Tuberculosis: A Persistent Bacterial Infection

Tuberculosis, usually called TB, is a bacterial infection that can remain contained in the body or develop into active disease. It most often affects the lungs but can involve almost any organ. TB usually develops gradually and requires several antibiotics taken for months.

What tuberculosis is Tuberculosis, usually called TB, is caused by bacteria from the Mycobacterium tuberculosis complex. Mycobacterium tuberculosis causes most person to person TB. TB most often affects the lungs. It can also affect lymph nodes, bones, joints, the kidneys, the abdomen, the brain or other tissues. The bacteria grow more slowly than many common bacteria. Illness can therefore develop gradually, and treatment takes much longer than a standard course for many other infections. TB is curable in most people when the correct combination of medicines is taken for the full recommended course. Why TB can persist After TB bacteria enter the lungs, the immune system may remove them or contain them within organised areas of immune cells. Containment can prevent symptoms and tissue damage. Contained bacteria may remain in the body for months, years or decades. This state is called latent TB infection. In some people, the immune response does not contain the bacteria adequately. In others, contained infection later becomes active. The change from latent infection to active disease is sometimes called reactivation. Active disease can also develop relatively soon after a new infection. Latent TB and active TB are different A person with latent TB infection has TB bacteria in the body but no symptoms of TB disease. The bacteria are contained and are not causing active tissue damage. Latent TB is not infectious. Someone with latent TB cannot pass TB to family members, colleagues or other contacts. Latent TB may remain contained throughout life. However, it can develop into active TB, particularly when immune defence becomes weaker. Treatment for latent TB reduces the future risk of active disease. Active TB must be excluded before preventive treatment begins. A person with active TB has bacteria multiplying and causing disease. Active TB causes symptoms or other evidence of organ involvement and requires full multidrug treatment. Pulmonary and extrapulmonary TB Pulmonary TB affects the lungs or airways. This is the form most strongly associated with a prolonged cough and airborne transmission. Laryngeal TB affects the voice box and can also be highly infectious. It may cause hoarseness, throat symptoms or coughing. Extrapulmonary TB affects a site outside the lungs or main airways. Common sites include lymph nodes, bones, joints, the abdomen and the central nervous system. Extrapulmonary TB is not usually spread through the air unless pulmonary or laryngeal disease is also present. Rare situations involving exposed infected material require specialist infection control advice. Disseminated TB means infection has spread through the bloodstream to several areas. It is more likely when immune function is severely impaired and can be life threatening. How infectious TB spreads TB spreads through the air from someone with infectious pulmonary or laryngeal disease. Coughing, speaking or sneezing can release tiny particles containing bacteria. Transmission usually follows repeated, close or prolonged exposure, especially in poorly ventilated indoor spaces. Brief casual contact is much less likely to transmit TB. TB is not usually spread by sharing plates, touching surfaces, shaking hands or using the same toilet. Ordinary social contact should not be restricted beyond the advice given by the TB team. Not every person with active TB is infectious. Infectiousness depends on the disease site, the number of bacteria, coughing, laboratory findings and response to treatment. Effective treatment usually reduces infectiousness substantially. However, a person should not assume they are non infectious after a fixed number of days. The TB team decides when precautions can safely change. The prolonged symptom pattern Symptoms of active TB usually develop gradually. Pulmonary TB commonly causes a cough lasting longer than three weeks. The cough may be dry or produce phlegm. Some people cough up streaks of blood or a larger amount of blood. Other characteristic features include persistent fever, drenching night sweats, reduced appetite, unexplained weight loss, tiredness and feeling generally unwell. No symptom is unique to TB. Lung cancer, pneumonia, bronchiectasis and several other conditions can produce an overlapping pattern. A cough lasting more than three weeks deserves medical assessment even when the person does not feel severely unwell. Symptoms outside the lungs Lymph node TB may cause slowly enlarging, usually painless swellings, often in the neck. Nodes may occasionally become inflamed or drain through the skin. Bone or joint TB can cause persistent pain, swelling or reduced movement. Spinal TB can damage vertebrae and may compress the spinal cord. Abdominal TB may cause pain, swelling, altered bowel habit, fever or weight loss. Kidney or urinary TB can cause urinary symptoms or blood in urine. TB meningitis can cause severe headache, neck stiffness, sensitivity to light, vomiting, confusion, seizures or weakness. These patterns are not specific to TB. The suspected site determines which examinations, scans and samples are needed. Babies, children and vulnerable adults Young children may not develop the classic adult pattern. Possible