spread (bacteria)
* exogenous contamination (because alveolar wall is disrupted by trauma - eg. catheter insertion)
Why is it that the defences that usually prevent us from developing an infection fail and lead to pneumonia?
- Defect on host defences
- Overwhelming bacterial inoculum (eg. in the case of aspiration)
- Highly virulent microorganism
What are the host defences that protect our lungs from microorganisms?
- Nasopharynx, vocal cords and OP barrier
* Mucus and nose hairs trap particles
* Reflex for glottis closure when eating (prevents aspiration of food) - Mucociliary escalator
* On the surface of the respiratory epithelium, mucus traps particles and is moved upwards to clear bacteria and other foreign agents - Lung immune cells
* Macrophages in the alveolar space digest foreign agents and activated the immune system
In what conditions are the immune defences of our airways/lungs compromised?
- Disruption of glottis reflex, aspiration, abnormal OP
- Ciliary dyskinesia
- Bronchiectasis
- Cystic fibrosis
- Endotracheal tube
- Trauma
- Viral co-infection (viral infection can predipose and facilitate bacterial infection)
- Smoking (squamous cell metaplasia)
- HIV (or other immunocompromised conditions)
- Immune suppressive medications (including chemotherapy)
What are the 3 microbiological causes of pneumonia (microorganisms)
Bacteria, viruses and fungi
How are pneumonia-inducing bacteria characterized?
- Typical (eg. streptococcus pneumoniae) vs Atypical (eg. mycoplasma pneumoniae)
- Selected populations (very specific types of populations will be at risk for these organisms)
Why is understanding the microbiology of pneumonia important?
The microbiology determines the antibiotic of choice for treatment!
What demographic is most commonly affected by CAP?
Children and especially the elderly
What organisms are responsible for CAP in children, adults, and the elderly?
Children: respiratory viruses
Young adults: atypical bacteria
Elderly: S. pneumoniae
The organisms causing HAP will be different for people with … vs …
will be different for people with a normal immune system and immunocompromised individuals
What organisms are responsible for HAP in individuals with normal immune systems vs immune-compromised individuals?
Normal immune system: anaerobic infections
Immune-compromised: opportunistic bacteria, fungal infections, more drug-resistant organisms
Takeaway: What is the most common microbiological cause for CAP vs HAP?
CAP: viruses and atypical bacteria, streptococcus pneumoniae
HAP: Streptococcus pneumoniae is still common, but other organisms become problematic like S. aureus, gram-negative bacteria, anaerobes, opportunistic infections
What organism most commonly causes bacterial pneumonia? Describe some key facts (3) (CAP vs HAP, colonization, susceptible hosts)
Streptococcus pneumoniae
* 90% is CAP, but is still the most common cause of HAP
* can colonize the oropharynx without causing pneumonia
* susceptible hosts: young children, elderly, smokers, alcohol abuse, post-influenza
Strep. pneumoniae is
a) gram-positive
b) gram-negative
a) gram positive
Pathology of Strep. pneumoniae:
Inflammatory edema fills the alveolar airspace and spreads between the alveoli through…
the pores of Kohn
(airspace (lobar) pneumonia)
What are some clinical signs of Strep. pneumoniae
Acute onset, high fever, shaking, chills, pleuritic chest pain, rust coloured sputum (pretty typical of most pneumonia)
CXR: lobar pneumonia, air bronchograms
*Make sure you can recognize pneumonia on a CXR
What are some possible complications of Strep. pneumoniae?
Empyema, bacteremia
How does Strep. pneumoniae repsond to treatment?
Rapid response to treatment
What is the most common atypical organism that can cause pneumonia?
Mycoplasma pneumoniae
