Community Acquired Pneumonia

Question 0

Other than optochin, what is s. pneumonia sensitive to?

Answer 0

Bile lysis

Question 1

What are the different routes of infection of CAP?

Answer 1

Microaspiration - s. pneumonia, h. Flu
Massive aspiration - normal flora anaerobes
Inhalation
Hematogenous spread - s. aureus, s. typhi, others

Question 2

What is the prevalence of s. pneumonia as a cause of CAP?

Answer 2

*20-60%

Question 3

What are common clinical presentations of s. pneumonia?

Answer 3

Respiratory tract - upper airway (sinusitis, otitis), lower airway (bronchitis, pneumonia, empyema, bacteremia)
Endocarditis
Meningitis
Arthritis 
Spontaneous bacterial peritonitis

Question 4

What are the risk factors for s. pneumonia?

Answer 4

Younger than 2 or older than 65
A splenic or hyposplenia
Alcoholism
Diabetes 
HIV infection
Antecedent flu
Recent acquisition of new virulent strain
Defects in humoral immunity

Question 5

What are the virulence factors of s. pneumonia?

Answer 5

Capsule - Smooth = encapsulated = virulent
Spontaneous phase variation occurs
High negative charge inhibits complement and Fc interxn with receptor
Pneumolysin - forms pores in host cells
Surface protein A - anti antibodies are protective
Surface antigen A
IgA protease

Question 6

How does s. pneumonia evade mechanical barriers for aspiration below the larynx?

Answer 6

Increased with decreased levels of consciousness
Increased with opiates, alcohol, barbiturates, benzodiazepines
Increased with neurological disease - absence of gag reflex

Question 7

When does s. pneumonia evade mechanical barriers through lack of mucociliary clearance?

Answer 7

Happens in smoking, COPD, bronchiectasis

Question 8

What are host defenses against s. pneumonia?

Answer 8

Colonization - mucosal IgA against capsule
Lungs - alveolar macrophages, PMN recruitment, TH1 cytokines
Blood - igG2, C3, c reactive protein, splenic clearance

Question 9

What is the pathogenesis of s. pneumonia?

Answer 9

Aspiration from nasopharynx
Failure of clearance mechanism
Intra alveolar spread through pores of Kohn and small airways
Congestion
Red hepatization - PMNs, RBCs, fibrin in alveoli
Gray hepatization - degeneration of cellular infiltrate and reabsorption
Resolution

Question 10

What is the clinical presentation of s. pneumonia?

Answer 10

Abrupt onset with shaking fever, chill
Productive cough with *rust colored sputum
Pleuritic chest pain
Referred abdominal pain if lower lobe disease
Atypical presentations in elderly or immunosuppressed

Question 11

What does the physical exam of a patient with s. pneumonia reveal?

Answer 11

Fever
Splinting of affected side
Tactile fremitus
Auscultation - inspiratory crackles, e->a changes, whispered pectoriloquy
Pleural effusion - dullness to percussion, decreased breath sounds
Hypoxemia due to v/q mismatch

Question 12

How is diagnosis of s. pneumonia made?

Answer 12

Cultures from blood or pleural fluid definitive but often negative
Sputum culture not sensitive or specific
Sputum gram stain - *adequate specimen >25 PMNs, <10 SECs
*antigen test - urine for diagnosing pneumonia and CSF for diagnosing meningitis

Question 13

What is penicillin resistant s. pneumonia (PRSP)?

Answer 13

Mutations of penicillin binding proteins
Risk factors are recent antibiotic therapy or hospitalization, children in day care
*highly resistant (MIC>2ug/ml) strains often resistant to other antibiotics

Question 14

What is macrolide resistance with s. pneumonia?

Answer 14

Common in PRSP
Resistance to erythromycin, azithromycin, clarithromycin
Erm (B) gene - ribosomal methylation, MIC >64 high level resistance
Mef (E) gene - efflux pump mechanism, MIC <32 low level resistance

Question 15

What is the natural history of s. pneumonia with treatment?

Answer 15

Fever and tachycardia resolve in 48 hrs

CXR normal after 3 weeks in healthy, may take up to 4 months in chronically ill patients

Question 16

What is the pneumococcal vaccine protective against?

Answer 16

Prevents bacteremia, not pneumonia

Question 17

What are the clinical features of aspiration pneumonia?

