One of the most important things to understand about tuberculosis is that infection and disease are not the same thing. TB exists in two distinct states, and the difference between them has significant implications for symptoms, contagiousness, and health.

Latent TB infection occurs when TB bacteria enter the body but the immune system successfully contains them, preventing them from multiplying and causing illness. People with latent TB infection feel completely well, have no symptoms, and cannot spread TB to others. The bacteria are essentially dormant, walled off by the immune system. However, latent TB is not the same as being rid of the bacteria. Under certain conditions, particularly if the immune system becomes weakened, the bacteria can reactivate and progress to active disease.

Active TB disease means the bacteria are multiplying, causing symptoms, and in most cases, capable of being spread to others. Active TB most commonly affects the lungs, but it can also involve the kidneys, spine, brain, lymph nodes, and other organs. Without appropriate medical care, active TB can cause serious harm and, in some cases, be life-threatening.

The distinction between these two states is central to how TB is evaluated and managed. Testing for TB infection is not the same as testing for active TB disease, and both require different approaches.

TB spreads through the air, not through casual physical contact. This is an important distinction because it affects both how transmission actually happens and what does not put people at risk.

When a person with active TB disease of the lungs or throat coughs, sneezes, speaks, laughs, or sings, they can release tiny droplet nuclei containing TB bacteria into the air. These particles are so small that they can remain suspended in the air for hours, particularly in enclosed spaces with poor ventilation. A person nearby who breathes in those particles may inhale the bacteria.

TB is not spread through:

• Shaking hands or physical touch of any kind
• Sharing food, drinks, or utensils
• Touching surfaces such as bedding, toilet seats, or doorknobs
• Kissing or other casual contact

Close, prolonged contact with a person who has active, contagious TB in an enclosed space presents the greatest risk of transmission. Occasional or brief contact is much less likely to result in infection.

It is also worth noting that not everyone with TB is contagious. People with latent TB infection cannot spread TB to others. Even among those with active TB disease, infectiousness varies depending on the location of the disease in the body, the severity of the illness, and other factors.

Symptoms of TB depend on where in the body the bacteria are active. The most common form is pulmonary TB, meaning TB in the lungs, and it produces a recognizable set of symptoms. One of the more challenging aspects of TB is that symptoms can be gradual and mild for a long time, making it easy to overlook or attribute to another cause.

Common symptoms of active pulmonary TB include:

• A persistent cough lasting three weeks or longer, which may produce mucus or, in some cases, blood
• Chest pain or discomfort when breathing or coughing
• Unintentional weight loss that occurs without changes in diet or activity
• Fatigue and a general sense of weakness or low energy
• Fever, which may be low-grade and easy to dismiss
• Night sweats that are drenching and disruptive to sleep
• Chills that may accompany the fever

When TB affects parts of the body other than the lungs, symptoms reflect the organ or system involved. TB of the spine may cause back pain. TB involving the kidneys may produce blood in the urine. TB affecting the brain or its surrounding tissues can cause headaches, confusion, or neurological changes. TB of the lymph nodes may produce swollen, tender glands, particularly in the neck.

Because many of these symptoms overlap with other conditions, TB is not always the first thing considered. A persistent cough combined with weight loss, night sweats, and fatigue is a combination that warrants medical evaluation, especially in anyone with known risk factors.

TB risk is helpful to think about in two categories: risk of being exposed to TB bacteria in the first place, and risk of progressing from latent infection to active disease once exposed.

Those at higher risk of exposure include:

• Close contacts of someone with active, contagious TB, such as household members or frequent companions
• People born in or who frequently travel to countries where TB rates are higher, including parts of sub-Saharan Africa, South and Southeast Asia, Eastern Europe, and Latin America
• People who live or work in congregate settings where TB can spread more easily, such as homeless shelters, correctional facilities, long-term care facilities, or certain healthcare environments

Those at higher risk of progressing from latent infection to active disease include:

• People living with HIV, for whom weakened immune defense makes progression significantly more likely
• People with diabetes, which impairs immune function in ways that increase susceptibility to active TB
• People who use tobacco, as smoking is associated with increased risk of both TB infection and active disease
• People with certain medical conditions that affect the immune system, including kidney disease, certain cancers, and conditions requiring immune-suppressing medications
• Children under 5 and older adults, both of whom tend to have less robust immune responses
• People who have experienced significant malnutrition, which undermines immune defense

Having one or more of these risk factors does not mean TB is inevitable, but it does mean that awareness, screening conversations with a healthcare provider, and prompt evaluation of concerning symptoms are all the more important.

