Streptococcus pneumoniae - S. pneumoniae

Streptococcus pneumoniae - S. pneumoniae

 

Streptococcus pneumoniae causes pneumococcal disease.

Epidemiology

  • Incidence – kills more people in the U.S. (40,000) than any other vaccine-preventable disease
  • Transmission – humans are the natural reservoir for S. pneumoniae; organism colonizes in nasopharynx

Organism

  • S. pneumoniae are typically gram-positive, lancet-shaped diplococci
  • S. pneumoniae that are pathogenic in humans are heavily encapsulated
    • Virulence determined by composition of capsular polysaccharide
    • Antibodies to capsular polysaccharides confer type-specific immunity

Clinical Presentation

  • Pneumonia
    • S. pneumoniae responsible for 50% of all cases of community-acquired pneumonia
      • Often develops during upper respiratory tract viral infections with influenza and measles
      • Bacteremia occurs in 25-40% of patients
        • S. pneumoniae causes 85% of all cases of bacteremia in pediatric population
        • Overall mortality rate for bacteremia is 20% but may reach 60% in elderly patients
  • Otitis media
    • Responsible for 30–50% of otitis media cases
      • About 90% of children in U.S. have at least 1 episode by age 3
      • 50% have >6 episodes
  • Sinusitis
    • Responsible for 40% of sinusitis cases 
  • Meningitis

Diagnosis

  • Laboratory testing
    • Antigen-based testing
      • Meningitis (CSF and urine specimens)
      • Bacteremia and pneumonia (urine specimens)
      • Caution: Children may asymptomatically shed S. pneumoniae antigen in urine decreasing clinical specificity of assay.
    • Gold standard – culture (blood and CSF)

Treatment

  • Effectively treated with antibiotics unless:
    • Treatment is delayed
    • Bacteria are resistant
    • Patient has another debilitating illness or is immunocompromised
  • Current vaccines recommended by the CDC
    • Adults – 23-valent polysaccharide vaccine (PPV23, Pneumovax™)
    • Pneumovax™ – serotypes included in the vaccine are 1, 2, 3, 4,  5,  6B, 7F, 8,  9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F, 33F
    • Infants and toddlers – 7-valent polysaccharide conjugate vaccine (PCV7, Prevnar™)
    • Prevnar™ – serotypes included in the vaccine are 4,6B, 9V, 14,18C, 19F, 23F
    • Currently, clinical trials in progress for 9 and 11 valent-conjugated vaccines that will add serotypes 1 and 5, followed by serotypes 3 and 7F

See Also