CDC Guidelines for Tuberculosis Diagnosis, Risk Assessment, and Infectiousness

Latent Tuberculosis Infection (LTBI)

Positive tuberculin skin test (TST) or interferon‑γ release assay (IGRA) indicates immune recognition of Mycobacterium tuberculosis antigens in screened individuals (CDC) 1
Targeted TST/IGRA testing is advised only for high‑risk populations—close contacts of active TB cases, foreign‑born persons from high‑prevalence countries, residents or workers in congregate settings, healthcare workers serving high‑risk groups, medically underserved groups, and children exposed to high‑risk adults—because these groups would benefit from treatment if positive (CDC) 2
Major risk factors that markedly increase progression from LTBI to active disease include HIV infection, recent infection (< 2 years), immunosuppressive therapy (TNF‑α antagonists, ≥15 mg prednisone daily, post‑transplant medications), age < 5 years, prior inadequately treated TB with fibrotic lesions, silicosis, and diabetes mellitus (CDC) 2

The recommended microbiologic algorithm is to obtain three sputum specimens on separate days for acid‑fast bacilli (AFB) smear microscopy and mycobacterial culture (CDC) 3
In the United States, ≈ 60 % of patients with culture‑confirmed TB have a positive AFB smear; thus a negative smear does not exclude disease (CDC) 4
HIV‑infected patients have lower rates of positive AFB smears because they less frequently develop cavitary disease (CDC) 4

Chest radiographs suggestive of active pulmonary TB include upper‑lobe infiltrates with cavitation or patchy/nodular infiltrates in apical or sub‑apical posterior upper lobes or superior segment of the lower lobe (CDC) 4
HIV‑infected patients may present atypically with infiltrates in any lung zone, mediastinal/hilar adenopathy, or even a normal chest radiograph (CDC) 4

Patients are considered infectious when they have pulmonary or laryngeal TB with cough, a positive AFB sputum smear, or cavitation on chest radiograph, especially if they are not responding adequately to chemotherapy (CDC) 5
Factors that increase infectiousness include disease located in the lungs, airways, or larynx; presence of cough or forceful expiratory maneuvers; failure to cover mouth/nose when coughing; inadequate or short‑duration chemotherapy; and aerosol‑generating (cough‑inducing) procedures (CDC) 5
Extrapulmonary TB is generally not infectious unless accompanied by concurrent pulmonary disease, involvement of the respiratory tract/oral cavity, or an open, heavily draining lesion (CDC) 5
Children are less likely than adults to be infectious, but transmission can occur; assessment follows the same criteria used for adults (pulmonary/laryngeal disease, cough, positive smear, cavitation) (CDC) 5
HIV coinfection does not appear to affect the infectiousness of TB patients, although HIV‑infected individuals have a higher risk of extrapulmonary disease and may show atypical radiographic findings (CDC) 5

Patients with LTBI are completely asymptomatic with no signs or symptoms of TB disease, and have a positive tuberculin skin test (TST) or interferon-gamma release assay (IGRA), with normal chest radiography and negative bacteriologic studies 6, 7, 8, 9
The lifetime reactivation risk of LTBI is 5-15%, with the majority occurring within the first 5 years after initial infection, according to the European Respiratory Society 6
Individuals with LTBI are not infectious to others 6

The American Thoracic Society recommends that patients with active TB disease be evaluated for clinical, bacteriological, and/or radiographic evidence of current tuberculosis disease 7, 10
Primary tuberculosis is characterized by a lobar pneumonia pattern on chest radiography, mediastinal and hilar lymphadenopathy, and is most commonly seen in children and severely immunocompromised individuals, as reported by the Journal of the American College of Radiology 11
Reactivation tuberculosis is characterized by apical posterior upper lobe or superior-segment lower lobe fibrocavitary disease, and endobronchial spread through airways with tree-in-bud nodules on CT, according to the Journal of the American College of Radiology 11
Common clinical signs and symptoms of active TB disease include cough lasting ≥2-3 weeks, fever, night sweats, weight loss, and hemoptysis, as summarized by Praxis Medical Insights 10, 12, 9
The gold standard for diagnosis of active TB disease is positive mycobacterial culture, and patients are infectious and require isolation until three consecutive negative sputum smears on different days, as recommended by Praxis Medical Insights 10, 9

The American College of Radiology recommends that chest radiography be used to show infiltrates, cavitations, or lymphadenopathy in patients with active TB disease 11, 10
The Centers for Disease Control and Prevention advise against excluding TB based on negative AFB smears alone, and against assuming non-infectiousness immediately after starting treatment, as reported by Praxis Medical Insights 9, 10
The World Health Organization recommends maintaining a high suspicion of TB in HIV-infected patients who may have atypical presentations or false-negative skin tests, as summarized by Praxis Medical Insights 12, 9