Which of the following statements about tuberculosis are correct? a) Ziehl‑Neelsen stain is used for diagnosis in sputum, b) Cavitary tuberculosis shows diffuse lung damage on chest X‑ray, c) In primary tuberculosis the primary focus is usually not visible on chest X‑ray, d) Antituberculosis therapy consists of an initial bactericidal phase of two months followed by a sterilizing phase of four months, e) A tuberculin skin test (Mantoux) induration > 5 mm is considered positive in individuals without risk factors.

Tuberculosis: Statement Analysis

Statements (a), (c), and (d) are correct; statement (b) is incorrect as cavitary TB shows focal cavitation rather than diffuse damage; statement (e) is incorrect because >5 mm Mantoux positivity applies only to high-risk individuals, not those without risk factors.

Statement-by-Statement Analysis

Statement (a): Ziehl-Neelsen Stain for Sputum Diagnosis - CORRECT

• Ziehl-Neelsen staining is the standard acid-fast bacilli (AFB) stain used to identify Mycobacterium tuberculosis in sputum specimens. 1
• A positive AFB smear provides strong evidence for the diagnosis of tuberculosis and is used to assess infectiousness. 1
• The most infectious persons are those with positive AFB sputum smears, particularly when combined with cavitation on chest radiograph. 1

Statement (b): Cavitary TB Shows Diffuse Damage on Chest X-ray - INCORRECT

• Cavitary tuberculosis demonstrates focal cavitation in the lungs, not diffuse damage. 1
• Chest radiographs in cavitary TB typically show upper lobe fibro-cavitary disease with discrete cavities, not diffuse infiltrates. 2
• Cavitation on chest radiograph is a specific indicator of high infectiousness and correlates with higher bacterial burden. 1
• Diffuse infiltrates are more characteristic of atypical presentations, particularly in immunocompromised patients, not classic cavitary disease. 2

Statement (c): Primary TB Focus Usually Not Visible on Chest X-ray - CORRECT

• In primary tuberculosis, particularly in children, the primary focus (Ghon complex) is often not visible on standard chest radiography. 1
• Children with typical primary tuberculous lesions frequently do not show obvious radiographic abnormalities unless they have extensive pulmonary involvement or cavitation. 1
• CT chest is superior to plain radiography for detecting subtle primary TB lesions, especially in immunocompromised patients where chest X-rays are frequently deceptively normal. 2

Statement (d): Two-Phase Treatment (2 Months Initial, 4 Months Continuation) - CORRECT

• The standard tuberculosis treatment regimen consists of a 2-month intensive (bactericidal) phase followed by a 4-month continuation (sterilizing) phase. 1, 3
• The initial phase uses isoniazid, rifampin, pyrazinamide, and ethambutol daily for 2 months (56 doses over 8 weeks). 1, 3, 4
• The continuation phase uses isoniazid and rifampin daily for 4 months for most patients. 1, 3
• A 7-month continuation phase is required only for specific high-risk groups: patients with cavitary pulmonary TB who remain culture-positive at 2 months, those whose initial phase did not include pyrazinamide, or those receiving once-weekly isoniazid-rifapentine who were culture-positive at 2 months. 1

Statement (e): Mantoux >5 mm Positive in Individuals Without Risk Factors - INCORRECT

• A Mantoux test >5 mm is considered positive only in high-risk individuals, not in those without risk factors. 1
• Three distinct cut-points exist for defining positive tuberculin reactions based on risk stratification: 1
  • ≥5 mm: HIV infection, immunosuppressive therapy, recent close TB contact, or abnormal chest radiographs consistent with prior TB 1, 2
  • ≥10 mm: Recent immigrants from high-prevalence countries, injection drug users, residents/employees of high-risk congregate settings, healthcare workers with TB exposure, mycobacteriology laboratory personnel, and persons with clinical conditions increasing TB risk (silicosis, diabetes, chronic renal failure, malignancies, significant weight loss) 1
  • ≥15 mm: Persons at low risk for TB, for whom tuberculin testing is not generally indicated 1

Critical Clinical Pitfalls

• Never rely on chest radiography alone in immunocompromised patients—proceed directly to CT chest as plain films are frequently normal despite active disease. 2
• Never discontinue pyrazinamide for asymptomatic hyperuricemia alone, as this is expected and clinically insignificant. 3
• Never add a single drug to a failing TB regimen, as this promotes drug resistance. 3
• Negative tuberculin skin tests do not exclude active TB in immunocompromised patients due to anergy. 1, 2
• The terminology has evolved: the "bactericidal phase" and "sterilizing phase" both contribute to bacterial killing, but the initial intensive phase rapidly reduces bacterial burden while the continuation phase eliminates persistent organisms. 1, 3