PNA clinical and microbiological aspects

Question 1

Pneumonia

Answer 1

• Infection of the pulmonary parenchyma by one or more of the following pathogens: bacterial, viral, fungal, parasitic
• Hx: cough, fever, chills, pleuritic chest pain, headache, myalgia
• Specific to organisms: splenectomy (S pneumo), Hx of travel (systemic mycoses)
• PE: abnormal breath sounds/signs of lung consolidation/effusion
• Infiltration on CXR
• Sputum gram stain useful only if not contaminated

Question 2

Strep pneumo PNA

Answer 2

• Most common CAP w/ identifiable cause
• The GP lancet shaped diplococci (alpha hemolytic, catalase negative) cause a lobar (consolidation) PNA
• They are capsulated (splenectomy is risk factor)
• Increasing B-lactam and macrolide resistance
• Vaccine (conjugated) for children and elderly

Question 3

Haemophilus influenzae

Answer 3

• GN coccobacillus that commonly colonizes nasopharynx
• Does not cause the flu (flu is influenza virus)
• Commonly causes otitis media, sinusitis, PNA especially in COPD and elderly
• Most strains resistant to B-lactams, erythromycin

Question 4

Moraxella catarrhalis

Answer 4

• GN coccobacillus, commonly carried in URT
• Causes otitis media, sinusitis
• PNA in elderly and those w/ underlying disease

Question 5

Klebsiella pneumoniae

Answer 5

• GN bacillus (enterobacterium) that has capsule
• Pts at risk: alcoholics, COPD pts
• Can cause hospital acquired PNA
• Finiding: necrotizing PNA, currant jelly sputum, buldging fissure sign

Question 6

Staph Aureus

Answer 6

• GP coccus, catalase positive, coagulase positive
• Uncommon cause of community acquired PNA, but most common cause of hospital acquired PNA
• Lung necrosis and abscess formation
• MRSA increasing in incidence

Question 7

Typical vs atypical PNA

Answer 7

• Typical: fevers, chills, pleuritic pain, productive cough, lobar pattern on CXR
• Atypical: fever, headache, myalgias, non-productive cough (worse at night), bronchoPNA/interstitial pattern on CXR

Question 8

Mycoplasma pneumoniae

Answer 8

• Classic cause of atypical PNA
• Frequent cause of PNA in adults and especially children
• Usually mild and self-limiting but can be severe (esp in elderly)
• Dx via PCR
• Can cause bullous myringitis: tympanic membrane erythema (inflammation) and whiskers

Question 9

Chalmydophila pneumoniae

Answer 9

• Very common cause of CAP, many cases are mild or sub-clinical
• Dx can only be made by acute and convalescent titers in sera

Question 10

Legionella sp

Answer 10

• GN rod, intracellular parasite
• Water is a major source, no person-person transmission
• Syndromes: pontiac fever (mild nonPNA illness), legionnaires disease (PNA w/ non-specific presentation, hyponatremia common as is lobar pattern)
• Dx: urinary Ag and PCR
• Host factors (COPD, immunosuppression, smoking) influence outcome

Question 11

Q fever

Answer 11

• Caused by Coxiella burnetti, caught via spore form inhalation
• Acute: PNA
• Chronic: endocarditis, hepatitis
• Associated w/ farming

Question 12

Chalmydia psittaci

Answer 12

• Transmitted from pet birds to humans
• Illness ranges from ASx to severe PNA
• Fever, chills, nonproductive cough, pulse-temp dissociation

Question 13

Transmission of PNA

Answer 13

• Usually form aspiration of organisms in the oropharynx

- Or by inhalation of infected aerosol particles (must be <5um to reach LRT)

Question 14

Rx of PNA

Answer 14

• Must be started immediately, Rx chosen based on the organism its likely to be
• Previously healthy, no risk factors for drug resistance strep pneumo: macrolide or doxycycline
• COPD/underlying disease/risk factor for DRSP/in pt Rx: fluoroquinolone (levofloxacin) for 5-7 days or B-lactam plus macrolide