When are you contagious with tuberculosis?

When You Are Contagious with Tuberculosis

You are contagious with tuberculosis when you have active pulmonary or laryngeal disease that is untreated or inadequately treated, particularly if you are coughing, have positive acid-fast bacilli (AFB) sputum smears, or have cavitary disease on chest radiograph. 1

Who Is Contagious

Most Infectious Patients

The highest risk for transmission comes from individuals who have: 1

• Pulmonary or laryngeal TB with cough or undergoing cough-inducing procedures
• Positive AFB sputum smears indicating high bacterial loads
• Cavitation on chest radiograph showing extensive lung destruction
• No treatment or inadequate treatment allowing continued bacterial multiplication

Non-Contagious TB Forms

You are NOT contagious if you have: 1, 2

• Latent TB infection (LTBI) - asymptomatic with negative chest radiographs and cannot transmit infection to others
• Extrapulmonary TB only (unless you also have concomitant pulmonary disease, disease in the respiratory tract/oral cavity, or an open abscess with extensive drainage) 1

When Contagiousness Decreases with Treatment

Rapid Initial Decline

After starting standard multidrug therapy (isoniazid, rifampin, pyrazinamide, ethambutol), your infectiousness drops dramatically within the first 2 days, primarily due to isoniazid killing viable bacteria. 1

The bacterial load in sputum decreases: 1

• >90% (10-fold) within 2 days of starting treatment
• >99% (100-fold) by days 14-21 due to rifampin and pyrazinamide effects

Criteria for Non-Infectiousness in Outpatient Settings

For patients with drug-susceptible TB being discharged home, you can be considered non-infectious after 2-3 weeks of standard multidrug therapy if ALL of the following are met: 1

• Negligible likelihood of multidrug-resistant TB
• Received standard multidrug anti-TB therapy for 2-3 weeks (or 5-7 days if sputum AFB smears were negative or rarely positive)
• Complete adherence to treatment (ideally directly observed therapy)
• Clinical improvement (reduced cough frequency, decreased sputum AFB smear grade)
• All close contacts identified, evaluated, and started on treatment if indicated

Stricter Criteria for Hospitalized or Congregate Settings

While hospitalized or in congregate settings (shelters, correctional facilities, nursing homes), you must remain in airborne isolation until: 1, 3

• Receiving standard multidrug anti-TB therapy
• Demonstrated clinical improvement
• Three consecutive negative AFB sputum smears collected 8-24 hours apart on different days, with at least one early-morning specimen

This stricter standard exists because close contacts cannot be identified and protected in these settings. 1

Special Populations

Children

Children with typical primary TB lesions are usually NOT contagious because they: 1, 4

• Rarely produce forceful coughs needed to aerosolize bacteria
• Rarely develop cavitary lesions with high bacterial loads
• Often have negative sputum AFB smears

However, children CAN be infectious if they have: 1, 4

• Laryngeal or extensive pulmonary involvement
• Pronounced cough or undergoing cough-inducing procedures
• Positive sputum AFB smears
• Cavitary TB on chest radiograph
• No therapy, just started therapy, or inadequate therapy

Drug-Resistant TB

If you have suspected or confirmed multidrug-resistant TB, you remain contagious much longer—potentially weeks to months—and require the stricter criteria of three consecutive negative sputum smears before being considered non-infectious. 1, 3

Critical Pitfalls to Avoid

Do not assume a single negative test (like BAL AFB PCR) means you are non-infectious. 3 The detection threshold for molecular tests is higher than culture, so patients with lower bacterial loads may still be infectious despite negative PCR results.

Do not discontinue isolation based solely on time on treatment. 1 Some patients are never infectious, while others with unrecognized drug-resistant TB may remain infectious for extended periods. The decision must incorporate clinical response, bacteriologic response, and drug susceptibility results.

HIV coinfection does not increase your infectiousness, though it may complicate diagnosis and treatment. 1