Tuberculosis

Tuberculosis (TB) is a bacterial infection that commonly affects your lungs but may also affect other areas of your body, like your spine, brain or kidneys. It is a serious disease that may cause a person to become very sick if it is not treated properly.

Not everyone who is infected with TB gets sick. They may have inactive tuberculosis, or latent TB, if they are exposed to the TB bacteria but exhibit no symptoms. Some people may have latent TB throughout their lifetime, without it ever developing into active TB. However, if your immune system becomes weakened, you may develop active TB.

Understanding How TB Infection Develops

When TB bacteria are first inhaled into the lungs, the immune system usually responds quickly, sending specialised cells to surround and contain the bacteria within a small, wall-like structure. In most healthy people, this response is effective enough to stop the bacteria from causing illness, but it does not always eliminate them completely. Instead, the bacteria can remain alive but inactive within this contained structure for years, or even a lifetime, without causing any symptoms — this is what is meant by latent TB.

Active TB develops when this containment breaks down, allowing the bacteria to multiply and cause tissue damage. This can happen soon after the initial infection, particularly in those with a weaker immune system, or it can happen many years later, when something — illness, medication, ageing or other health conditions — weakens the immune system's ability to keep the dormant bacteria under control.

Latent TB vs Active TB

Causes of Tuberculosis

• Breathing in airborne bacteria: TB can spread through the air when a person with active TB in the lungs or throat coughs, sneezes, talks, sings or laughs. The bacteria can be released into the air and inhaled by people nearby.
• Prolonged or close contact with someone who has active TB: TB is more likely to spread through prolonged or repeated close contact with someone who has contagious active TB. Brief, casual contact, such as passing someone on the street, generally carries a much lower risk of transmission.

If not treated early, infection with TB can cause permanent lung damage and can spread to other parts of the body, including the intestine, brain and central nervous system.

Risk Factors of Tuberculosis

You may be at risk of getting active TB if you:

• Have an impaired or weakened immune system: Conditions such as HIV, certain autoimmune diseases, or medications that suppress the immune system reduce the body's ability to keep latent TB bacteria contained, significantly raising the risk that a dormant infection will become active.
• Have a chronic condition (kidney disease, diabetes, etc.): Chronic conditions such as kidney disease and diabetes place ongoing strain on the immune system and are well-established risk factors for TB reactivation.
• Have received an organ transplant: The medications required to prevent organ rejection after a transplant work by suppressing the immune system, which can also allow latent TB bacteria to become active.
• Are in chemotherapy for cancer: Chemotherapy affects the immune system's ability to function normally, similarly increasing the risk that a contained TB infection could progress to active disease.
• Have close or prolonged contact with someone who has active TB: Living or working closely with someone who has active, untreated pulmonary TB — such as in the same household, or in crowded, poorly ventilated settings like dormitories or shelters — increases the likelihood of exposure to the bacteria in the first place.
• Are malnourished: Malnutrition weakens the immune system generally, and has long been recognised as a significant risk factor for TB reactivation in populations where it is common.

Symptoms of Tuberculosis

If you have latent TB, you won't exhibit symptoms, but you may have a positive TB test. Symptoms of active TB include:

• Bad cough lasting more than two weeks: A cough that persists for more than two weeks is one of the hallmark symptoms of active pulmonary TB and is often what first prompts someone to seek medical evaluation.
• Chest pain: Ongoing inflammation and irritation within the lungs or the lining around them can cause a dull ache or sharper pain, particularly with deep breathing or coughing.
• Coughing up blood or blood-stained phlegm: This occurs when TB has caused enough damage to the lung tissue or its blood vessels to cause bleeding, and is generally considered a sign of more significant lung involvement.
• Fatigue: A pervasive, ongoing tiredness that does not improve with rest is common in active TB, related to the body's sustained immune response to the infection.
• Weakness: A general sense of reduced physical strength and energy often accompanies the fatigue and other systemic symptoms of active TB.
• Loss of appetite: Active infection commonly suppresses appetite, which, combined with the body's increased energy demands while fighting the infection, contributes to the weight loss also seen with TB.
• Weight loss: Progressive, unintentional weight loss is a classic feature of active TB and reflects the combination of reduced appetite and the metabolic toll of a sustained infection.
• Chills: Periods of feeling unusually cold, sometimes with shivering, often accompany the fever associated with active TB.
• Fever: A persistent or recurring fever reflects the body's ongoing immune response to the active infection.
• Night sweats: Heavy sweating during sleep, sometimes significant enough to require changing bedding or sleepwear, is a well-recognised and fairly specific symptom of active TB.

