When evaluating suspected community-acquired pneumonia (CAP), which combination of investigations provides the highest diagnostic yield for both typical and atypical pathogens?
- A Sputum Gram stain with culture, urinary pneumococcal and Legionella antigen tests, and respiratory NAAT panel ✓
- B Blood culture and sputum AFB smear
- C Cold agglutinin titre and complement fixation test for Mycoplasma only
- D Serology for all atypical pathogens in the acute phase sample
Explanation
A comprehensive CAP microbiological work-up includes sputum Gram stain/culture (for typical bacteria), urinary Legionella antigen (sensitivity 80–95% for L. pneumophila serogroup 1), urinary pneumococcal antigen (sensitivity 70–80% for invasive disease), and a respiratory multiplex NAAT panel (detects atypical organisms including Mycoplasma, Chlamydophila, Legionella, and viruses). Cold agglutinins are non-specific for Mycoplasma. Acute-phase serology for atypical pathogens is not useful as a ≥4-fold titre rise between acute and convalescent samples is needed for confirmation, making it only a retrospective tool.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.