Streptococcus pneumoniae
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Background:
Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, lancet-shaped diplococcus, often appearing in pairs. It is encapsulated, which significantly enhances its virulence. It exhibits alpha-haemolysis on blood agar and is optochin-sensitive, distinguishing it from other streptococci. It is a facultative anaerobe and is commonly part of the normal nasopharyngeal flora, particularly in children.Spectrum of clinical illness:
Streptococcus pneumoniae is responsible for a wide range of non-invasive and invasive infections, including:Respiratory infections:
- Community-acquired pneumonia (CAP) – often presenting with lobar consolidation
- Acute otitis media
- Acute sinusitis
- Acute exacerbations of chronic bronchitis
- Bacteraemia
- Meningitis: particularly in young children, older adults, and immunocompromised individuals
- Septicaemia: especially in asplenic patients
- Septic arthritis
- Osteomyelitis
- Endocarditis (less common)
Transmission:
Transmission occurs via respiratory droplets from carriers or symptomatic individuals. The bacteria frequently colonise the nasopharynx, particularly in children, who act as reservoirs. Spread is more common in crowded or institutional environments, such as nurseries, care homes, and hospitals.
Treatment:
- Penicillin or amoxicillin (often used first line)
- Ceftriaxone or cefotaxime (in cases of resistance or severe infection)
- Vancomycin for highly resistant strains or in meningitis
- Macrolides e.g. clarithromycin or fluoroquinolones (e.g. levofloxacin) in penicillin-allergic patients
Vaccination:
The pneumococcal conjugate vaccine (PCV) is included in the UK’s childhood immunisation programme. 1 dose is given at 12 weeks of age with a booster dose at 12–13 months of age
The pneumococcal polysaccharide vaccine (PPV23) is also offered to adults aged 65 and over, and to high-risk groups such as those with splenectomy, chronic illnesses, or immunosuppression.