Answer 17

History of reason for impaired consciousness
Insidious onset
Low grade fever, purulent, *foul smelling sputum, weight loss
Poor dental hygiene, cachexia
Often upper lobes, often cavities
Sputum stain and culture has mixed oral flora with PMNs

Question 18

What is the treatment for aspiration pneumonia?

Answer 18

*clindamycin or penicillin derivative for several months

Question 19

How does droplet size affect inhalation of infected droplets causing CAP?

Answer 19

> 10 micrometers - likely to land in upper respiratory tract
1-5 micrometers - deposits in bronchi, alveoli
<1 micrometer - remains airborne

Question 20

What are the main differences between typical pneumonia and atypical pneumonia?

Answer 20

• typical - abrupt onset, rapid progression, and often lobar distribution
• atypical - gradual onset, slow progression, patchy distribution

Question 21

What are common causes of atypical pneumonia?

Answer 21

Mycoplasma pneumoniae
Clamydophila pneumoniae
Legionella pneumophila

Question 22

How does mycoplasma pneumoniae culture?

Answer 22

Difficult 
Slow growth on cell free media
Both aerobic and anaerobic
Mulberry or fried egg colonies
No cell wall

Question 23

How does mycoplasma pneumoniae cause infection?

Answer 23

Adheres to respiratory epithelial cells, inhibits ciliary action, induces sloughing of ciliated cells
Attachment via terminal organelle on bacteria and glycoproteins on epithelial cell
Produces hydrogen peroxide which causes damage

Question 24

What are the clinical features of mycoplasma pneumoniae?

Answer 24

*ambulatory young persons 
Fever, malaise, headache, cough 
*walking pneumonia - chest clear despite abnormal CXR
Unusual severity: sickle cell
Extra pulmonary manifestations

Question 25

What are extra pulmonary manifestations of mycoplasma pneumoniae?

Answer 25

Cold agglutins - IgM antibodies to I antigen on RBCs, reversible
Might cause hemolysis and raynauds
Can cause distal necrosis in patients with sickle cell due to microvascular occlusions
Most commonly neurologic complications

Question 26

How is mycoplasma pneumoniae diagnosed?

Answer 26

Culture difficult and not attempted
PCR on throat swab - accurate but not readily available
Direct antigen testing
Cold agglutins titer - > 1:32 is suggestive
Serology - anti mycoplasma IgM and IgG

Question 27

What are the basics of clamydophila and CAP?

Answer 27

Obligate intracellular parasite
Elementary bodies are infectious 
Asymptomatic infection is common
Illness often mild and slow progression 
Diagnosed with microimmunofluorescence antibody test

Question 28

What diseases are caused by legionella pneumophila?

Answer 28

Legionnaire’s disease - pneumonia, often fatal

Pontiac fever - influenza like illness, rarely fatal

Question 29

Where does legionella live and how is it spread?

Answer 29

Lives in fresh water - no human reservoir

Spread via aerosols, not person to person (outbreaks associated with moving water machines)

Question 30

What is legionnaires disease?

Answer 30

Incubation 2-10 days
Myalgia, headache, fever, cough
Diarrhea
Bilateral infiltrates

Question 31

What is Pontiac fever?

Answer 31

Incubation 20-48 hrs
Fever, myalgia, dry cough
No treatment needed

Question 32

What is the pathogenesis of legionella?

Answer 32

Inhalation in droplets reach alveoli and bronchioles
Infection of alveolar macrophages and multiplication inside ER derived sac
Destroy cell and spread

Question 33

How does immunity to legionella work?

Answer 33

Cell mediated, not really antibodies

Interferon gamma activates macrophages so they can kill it

Question 34

How is legionella diagnosed?

Answer 34

*urine antigen test - for serotype 1 only
Not gram stain
Culture on special media
Serology
Direct FA of sputum, PCR of sputum or bronchoalveolar lavage fluid

Question 35

How is legionella treated?

Answer 35

Macrolides like azithromycin
Fluroquinolones
Rifampin with something else
Beta lactams and aminoglycosides don’t work - need something that concentrates in phagolysosome

Question 36

Which causes of CAP are common in AIDs patients depending on cd4 count?

Answer 36

CD4 < 400 - m. TB, s. pneumonia (h. Flu, s. aureus)
CD4 < 200 - pneumocystis jiroveci
CD4 < 50-100 - pseudomonas, disseminated m. TB, non-tb myco, cryptococcus neoformans, CMV