Streptococcus pneumoniae

From IDWiki
Streptococcus pneumoniae

Background

Microbiology

  • Gram-positive, lancet-shaped diplococcus
  • 90+ serotypes, based on capsular polysaccharide that is bound to peptidoglycan
  • Lab identification is based on catalase negative, α hemolysis of blood agar (from pneumolysin), optochin susceptibility, and bile salt solubility
  • Via transformation, bacteria can exchange genetic material with each other

Antibiotic Resistance

  • Penicillin resistance
    • S. pneumoniae has 6 PBPs: 1A, 1B, 2A, 2B, 2X, and 3
    • Resistance in any of the PBPs can increase the MIC
    • Mutations in PBP 2B are associated with low-level resistance
    • Mutations in PBP 2X are associated with high-level resistance
  • Macrolide resistance
    • ermB encodes an enzyme that methylates the 23S subunit, blocking macrolides and giving very high MIC ≥64
    • mefA encodes an efflux pump that gives a relatively lower MIC ≤16

Epidemiology

  • Present worldwide
  • Major cause of morbidity and mortality in children
    • Leading cause of under-5 mortality worldwide

Pathophysiology

  • Acquired by coughing and sneezing
  • Asymptomatic carriage or colonization in the nasopharynx
  • Invasion through epithelial cells into the bloodstream, using the PAF and pIg receptors
  • Capsule and various proteins help it to evade immune system

Clinical Manifestations

Asymptomatic Carriage

  • 4-10% in the general adult population, usually lasting several weeks
  • Highest in children, up to 30-60% depending on the situation, lasting up to 6 months

Otitis Media

Sinusitis

Bacteremia

Pneumonia

  • Acute onset of cough (92%), fatigue (63%), shortness of breath (47%), and dyspnea (23%) with documented or subjective fever (92%), chills (77%), sweats, purulent sputum, and pleuritic chest pain (79%)

Meningitis

  • Most common cause of bacterial meningitis in adults
  • Acquired by hematogenous spread from nasopharynx, or direct invasion from sinuses
  • May be secondary to otitis media or sinusitis
  • CSF leaks and other defects predispose to infection
  • Diagnostic yield in CSF decrease significantly 4 hours after administration of antibiotics

Management

Scenario Penicillin (μg/mL) Ceftriaxone (μg/mL)
S I R S I R
Non-meningitic oral ≤0.06 0.12-1 ≥2
Non-meningitic parenteral ≤2 4 ≥8 ≤1 2 ≥4
Meningitic ≤0.06 ≥0.12 ≤0.5 1 ≥2

Prevention

Vaccination

  • Essentially two forms of vaccine available in Canada
    • Pneu-C-13: 13-valent pneumococcal conjugate vaccine (Prevnar-13)
      • More immunogenic, but fewer serotypes
      • Routine childhood immunization, also used for immunocompromised adults
      • Includes serotypes: 4, 9V, 6B, 14, 18C, 19F, 23F, 1, 5, 7F, 3, 6A, and 19A
      • Given at least 1 year after Pneu-P-23
    • Pneu-P-23: 23-valent pneumococcal polysaccharide vaccine (Pneumovax)
      • Less immunogenic, but more serotypes
      • Routine immunization in elderly
      • Includes above serotypes (except 6A), plus 2, 8, 9N, 10A, 11A, 12F, 15B, 17F, 20, 22F, and 33F
      • Given at least 8 weeks after Pneu-C-13 and at least 5 years after most recent Pneu-P-23 (except HSCT patients)
      • Booster given at 5 years if they are at risk of poor antibody response
Age Status Vaccine
<18 routine 2 to 4 doses PC-13, depending on age
18-64 healthy no routine vaccination
smoking, alcohol, injection drug use, homeless, long-term care facility 1 dose PP-23
high risk for invasive disease 1 dose PP-23 ± booster at 5 years
≥18 immunocompromised 1 dose PC-13, followed in 8 weeks by 1 dose PP-23 with booster at 5 years
HSCT recipient 3 doses PC-13 q4wk starting 3-9 months post-transplant, followed 6-12 months later by 1 dose PP-23 ± booster at 1 year
≥65 healthy, regardless of prior vaccination 1 dose PP-23

Post-Exposure Management

  • Per Public Health Ontario, no specific management is required for close contacts