Latent Tuberculosis Infection: Symptoms, Causes & Treatment

Latent tuberculosis infection (LTBI) is a state where Mycobacterium tuberculosis bacteria are present in the body but remain dormant or inactive, meaning no active disease symptoms or lung lesions are present. People with LTBI feel healthy and cannot transmit the infection to others, but they carry a 5-10% lifetime risk of developing active TB, especially if their immune system weakens.

LTBI cases became widely recognized in the 1990s following advances in diagnostic tests such as tuberculin skin test (TST) and interferon-gamma release assays (IGRA). Approximately one-quarter of the world's population has latent TB infection. In Jordan and the Middle East region, infection rates are moderate to high, particularly among migrants, refugees, and healthcare workers.

Preventive treatment for latent TB reduces the risk of progression to active disease by up to 90%, making early detection and treatment a crucial public health strategy to prevent TB transmission in communities.

Latent TB infection is defined by the complete absence of symptoms; the infected person feels completely healthy with no disease signs. Therefore, latent TB can only be detected through medical tests recommended for high-risk groups or people exposed to active TB patients.

• No cough: Unlike active TB, there is no persistent cough lasting more than 3 weeks.
• No fever: Body temperature remains normal; no evening or morning fever.
• No night sweats: The person does not wake up drenched in sweat at night.
• No weight loss: Weight remains stable without unexplained loss.
• No chest pain: No discomfort when breathing or coughing.
• Normal energy and activity: The person performs daily activities normally without fatigue.
• No clinical signs: Physical examination reveals no abnormal lung sounds or signs of disease in any organ.

• Exposure to active TB patient: Inhalation of airborne droplets containing TB bacteria from coughing or sneezing of a person with active pulmonary TB, leading to bacterial colonization in the lungs without disease development.
• Occupational exposure in hospitals: Healthcare workers are directly exposed to TB bacteria when treating patients without adequate infection control precautions.
• Living with an active TB patient: Family members and close contacts of active TB patients over extended periods have increased risk of latent infection.
• Exposure in crowded institutions: Prisons, shelters, and refugee camps where ventilation is poor and sanitation standards are low.
• Migration from high-burden regions: People from African and Asian countries with high TB prevalence may carry latent infection.
• Incomplete previous TB treatment: Individuals who were treated for active TB but did not complete therapy adequately may retain dormant bacteria.

• Immunocompromise (HIV/AIDS): People with HIV/AIDS, especially those not on antiretroviral therapy, have much higher risk of progressing from latent to active TB.
• Diabetes mellitus: Elevated blood sugar weakens immune function and increases disease progression risk.
• Chronic kidney disease: Renal failure impairs immunity and infection control capacity.
• Immunosuppressive medications: Drugs used to treat autoimmune diseases or prevent organ transplant rejection increase TB risk.
• Young age (under 5 years): Infants and young children have weaker immunity and higher risk of developing active TB.
• Malnutrition and poverty: Deficiency of essential vitamins and minerals reduces immune function.
• Smoking and alcohol consumption: Weaken immunity and increase disease progression risk.
• Pregnancy and lactation: Hormonal changes affect immunity and increase progression risk.

Diagnosis of latent TB infection relies on specialized tests rather than clinical symptoms, as infected individuals are asymptomatic. Testing is recommended for exposed or at-risk individuals. Two main globally recognized diagnostic approaches exist.

• Tuberculin Skin Test (Mantoux Test): A small amount of PPD (Purified Protein Derivative) is injected intradermally on the forearm. After 48-72 hours, induration (swelling and redness) is measured in millimeters. Results are classified as positive based on size and patient risk status (5 mm for immunocompromised, 10 mm for healthcare workers, 15 mm for general population).
• Interferon-Gamma Release Assays (IGRA) - such as QuantiFERON-Gold: A blood test measuring immune response to TB-specific antigens. More accurate than Mantoux, especially in BCG-vaccinated or immunocompromised individuals. Positive result indicates TB infection.
• Additional tests (excluding active TB): After confirming latent TB, active disease must be ruled out by: chest X-ray (should be normal or without active findings) and complete clinical examination (no cough or symptoms).
• Other blood tests: Complete blood count (CBC) and liver/kidney function tests may be ordered before starting preventive therapy.