features include persistent fever, tiredness, poor appetite, reduced activity and failure to gain weight or grow normally. Children younger than five years have a greater risk of progressing from infection to active disease. They are also more vulnerable to severe forms such as TB meningitis. Older adults may present with weight loss, weakness, reduced function or confusion rather than a prominent cough. Other illnesses can produce the same changes. People with impaired immune function may have unusual symptoms, disease outside the lungs or more rapid progression. A normal chest X ray or negative immune response test does not always settle the diagnosis. Anyone with suspected TB in a child or an immunocompromised person requires specialist assessment. Who has a higher risk Anyone can develop TB. Risk is increased by close contact with someone who has infectious pulmonary or laryngeal TB. Risk is also higher after living in or spending substantial time in a country where TB is more common. This reflects exposure patterns rather than nationality or ethnicity. Conditions or treatments that weaken immune defence increase the risk that latent infection becomes active. Examples include HIV, transplantation, chemotherapy and some biological medicines. Diabetes, chronic kidney disease, silicosis, low body weight and undernutrition can also increase risk. Babies and very young children are more vulnerable after exposure. Overcrowding, homelessness, imprisonment and difficulty accessing healthcare can increase exposure or delay diagnosis. Smoking, harmful alcohol use and drug dependence may add further risk. Risk factors guide testing and clinical suspicion. They do not prove infection and should never be used to stigmatise a person or community. How active TB is investigated A clinician asks about the duration of symptoms, contact with TB, previous treatment and time spent in places where TB is common. They also ask about immune suppression, HIV risk, medicines and social circumstances affecting care. The examination depends on the suspected site. For pulmonary disease, clinicians assess breathing, oxygen level, lymph nodes, weight and signs of wider illness. A chest X ray is a standard first investigation for suspected pulmonary TB. It may show changes that support TB, but no X ray pattern confirms the diagnosis alone. People who can produce phlegm usually provide several deep cough sputum samples. Laboratories examine these samples using microscopy, molecular tests and culture. Microscopy can identify acid fast bacteria but cannot always determine the exact species. Molecular tests can detect genetic material and may provide rapid information about rifampicin resistance. Culture remains important because it can confirm the organism and support detailed drug susceptibility testing. TB bacteria grow slowly, so final culture results may take several weeks. When disease is outside the lungs, clinicians may test tissue, fluid, urine, cerebrospinal fluid or another site specific sample. Imaging and biopsy can help locate disease and exclude alternative diagnoses. Tests for latent infection The Mantoux test places a small amount of tuberculin into the skin. The firm reaction is measured after a specified interval. An interferon gamma release assay, known as an IGRA, measures how immune cells respond to TB related proteins in a blood sample. These tests show immune sensitisation to TB bacteria. They do not prove that active disease is present and do not identify where TB is located. A positive test prompts assessment for active TB before latent treatment is considered. A negative result does not always exclude infection, particularly soon after exposure or when immune function is impaired. BCG vaccination can affect the Mantoux response. An IGRA is less affected by previous BCG vaccination, but it still requires clinical interpretation. Treating drug sensitive active TB Active TB is treated by a specialist TB service. Several antibiotics are used together because one medicine alone is more likely to leave resistant bacteria behind. For most drug sensitive active TB without central nervous system involvement, NICE recommends four medicines for the first two months. These are isoniazid, rifampicin, pyrazinamide and ethambutol. Isoniazid and rifampicin then continue for a further four months. This creates a standard minimum course of six months. TB involving the brain or meninges is generally treated for twelve months. Drug resistance, treatment interruption, intolerance or another clinical circumstance may also change the regimen or duration. Treatment is adjusted when drug susceptibility results become available. The TB team also checks for interactions with other medicines and monitors for adverse effects. Someone who feels better after several weeks is not cured. Remaining bacteria can multiply again if treatment is stopped too soon. Why adherence is essential Each medicine acts differently against the bacterial population. Taking the correct combination consistently makes cure more likely and reduces the chance of relapse. Missing repeated doses or stopping treatment early can allow disease to return. It can also select bacteria that are harder to treat. Adherence problems are not simply personal failure. Side effects, unstable housing, work, transport, language, memory, stigma and competing responsibilities can all disrupt treatment. Everyone with active TB should have a named case manager. The plan may include reminders, practical support, translated