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STREPTOCOCCUS PNEUMONIAE – microbio, morphology
- Gram (+)’ve in pairs and chains
- Often lancet shaped diplococci
- (Diplococcus pneumoniae)
- Nonmotile, no spores
- Important: Polysaccharide capsule which allows us to identify specific 90 types
- Qwellung reaction with type specific antiserum
- Has yielded to PCR
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Strep. pneumoniae
- Best in CO2 containing atmosphere
- Need catalas: blood or blood agar best; are ALPHA HEMOLYTIC (partial; green or viridans)
- Autolytic system: shortly after reaching plateau growth; may impede recovery from clinical specimens
- Optochin (quinidine derivitive) susceptible: Other viridans and streptococci are resistant
- Bile soluble – activates autolysin
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Streptococcus pneumoniae - Virulence factors
- Polysaccharide capsule
- External to cell wall
- Antiphagocytic
- Antigenically diverse – it is the anticapsular Abs that protect against disease
- Cell wall: fragments are pro-inflammatory
- Cell wall polysaccharide: antigenically conserved and is the same from strep to strep
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Pneumolysin
- Streptococcus pneumoniae-very important virulence factor
- Cell membrane protein equivalent to a toxin
- Blocking pneumolysin production attenuates virulence and prevents a lot of damage
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Colonization of pneumococcus in humans
- Asymptomatic in 5-15% of healthy adults and 20-65% of healthy children
- Spread requires prolonged and close contact
- Rates of colonization and infection are seasonal: winter
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Streptococcus pneumoniae- Pathogenesis
- Colonization of the nasopharynx: spread to sinuses or middle ear, microaspiration into lung
- Once in lung: proliferation in alveoli, spread to other alveoli impaired gas exchange
- Can move to lymphatics/ and/or get into blood stream, but NOT in all cases
- Seeding of remote body sites if bacteremic: meninges, peritoneum, bone, joints – INFREQUENT
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PNEUMOCOCCAL INFECTIONS
- Upper respiratory tract: sinusitis, acute or chronic / acute otitis media (“AOM”)
- Lung:
- Community-acquired pneumonia (CAP)
- Healthcare associated pneumonia (HCAP)
- May have associated empyema
- May result in bacteremia
- Remote infections following bacteremia: Meningitis, peritonitis, osteomyelitis, septic arthritis
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Predisposing conditions
- Immunodeficiency syndromes: HIV, IgG (& subclass) deficiency
- Splenic dysfunction/ splenectomy
- Cirrhosis, alcoholism
- Asthma, COPD
- Smoking
- Heart failure
- Malignancy: Myeloma, chronic lymphocytic leukemia (CLL), lymphoma
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Pneumococcus pneumoniae – clinical frequency
- Most common identified pathogen in adult Community-acquired pneumonia (CAP)
- 20-60% depending on methodology and definitions
- 30% of acute otitis media (“AOM”) with identified pathogens
- Commonest cause of bacterial meningitis in U.S. especially for ages
- 1-23 mos
- >60 yrs
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Pneumonia – clinical features
- Fever – release of cytokines: shaking chill
- Cough – inflammation in the lungs: “rusty” sputum – a little bit of blood that make it into the alveoli in the course of the infection
- Tachypnea – impaired gas exchange, cytokines:
- Pleuritic chest pain:
- May present atypically, esp in elderly: delirium, confusion
- IMPORTANT: HYPERBILIRUBINEMIA may occur! Not necessarily biliary tree infection, might be a lung infection!
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Diagnosis – pneumonia
- Sputum culture: must handle properly, negative in 50% of bacteremic cases
- Blood cultures:
- Urine pneumococcal antigen: Sensitivity 70-90% (higher if severe infection)/ Specificity 80-100% Useful even if Abx already started!
- Pleural fluid culture
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CXR in pneumonia
- “Lobar” – consolidative:
- May “lag” with acute presentation:
- May take weeks to completely clear:
- Do not repeat early unless evidence of progression, Rx failure, etc.
- Repeat 6-8 weeks after Rx in patients >40, especially if smokers – because may reappear and may be associated with an obstruction that don’t see right away
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Pneumococcal pneumonia – treatment
- Penicillin – has been the drug of choice and highly susceptible until mid-1980’s
- PCN resistance has steadily increased in U.S. and worldwide
- Resistance increasing also to other antibiotics
- Resistance mechanism – often from altered PCN binding proteins, sometimes due to transformation from other organisms
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Risk factors for penicillin resistant pneumonia
- Recent antibiotic use most important
- Very young (<1 year)
- Day care attendees
- Elderly
- Nursing home residents
- HIV infection
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Rx for pneumococcal pneumonia
- PCN susceptible strains:
- Penicillin
- Cephalosporins
- Fluoroquinolones
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PCN susceptible strains:
- Penicillin (high doses)
- Cephalosporins – often use first until know what it is.
- Fluoroquinolones– often use first until know what it is.
- Vancomycin
- Linezolid
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Pneumonia prediction tools
- PSI pneumonia Severity Index: Historical, physical, and lab data
- CURB65: confusion, urea, RR, BP, age>65
- Both discriminate between pts at high vs low risk of mortality, but are not absolutes, and good to use for deciding whether or not to hospitalize a patient
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Pneumococcal vaccines
- 2 vaccines available in the U.S.
- 23 valent polysaccharide (PPSV): safe, inexpensive, single dose, variable efficacy though, in the highest risk populations – the elderly (T-cell independent)
- 7 or 3 valent conjugated (PCV) – conjugated that makes the immunity T-cell dependent – reduces nasopharyngeal carriage of vaccine serotypes in children – decreases transmission as well, and to adults, and the elderly
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