Diagnosis of latent tuberculosis

This is an automatically translated article.

Diagnosis of latent TB is a means of early detection of people at risk for TB. Especially those who have had time in contact with people with pulmonary tuberculosis, in order to have effective prevention and intervention measures.

1. Latent Tuberculosis

Latent tuberculosis is a healthy body carrying the TB bacteria in an inactivated state. These people have no symptoms, show no signs of illness, and cannot spread TB to others. However, if the immune system is weakened, it can lead to tuberculosis.
TB bacteria are transmitted from person to person through the air, when a person with pulmonary TB coughs, talks, sneezes,... If you breathe in the air containing TB bacteria, the bacteria will enter the lungs. However, the human immune system will stop and make the bacteria inactive and unable to cause disease. Some people have TB bacteria in a latent state in the body for life. Therefore, the immune system is important to keep TB bacteria inactive and prevent the bacteria from multiplying.
TB bacteria are not easily transmitted through the air. People with latent TB are those who have been in contact with someone with pulmonary TB. People who have been on effective TB treatment for more than 2 weeks cannot spread the disease. Therefore, people who need to be diagnosed with latent TB are people who live with or have been in close contact with a person with pulmonary tuberculosis for a period of time.

2. Diagnosis of latent tuberculosis

To identify a person with latent TB, the following conditions must be met:
Not having TB Can't spread to others Skin reaction test, positive blood test Sputum and secretion test is negative Therefore To diagnose a person with latent TB requires testing for TB bacteria and testing to confirm that they do not have TB.
2.1 Skin test The TB skin test, also known as the Mantoux reaction, is used to assess TB infection and guide the diagnosis of latent TB, tuberculosis. The person to be tested will be injected with 5 UI of PPD solution intradermally. A few weeks after the body is infected with TB bacteria, the lymphocytes become sensitive to TB bacilli. When tuberculin is injected in the skin, it will activate the sensitized lymphocytes, causing a delayed hypersensitivity reaction after 48-72 hours. clock.
After 2-3 days, the diameter of the reaction halo will be measured at the injection site. Positive results are calculated as follows:
Diameter 5mm for the following groups of patients: currently receiving immunosuppressive therapy, recent close contact with a person with tuberculosis, HIV infection, changes in the relative fibrous lesions. previous TB response. Diameter ≥ 10mm for the following groups of patients: healthcare workers, HIV-negative injecting drug users, kidney failure, diabetes mellitus, small bowel resection, gastrectomy. Diameter ≥ 15mm for patient groups: no risk of TB.

In addition, test results may be encountered such as:
False positive: atypical tuberculosis infection or previous BCG vaccination False negative: due to immunosuppression or new TB infection less than 8 weeks , a long history of previous TB infection, children under 6 months. 2.2 IGRA blood test IGRA testing is preferred for people who have received BCG vaccination. There are two types of IGRA
T-SPOT tests. TB: Quantification of IFN- QUANTIFERON-TB secreting T cells: measure IFN- If the test result is positive, it means that the patient has latent TB and needs to do other tests such as sputum sampling, chest x-ray to determine whether the patient has active tuberculosis.
In summary, the diagnosis of latent TB is a method to find TB bacteria in the body, for healthy people, who have not yet had symptoms, and especially those who have had time in contact with people with HIV infection. pulmonary tuberculosis. People who test positive, and have confirmed latent TB, are counseled on effective preventive measures, or prophylactic treatment, to reduce the risk of progression to active TB.
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