An 8-year-old boy presents with 10 days of low-grade fever, dry hacking cough, and malaise. Examination reveals scattered crackles but no wheeze. Chest X-ray shows bilateral perihilar interstitial infiltrates out of proportion to his mild findings. Total leukocyte count is normal. Cold agglutinins are positive. The most likely causative organism is:

• A Mycoplasma pneumoniae ✓
• B Haemophilus influenzae type b
• C Streptococcus pneumoniae
• D Staphylococcus aureus

Explanation

Mycoplasma pneumoniae is the leading cause of atypical or walking pneumonia in school-aged children, characterised by insidious onset, prominent cough, sparse physical signs, interstitial radiographic changes, normal leukocyte count, and positivity for cold agglutinins. S. pneumoniae causes abrupt lobar consolidation with high fever and leukocytosis, while H. influenzae and S. aureus present as acute bacterial illness rather than a subacute course over days to weeks.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.