Question
A 30-year-old female came to emergency department with productive cough, fever, chest pain and shortness of breath for past 4 days. On examination, her temperature was 1010F respiratory rate was 30/min, Chest examination revealed decreased breath sounds on left lung. Chest X-ray showed homogenous ground glass opacity in left lower lobe. Sputum upon gram staining showed gram positive cocci arranged in pairs with plenty of pus cells. (
- (a) What is the clinical condition. ( 1 mark(s)
- (b) What is the causative organism. ( 1 mark(s)
- (c) Enumerate the other causative organisms of this condition. ( 4 mark(s)
- (d) Laboratory diagnosis of the above condition. (e) Vaccine strategy for above condition. 5 mark(s)
Answer
(a) Clinical condition: Community-acquired lobar pneumonia.
(b) Causative organism: Streptococcus pneumoniae — Gram-positive cocci arranged in pairs (diplococci) with plenty of pus cells on sputum Gram stain is the classical finding.
(c) Other causative organisms of community-acquired pneumonia: Haemophilus influenzae, Mycoplasma pneumoniae, Klebsiella pneumoniae, Legionella pneumophila, and respiratory viruses (Influenza virus, RSV).
(d) Laboratory diagnosis:
- Sputum Gram stain and culture — Gram-positive diplococci (lancet-shaped) on Gram stain; culture on blood agar showing alpha-haemolytic, draughtsman-colonies, with optochin sensitivity and bile solubility distinguishing S. pneumoniae from other alpha-haemolytic streptococci (e.g., viridans group).
- Blood culture — positive in a proportion of cases, particularly useful given sputum contamination issues.
- Urinary pneumococcal antigen test — rapid, useful even after antibiotic initiation.
- Quellung reaction — capsular swelling test using type-specific antiserum, both for identification and serotyping.
- Chest X-ray — supportive, showing lobar consolidation/ground-glass opacity as in this patient.
(e) Vaccine strategy:
- Pneumococcal Conjugate Vaccine (PCV) — e.g., PCV13/PCV10, covering the most common invasive serotypes, recommended in infancy as part of the routine immunization schedule, inducing a T-dependent immune response with memory (effective even in young children, unlike plain polysaccharide vaccine).
- Pneumococcal Polysaccharide Vaccine (PPSV23) — covers 23 serotypes, recommended for high-risk adults (elderly, chronic disease, immunocompromised, asplenia) and children over 2 years in high-risk groups; T-independent response, less effective in children under 2 years.
- Vaccination strategy targets high-risk groups (infants, elderly, immunocompromised, chronic disease patients) to reduce the burden of invasive pneumococcal disease including pneumonia, meningitis, and bacteraemia.