Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis, which most commonly attacks the lungs. It represents a significant global health challenge, causing millions of illnesses and deaths annually worldwide. As an airborne infection, TB transmission requires dedicated public health and individual strategies to interrupt the spread of the bacteria. These strategies detail how individuals and medical systems work together to stop the transmission of this pathogen.
Understanding How Tuberculosis Spreads
Tuberculosis spreads through the air when a person with active pulmonary disease expels the bacteria into the environment. These bacteria are contained within microscopic droplets, released when an infected person coughs, sneezes, speaks, or sings. Anyone nearby can inhale these particles, allowing the bacteria to settle in the lungs and potentially initiate an infection. Only individuals with active TB disease in the lungs or throat are considered contagious. The majority of people infected develop Latent TB Infection (LTBI), where the immune system contains the germs in an inactive state, meaning they cannot spread the bacteria to others.
Personal and Household Infection Control Measures
Controlling the release of bacteria from an infectious individual is the most immediate way to prevent transmission in homes and communities. This involves practicing excellent respiratory hygiene, such as covering the mouth and nose with a tissue when coughing or sneezing. Prompt disposal of tissues and routine hand washing reduces the risk of environmental contamination.
For individuals diagnosed with active, transmissible TB, temporary isolation is necessary to break the chain of infection. This usually involves staying home and limiting visitors until a healthcare provider confirms the person is non-infectious. Typically, a patient becomes non-contagious after two to three weeks of effective anti-tuberculosis medication.
Environmental controls are important, particularly in shared indoor spaces. Maximizing ventilation by opening windows or using exhaust fans helps to quickly dilute and remove airborne particles from the air. In high-risk clinical settings, specialized measures like negative pressure rooms, HEPA filtration systems, and ultraviolet germicidal irradiation (UVGI) are employed to clean the air. When an infectious patient must leave isolation, they should wear a surgical mask to contain expelled particles, while healthcare workers should wear a fit-tested N95 respirator for personal protection.
Medical Strategies for Preventing Active Disease
Preventing the progression from non-transmissible LTBI to transmissible active TB disease is a medical strategy for transmission control. Treating LTBI eliminates the dormant bacteria, preventing the individual from developing a contagious illness. Without treatment, approximately 5–10% of infected people will develop active TB disease, with the risk highest in the first two years after infection.
Modern treatment regimens for LTBI are significantly shorter and better tolerated than past standards. Options include a three-month course of weekly isoniazid and rifapentine, or a four-month daily course of rifampin. Completing the full course of therapy is necessary to ensure all dormant bacteria are eradicated and to prevent the emergence of drug-resistant strains.
The Bacillus Calmette-Guérin (BCG) vaccine is widely used in countries with a high burden of TB. Its primary role is to protect infants and young children from the most severe forms of the disease, such as miliary TB and TB meningitis. Since BCG offers variable protection against adult pulmonary TB (the most common and transmissible form), vaccination alone is not a reliable strategy for preventing overall spread.
The Role of Testing and Screening
Identifying infected individuals is a prevention method because transmission cannot be stopped if the source is unknown. Screening focuses on populations at high risk of exposure or progression to active disease. These groups include:
- Close contacts of patients with active TB.
- Healthcare workers.
- Immunocompromised individuals.
- Those born in or frequently traveling to countries with a high prevalence of the disease.
Two primary tests detect M. tuberculosis infection: the Tuberculin Skin Test (TST) and Interferon-Gamma Release Assays (IGRAs). IGRAs are often preferred because they are not affected by prior BCG vaccination and require only a single patient visit. A positive result indicates infection but does not differentiate between non-contagious LTBI and contagious active disease.
Following a positive screening test, a medical evaluation, including a symptom assessment and a chest X-ray, is required to rule out active TB disease. Prompt diagnosis and initiation of a multi-drug treatment regimen for active disease render a patient non-infectious and halt community transmission. Early identification allows for the timely start of LTBI treatment in high-risk contacts, preventing their transition to a transmissible state.