Sputum samples are typically collected to diagnose tuberculosis.

• A. Diphtheria
• B. H. pylori
• C. Meningitis
• D. Tuberculosis

Answer: (D)

The key idea is that sputum is the appropriate diagnostic sample when the infection involves the lungs, because it carries the respiratory pathogens shed into the airways. In tuberculosis, Mycobacterium tuberculosis typically resides in the lungs and is expelled into the mucus during coughing. Analyzing sputum allows detection of the bacteria through methods like smear microscopy for acid-fast bacilli, culture to grow the organism, or molecular tests that identify TB DNA quickly. This direct link between where the disease is occurring and the sample collected is why sputum testing is standard for diagnosing active pulmonary TB. If a patient can produce sputum, this sample provides the most straightforward route to confirming TB.

Other conditions require different samples that reflect where the infection is most likely located. Diphtheria is diagnosed with a throat swab to detect the causative bacteria in the oropharyngeal region. H. pylori is typically diagnosed with a breath test, stool antigen test, or gastric biopsy, not sputum. Meningitis is diagnosed by examining cerebrospinal fluid obtained via lumbar puncture because the infection is in the meninges surrounding the brain and spinal cord.