Diagnosing TB is a step-by-step process that aims to answer two distinct questions: whether a person has been infected with TB bacteria at some point, and whether that infection has progressed to active TB disease now.

The main tools used in evaluation include:

• TB skin test (tuberculin skin test or TST), in which a small amount of a protein derived from TB bacteria is injected just under the skin of the forearm. After 48 to 72 hours, the size of any reaction at the site is measured. A positive result indicates the immune system has encountered TB bacteria but does not confirm active disease.
• TB blood tests (interferon-gamma release assays or IGRAs), which measure the immune system's response to TB proteins in a blood sample. These tests are an alternative to the skin test and are often preferred in certain populations, including people who have received the BCG vaccine.
• Chest X-ray, which is used to look for changes in the lungs that may indicate TB disease. An abnormal X-ray finding in someone with a positive TB test raises concern for active disease.
• Sputum tests, in which samples of mucus coughed up from deep in the lungs are examined under a microscope and cultured to detect TB bacteria. A positive culture confirms active TB disease and is the gold standard for diagnosis.
• Additional imaging and testing may be used when TB outside the lungs is suspected, including CT scans, biopsies, and tests of urine or spinal fluid depending on the area of concern.

A positive skin test or blood test alone does not mean a person has active TB disease. It means the immune system has responded to TB bacteria at some point, which may represent latent infection and warrants further evaluation.

When active TB disease goes unaddressed, it can cause serious and lasting harm. The complications that may arise depend on where in the body the disease is active and how far it has progressed.

Pulmonary TB can lead to:

• Scarring and long-term lung damage that affects breathing even after the infection has been addressed
• Coughing up significant amounts of blood (hemoptysis), which can range from mild to severe
• Pleural complications, including fluid buildup or infection in the space surrounding the lungs

When TB spreads beyond the lungs, serious complications become possible in multiple organ systems:

• Miliary TB is a severe form in which bacteria spread through the bloodstream and seed multiple organs simultaneously, including the lungs, liver, spleen, and bone marrow
• TB meningitis involves infection of the membranes surrounding the brain and spinal cord and can cause permanent neurological damage
• Spinal TB (also called Pott's disease) can damage vertebrae and, in severe cases, lead to spinal deformity or compression of the spinal cord
• Kidney damage from TB involvement of the urinary tract can affect long-term kidney function

The good news is that TB is a treatable and curable condition. The risk of complications is substantially reduced when TB is identified early and medical care is sought promptly.

Tuberculosis carries significant stigma in many communities, and that stigma is often fueled by misconceptions. Clearing up some of the most common myths helps both reduce fear and encourage people to seek care without shame.

• "TB is a disease of the past." TB remains one of the most significant infectious diseases in the world today and continues to affect millions of people each year globally, including in developed countries.
• "You can get TB from casual contact." TB does not spread through shaking hands, sharing food, touching surfaces, or brief encounters. It requires prolonged exposure to the air in a shared space with a contagious person.
• "If I had TB, I would know it." Latent TB infection causes no symptoms at all. Even active TB can be mild and gradual in its early stages, which is why people with risk factors are encouraged to discuss screening with their provider rather than waiting for obvious symptoms.
• "Only people who are poor or homeless get TB." While certain social and environmental factors increase exposure risk, TB can affect people across all demographics. Risk factors include immune status, travel history, and close contact with an infected person, none of which are limited to any single group.
• "TB always affects the lungs." While pulmonary TB is the most common form, TB can affect virtually any organ in the body, including the lymph nodes, spine, kidneys, and brain.

You should speak with a healthcare provider about TB evaluation if you have been in close contact with someone who has been diagnosed with active TB, if you have traveled to or lived in a region where TB is more prevalent, or if you live or work in a setting with higher TB exposure risk, such as a healthcare facility, shelter, or correctional environment.

You should seek medical evaluation promptly if you have symptoms consistent with active TB, particularly a persistent cough lasting three weeks or more, unexplained weight loss, night sweats, fatigue, and fever occurring together. These symptoms warrant evaluation regardless of whether you have a known exposure history, especially if you have any of the risk factors that increase the likelihood of progression.

If you have already been told you have latent TB infection, staying in contact with your healthcare provider is important. Latent TB is not a cause for alarm, but it does warrant monitoring and, in some cases, a conversation about steps that may reduce the risk of it progressing to active disease.

TB is both preventable and curable. The most important thing anyone can do when TB is a possibility is to seek evaluation early rather than waiting for symptoms to worsen.