[Contribution] Managing latent TB infection is key to eliminating TB

Tuberculosis (TB) is an infectious disease that has plagued humanity for a long time. It is still one of the leading causes of death worldwide, with around 10 million new cases annually. What is the current status of TB in Korea, then?

Since the Korean War (1950-53), the number of TB cases in Korea has increased dramatically. However, through active TB control programs and overseas support, the number of TB cases and deaths has sharply dropped. I think it is an achievement comparable to Korea’s economic growth.

There was a period of stagnation in TB control. However, between 2011 and 2022, when the pandemic was at its peak, the number of TB patients steadily declined. The recent achievements in TB control are attributable to the strong management of latent TB infection.

Despite the increased focus on latent TB infection, it is a relatively new concept and is often confused with regular TB.

To understand latent TB infection, it is important to understand how TB is transmitted and how it develops. It is an airborne disease spread by inhaling TB bacteria exhaled by a person with respiratory TB, but not everyone who is infected with TB bacteria will develop TB. Only 5-10 percent of infected people develop TB. In most cases, the body’s immune system suppresses the growth of TB bacteria, and the disease remains undiagnosed, a condition known as latent tuberculosis infection (LTBI).

LTBI has no symptoms and does not show up on sputum tests or chest X-rays, so it was not subject to diagnosis and treatment in the past.

However, with the decline of tuberculosis, it has long been practiced in most developed countries to manage infected people who are potential TB patients to prevent the development and spread of the disease. In addition, breakthrough tests have been introduced to diagnose people with TB, increasing the accuracy of diagnosis. The previously used skin test requires the direct injection of TB antigens into the person, causing side effects and difficulty in judgment because there are many false positives caused by BCG vaccination.

The interferon-gamma release assay (IGRA) has been developed to improve upon the problems with skin prick tests. IGRA, which uses TB-specific antigens to diagnose people who are negative as negative, has a high specificity and is more objective than the skin test.

However, the IGRA can only determine whether a person is infected with tuberculosis, not the likelihood of developing the disease. Also, since the test uses the immune response, the results are not 100 percent accurate. If the infection is confirmed, people must take anti-TB drugs for several months for preventive treatment.

Therefore, testing for latent TB infection is recommended for people at high risk of contracting or developing TB. People who have recently had contact with a TB patient, healthcare workers who are likely to come into contact with TB patients, and transplant patients are the main targets for screening for latent TB infection.

In Korea, school TB outbreaks became a major social issue in the 2000s. The outbreak of TB among adolescents, which was thought to be an extinct disease, was a major shock. That has led to the strengthening of TB contact investigation and the introducing of a policy to diagnose and treat latent TB infection in addition to the existing chest X-ray test.

The government supports testing and treatment for TB contacts within families and congregate settings. Recent TB reports show a significant decrease in cases in the 15-19-year-old age group, thanks to the government’s active contact investigation and preventive treatment of infected individuals.

The incidence of TB is known to be higher among healthcare workers than the general population. In particular, they are more likely to be infected in departments that treat TB patients. The impact of a TB outbreak among healthcare workers can be devastating, as it can spread to immunocompromised or weak patients in the hospital, leading to severe TB. There have been cases of newborns developing tuberculous meningitis due to a TB-positive nursery worker. As a result, screening for TB and latent TB infection has been strengthened for medical staff.

Korea has set a lofty goal of eliminating tuberculosis (TB). To achieve that goal, it must take many measures. As no breakthrough technology has yet been developed to prevent TB, the importance of managing latent TB infection is even higher. Suppose Korea continues to build on its progress and expand screening and preventive treatment for latent TB infection. In that case, it can achieve the elimination of TB it has aspired for the past several decades.