[Health Check] South Korea Ranks 1st in OECD Tuberculosis Prevalence... The Cause Is 'Latent Tuberculosis'

Elderly and Patients with Underlying Conditions at Risk Due to Low Immunity
Early Detection Required Through Antigen Testing

[Photo by Clipart Korea]

March 24th is observed annually as 'World Tuberculosis Day.' It is a day designated by the World Health Organization (WHO) to raise awareness about the causes and importance of managing tuberculosis. Tuberculosis is one of the three major diseases prioritized by WHO, along with AIDS and malaria. According to WHO's 'Global Tuberculosis Report 2022,' the number of tuberculosis patients worldwide has increased for two consecutive years. The number of deaths also rose by about 100,000 within a year, from 1.5 million in 2020. Although known as a disease prevalent in developing countries, the recent surge in patients and deaths is believed to be due to the strain on healthcare systems caused by the intensive deployment of medical personnel to COVID-19 over the past three years.

In particular, South Korea ranks first in tuberculosis prevalence and third in mortality among the 38 member countries of the Organisation for Economic Co-operation and Development (OECD). The high ranking of tuberculosis prevalence in South Korea is largely attributed to the impact of 'latent tuberculosis,' which is not outwardly visible. Latent tuberculosis refers to a state where a person is infected with the tuberculosis bacteria but does not develop symptoms because the disease has not actually manifested. While latent tuberculosis does not transmit the disease to others, it can develop into active tuberculosis and spread to those nearby if the immune system weakens, making early diagnosis and prevention through screening crucial.

Tuberculosis is a chronic respiratory infectious disease transmitted through the air by the tuberculosis bacteria. When a tuberculosis patient coughs or sneezes, infectious particles containing the bacteria are released into the air and can be inhaled by others, leading to infection in the lungs. However, infection does not always lead to active tuberculosis. About 30% of contacts become infected, and only about 10% of those infected develop active tuberculosis. The remaining 90% live as latent tuberculosis carriers without any symptoms.

Latent tuberculosis usually causes no noticeable issues, but tuberculosis can develop when immunity decreases during seasonal changes. Among latent tuberculosis patients, 10% develop active tuberculosis. Of these, 50% develop the disease within 1 to 2 years, while the other half typically develop it when their immunity declines during daily life. According to 2021 domestic tuberculosis patient statistics, those aged 70 to 80 account for about half, 42.7% (9,777 people), of all tuberculosis patients. This is likely because older patients have a higher risk of tuberculosis due to weakened immunity. The incidence also increases in people with underlying conditions such as diabetes, so if immunity frequently decreases or there has been a tuberculosis patient nearby, it is advisable to detect latent tuberculosis through testing and treat it early.

[Photo by GC Green Cross Medical Foundation]

Latent tuberculosis is difficult to detect with common tuberculosis tests such as chest X-rays and sputum tests. A separate test that uses the immunological response to tuberculosis antigens present in the body is required. The 'tuberculin skin test' and 'interferon-gamma release assay (IGRA)' are mainly used.

The tuberculin skin test has been widely used for a long time. However, the procedure is cumbersome, and especially in South Korea, the BCG vaccination for tuberculosis or infection with non-tuberculous mycobacteria can cause false negatives or false positives. There is also a risk of adverse reactions due to the test being performed inside the body.

On the other hand, IGRA can diagnose latent tuberculosis with a single blood draw, offering high convenience, and since it is an in vitro test, the risk of adverse reactions from drug injection is low. It uses specific antigens that stimulate only T cells sensitized to tuberculosis bacteria and measures the concentration of interferon-gamma by enzyme-linked immunosorbent assay (ELISA) to determine infection status. It is less affected by the BCG vaccine, resulting in higher accuracy. In the United States, Europe, and other regions, IGRA, which can detect latent tuberculosis with a single blood draw, is primarily recommended, and in South Korea, the coverage criteria for IGRA are also expanding.

Dr. Lee Gyu-taek, a specialist in diagnostic laboratory medicine at GC Green Cross Medical Foundation, said, “As the risk of tuberculosis has increased due to the imbalance in the healthcare system caused by COVID-19, if you belong to a high-risk group for tuberculosis, we recommend proactively preventing it by confirming tuberculosis infection status through IGRA.”