information and help with transport or housing. Directly observed therapy means a trained person supports and records the taking of doses. It is used selectively when enhanced support is needed, not as a punishment. New symptoms or possible medicine side effects should be discussed promptly with the TB team. Medicines should not be stopped independently unless emergency medical advice requires it. Treating latent TB infection Latent TB treatment aims to kill contained bacteria before they cause active disease. It does not treat symptoms because latent TB causes none. Treatment is offered after active disease has been excluded. The decision considers age, recent exposure, immune function, liver risk, medicine interactions and the likelihood of future progression. Common UK regimens last three or six months. Fewer medicines are used than for active disease because the bacterial burden and clinical situation are different. Completing latent treatment lowers the future risk of active TB but does not create absolute lifelong protection. A person can still be exposed to TB again. Drug resistant TB Drug resistant TB means that one or more standard medicines no longer work against the bacterial strain. Resistance may already be present when infection is acquired. Resistance can also emerge when an inadequate drug combination is used or treatment is taken inconsistently. It is therefore another reason to use several drugs and complete treatment. Multidrug resistant TB, known as MDR TB, is resistant to at least isoniazid and rifampicin. Rifampicin resistant TB is also treated as a major specialist concern. Drug resistant disease requires rapid molecular testing, detailed susceptibility testing and specialist multidisciplinary care. Infection control precautions may need to continue longer. Treatment is individualised and may involve different medicines, closer monitoring and a longer or specially selected regimen. Modern all oral regimens are possible for some people, but they are not interchangeable or suitable for every resistance pattern. Drug resistant TB remains treatable. It should be understood as a microbiological problem requiring specialist care, not as a moral judgement about the person affected. Notification and contact tracing All suspected and confirmed active TB is legally notifiable through the relevant national public health system. Notification allows TB services and public health teams to coordinate care and reduce further transmission. Close contacts of someone with pulmonary or laryngeal TB are assessed without unnecessary delay. Symptomatic contacts are investigated for active disease. Contacts without symptoms may be tested for latent infection after active TB has been excluded. Children and people with weakened immune systems may need particularly prompt assessment. Not every colleague, classmate or passenger is automatically a close contact. The team considers proximity, duration, ventilation, infectiousness and the contact's vulnerability. Contact tracing is confidential and supportive. It identifies people who may benefit from testing, preventive treatment or BCG vaccination. BCG vaccination The Bacillus Calmette Guérin vaccine, called BCG, reduces the risk of TB and is especially valuable against severe childhood forms such as TB meningitis. BCG does not prevent every infection or every case of pulmonary TB. A vaccinated person with a prolonged concerning illness still needs assessment. The UK uses a targeted programme rather than vaccinating everyone. It is offered to eligible babies, children and selected adults with increased exposure risk. Eligibility depends on age, household or occupational exposure, residence and links with countries or areas where TB is more common. Current NHS and UKHSA guidance should be used because criteria can change. Recovery and follow up Symptoms often improve during treatment before all bacteria have been eradicated. Cough, fatigue, appetite and weight may recover at different rates. The TB team reviews symptoms, medicine tolerance and adherence. Sputum testing, blood tests, imaging or other investigations may be repeated when clinically needed. Some people are left with lung scarring, reduced exercise tolerance, chronic pain or neurological problems after severe extrapulmonary disease. Rehabilitation and specialist follow up may be required. TB can also affect employment, housing, finances and emotional wellbeing. Social and psychological support can be part of effective medical care. Treatment for active and latent TB is available through NHS TB services, and people should seek care without fear of blame or stigma. What this lesson should not be used for This lesson cannot determine whether a prolonged cough, night sweats or weight loss is caused by TB. These features have several possible explanations. A Mantoux or IGRA result cannot diagnose active TB by itself. Do not use this lesson to select medicines, stop isolation precautions or decide that someone is no longer infectious. Seek professional assessment for a cough lasting more than three weeks, unexplained weight loss, persistent night sweats or close contact with infectious TB.

Latent TB means bacteria are contained, cause no symptoms and cannot spread to others. Active TB means bacteria are causing disease and may be infectious when the lungs or larynx are involved. Cure usually requires several antibiotics taken consistently for at least six months, with specialist testing and longer or different treatment when resistance is present.