MI7.1-5 | Respiratory Tract Infections — Practice Quiz

A 9-year-old boy presents with fever (38.8°C), tonsillar exudate, tender anterior cervical lymphadenopathy, and absence of cough. What is the most likely causative organism?

A throat swab Albert stain from a child with pseudomembranous pharyngitis reveals pleomorphic gram-positive rods with metachromatic granules arranged in a 'Chinese letter' pattern. Which toxin mechanism best explains the systemic complications?

In which clinical situation would Pneumocystis jirovecii (PCP) be the most important lower respiratory tract pathogen to consider?

A 35-year-old teacher presents with low-grade fever, dry cough, headache, and mild chest X-ray infiltrates disproportionate to his relatively well appearance. He does not respond to amoxicillin. Which organism is the most likely cause, and why does it not respond to beta-lactams?

Ziehl-Neelsen staining of a sputum sample shows slender, beaded, acid-fast bacilli. The culture grows slowly over 6 weeks on Löwenstein–Jensen medium, producing buff-coloured, rough colonies. Which property of the organism's cell wall is responsible for acid-fastness?

Which of the following best describes the sputum quality criteria that must be met before processing a sputum sample for lower respiratory tract infection diagnosis?

A 50-year-old diabetic man presents with severe pneumonia. His sputum Gram stain shows large Gram-negative rods encapsulated in a thick mucoid capsule. The sputum is described as 'currant jelly' (blood-stained mucoid). Which organism should be suspected?

During an NTEP clinic, a patient with suspected pulmonary tuberculosis has sputum collected for CBNAAT (Xpert MTB/RIF). The test detects Mycobacterium tuberculosis with RIF resistance. Which mutation is most commonly responsible for rifampicin resistance?

A 5-year-old child presents with a 3-day history of barking cough, inspiratory stridor, and low-grade fever. A frontal chest X-ray shows subglottic narrowing ('steeple sign'). Which is the most common causative pathogen?

In a hospital microbiology laboratory, a throat swab sample is directly inoculated onto Blood Agar, MacConkey Agar, and Tellurite agar. The Tellurite agar shows grey-black colonies with a brown halo. What is the most likely identification?