Medications

• Isoniazid for 9 months: First-line and globally recommended option. Taken orally daily at 5 mg/kg (typically 300 mg for adults). Reduces risk of progression to active TB by 90%.
• Rifampicin for 4 months: Faster alternative to isoniazid, especially for individuals who cannot tolerate long-term isoniazid or experience side effects.
• Isoniazid + Rifampicin for 3-4 months: Effective combination faster than isoniazid alone, suitable for high-risk groups.
• Weekly isoniazid doses: Shortened program of 12 weekly doses under direct medical supervision, useful for non-adherent patients.
• Side effect monitoring: Liver function tests required before starting and during treatment, especially in elderly or liver disease patients, as hepatitis occurs in 1-2% of cases.

Procedures/Surgery

• No surgery required: Latent TB does not require surgical intervention. Treatment is purely preventive and medication-based.
• Regular follow-up: Scheduled visits (monthly or bimonthly) to assess treatment adherence, side effects, and patient complaints.

Lifestyle Changes

• Avoid alcohol: Alcohol increases hepatitis risk with isoniazid and may affect treatment adherence.
• Proper nutrition: Eat balanced diet rich in vitamins, especially vitamin B6 (found in poultry, meat, and legumes), as isoniazid may cause deficiency.
• Rest and sleep: Get 7-8 hours daily sleep to boost immunity and help body fight dormant bacteria.
• Avoid smoking: Smoking weakens immunity and increases TB progression risk.
• Stress management: Psychological stress weakens immunity; practice relaxation and calming activities.

• Progression to active TB (in 5-10% of untreated cases): Without treatment, latent TB may develop into active pulmonary or extrapulmonary TB with serious symptoms. Progression can occur at any time, especially with immunosuppression.
• Extrapulmonary TB: Dormant bacteria may spread to other organs like bones, joints, kidneys, brain, and lymph nodes, causing serious complications.
• TB Meningitis: One of TB's most dangerous complications, especially in children and immunocompromised individuals. Can cause acute meningitis and lead to disability or death.
• Drug-induced hepatitis (from preventive therapy): Although treatment is safe, 1-2% of patients may experience drug-induced hepatitis (especially from isoniazid), but this is rare with proper medical monitoring.
• Delayed diagnosis and treatment: If latent TB remains undetected, the person unknowingly carries infection and may transmit it if progression to active TB occurs.
• Drug resistance: Rarely, TB bacteria may develop resistance to preventive medications (MDR-TB), especially with non-adherence to complete treatment.

• Early detection and testing: At-risk individuals (healthcare workers, close contacts of active TB patients, migrants from high-prevalence countries, immunocompromised people) should be tested regularly for latent TB.
• Isolation and protection from active TB: When active TB is diagnosed in household or workplace, provide safe, well-ventilated environment and isolate the patient to prevent transmission.
• Complete preventive treatment adherence: Those diagnosed with latent TB must complete preventive therapy (9 months isoniazid or alternatives) fully, even if tired or forgetful about medications.
• Hygiene and public health compliance: Regular handwashing, avoiding sneezing/coughing on others, using tissues when coughing.
• Improve living conditions: Improve ventilation in homes and crowded places, provide healthy non-crowded housing, and improve general sanitation.
• Strengthen immunity: Eat balanced healthy diet, get adequate sleep, exercise moderately, avoid smoking and alcohol.
• BCG vaccination: In high TB burden countries, BCG vaccine is given to infants as primary protection against severe TB.
• Regular medical follow-up: People treated for latent TB should remain under medical supervision to ensure no disease progression.