Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. The infection most often affects the lungs, but it can spread to other parts of the body. TB germs are transmitted through the air when a person with active disease coughs, speaks, or sings, releasing tiny droplets that others can inhale. While many people have latent TB—meaning the bacteria are present but inactive—certain circumstances and health conditions increase the probability of developing the active, symptomatic disease. Understanding these factors is necessary for prevention and early detection.
Risk Associated with Exposure and Geography
The likelihood of encountering Mycobacterium tuberculosis is influenced by proximity to an infectious individual and geographic location. Infection involves close, prolonged contact with someone who has active, untreated pulmonary TB disease. This risk is particularly elevated for household members, immediate family, and co-workers who share indoor airspaces with an infectious person for extended periods.
Certain environments facilitate transmission due to overcrowding and poor ventilation. People living or working in large group settings, such as homeless shelters, correctional facilities, and nursing homes, face increased exposure risk. These settings often combine close quarters with populations that may have limited access to healthcare, allowing the disease to spread easily. Healthcare professionals are also at an increased occupational risk because they work directly with high-risk patients.
The risk of exposure varies significantly across the globe, correlating with areas where TB is highly prevalent. Individuals born in or frequently traveling to countries with a high burden of TB disease face elevated risk. High-prevalence areas include countries in Southeast Asia, Sub-Saharan Africa, and parts of Latin America. Higher rates in these regions are often linked to challenges in public health programs, limited diagnostic resources, and socioeconomic factors.
Underlying Medical Conditions and Weakened Immunity
The body’s ability to contain a latent TB infection and prevent its progression to active disease depends on the strength of the immune system. Conditions that compromise immune function raise the risk of active TB. Human Immunodeficiency Virus (HIV) infection is the single most impactful risk factor globally.
HIV directly attacks and destroys CD4 T-lymphocytes, the immune cells that organize the body’s defense against the TB bacteria. This destruction makes the immune system unable to wall off the bacteria, increasing the risk of developing active TB disease by a factor of up to 20 to 30 times compared to people without HIV.
Chronic diseases that cause systemic immune dysfunction also compromise the body’s defenses against TB. Diabetes mellitus, for example, is associated with an increased risk of developing active TB disease. High blood sugar levels impair the function of T-cells and macrophages, the primary cells responsible for containing the TB bacteria. Severe kidney disease, certain cancers, and malnutrition also dampen the immune response, making progression to active TB more likely.
The use of certain medications designed to suppress the immune system also creates vulnerability. Patients receiving immunosuppressive therapies for autoimmune disorders, such as corticosteroids or TNF-alpha inhibitors used to treat conditions like rheumatoid arthritis or Crohn’s disease, face an increased risk. These drugs interfere with the cellular processes the body uses to keep latent TB inactive. Organ transplant recipients, who must take anti-rejection medications, are also placed at a higher risk for TB disease.
Demographic and Socioeconomic Risk Factors
Demographic characteristics and socioeconomic circumstances correlate with an individual’s overall risk profile for TB. Age is a factor, as the immune system is weakest at the extremes of life. Infants and young children, whose immune systems are still developing, are less able to contain the infection, putting them at greater risk of developing severe forms of the disease. The elderly are also at increased risk because their immune defenses naturally wane with age, which can lead to the reactivation of a latent infection.
Substance abuse, specifically heavy alcohol consumption and injection drug use, acts as a compound risk factor. These behaviors often lead to poor nutrition and can be associated with unstable housing and delayed healthcare access. Malnutrition and low body weight alone hinder the body’s immune response to the bacteria.
Poverty and low socioeconomic status contribute to the spread of TB by creating environments where transmission is more likely and treatment is less accessible. Overcrowded housing, inadequate ventilation, and a lack of basic sanitation services are associated with higher rates of TB infection in a community. Financial barriers and limited access to quality healthcare often result in delayed diagnosis and incomplete treatment, allowing the disease to progress and spread.