Possible Complications of Untreated Tuberculosis

Left untreated, active TB can lead to serious and sometimes irreversible complications, which is why completing appropriate treatment is so important once TB is diagnosed.

• Permanent lung damage: Ongoing, untreated infection can destroy lung tissue over time, permanently reducing lung capacity and function even after the infection is eventually brought under control.
• Spread to other organs: TB bacteria can travel through the bloodstream to seed infection in the spine, joints, kidneys, lymph nodes, or, in serious cases, the brain and its surrounding membranes, each requiring its own course of extended treatment.
• Miliary TB: A widespread, severe form of TB in which the bacteria spread throughout the bloodstream to multiple organs simultaneously, more common in those with a significantly weakened immune system and requiring urgent, intensive treatment.
• Drug-resistant TB: Incomplete or inconsistent treatment allows surviving bacteria to develop resistance to standard medications, resulting in multidrug-resistant TB, which is considerably harder, longer and more complex to treat successfully.

These risks underscore why active TB is treated as a serious, notifiable condition requiring a complete, supervised course of medication, rather than one where treatment can be stopped once symptoms start to improve.

How Tuberculosis is Diagnosed

• TB Skin Test (Mantoux Test): A small amount of testing fluid is injected just under the skin of the forearm, and the site is checked 48 to 72 hours later for a reaction, which can indicate past exposure to TB bacteria.
• Interferon-Gamma Release Assay (Blood Test): A blood test that measures the immune system's response to TB bacteria, offering an alternative to the skin test that is not affected by prior BCG vaccination.
• Chest X-ray: Your doctor may perform an X-ray, which can show where TB has damaged your lungs, including patterns typical of active infection or scarring from a past infection.
• Sputum Test: Samples of your phlegm will be tested to check for the presence of TB germs, typically through microscopic examination and culture. This confirms active infection and can also show whether the bacteria are resistant to particular medications.
• Molecular (Rapid) Testing: Newer laboratory tests can detect the genetic material of TB bacteria directly from a sputum sample, often providing a result within hours and giving early information about drug resistance, considerably faster than traditional culture methods.

Preventing Tuberculosis

You can reduce your risk of catching TB by:

• Washing your hands often: Regular handwashing reduces the general spread of many infections and forms part of good overall hygiene practice, even though TB itself spreads mainly through airborne droplets rather than surface contact.
• Avoiding close contact with people who are suffering from TB: Reducing prolonged, close-range exposure to someone with known active, untreated TB lowers the chance of inhaling enough bacteria to become infected.
• Making sure you take all your medication as prescribed: Completing every dose of a prescribed TB treatment or preventive course, exactly as directed, is one of the most important ways to prevent the infection from persisting, relapsing, or developing drug resistance.
• Ensuring proper ventilation in rooms: Good airflow helps disperse and dilute airborne TB bacteria, reducing the concentration a person in the same room is exposed to over time.
• Using personal protective equipment: Masks and other appropriate protective equipment reduce the risk of inhaling or spreading infectious droplets, particularly important for those caring for or living with someone with active TB.

If you are diagnosed with TB, avoid going to crowded places while still contagious, and always cough or sneeze into a tissue before throwing it into a rubbish bin. Also ensure that any household surfaces that come into contact with you are cleaned with disinfectant. In many countries, a BCG vaccine is also given, usually in infancy, which offers meaningful protection against the most severe forms of childhood TB, though its protection against typical adult pulmonary TB is more limited.