by Dr. Paul Han
Tuberculosis is still the world’s deadliest infection, causing disease in nearly 10 million people, and leading to 1.6 million deaths each year. Tb has been one of the most common causes of death throughout human history. In Korea, TB was a major problem after the Korean War, with active disease affecting one out of every twenty people. Korea currently has the highest rate of TB among developed countries.
For most patients, TB causes a lung infection, that can cause permanent damage to the lungs, or lead to death. Occasional, TB can cause an infection in other parts of the body, like the brain, bones, intestines, or bladder. In many cases, TB can be difficult to treat, because it can easily become resistant to medications. Part of the reason that TB is so dangerous is that it is highly contagious; the bacteria can be transmitted through the air when a patient coughs. Active TB usually spreads from person-to-person– most often affecting family members, close friends or co-workers. Especially for caretakers of children, the spread of TB can be disastrous.
Fortunately, most cases of TB can be prevented by early detection and prophylactic treatment of Latent TB Infection (LTBI).
LATENT TB INFECTION
When patients come in contact with TB, many people do not get sick right away, but rather they become carriers. The TB bacteria can stay in the body in a quiet phase, sometimes for many decades, unbeknownst to the patient. This phase of TB is called Latent TB Infection. When patients have Latent TB, they are usually not sick, and they are not contagious. Eventually (in approximately twenty percent of patients), the bacteria can become active again, as patients age and develop comorbidities.
Treatment during the latent phase of infection can eliminate the bacteria before it becomes active. Two treatment regimens now are commonly used to treat Latent TB Infection: Rifampin for four months, or Isoniazid for six to nine months. These medications are generally safe, though patients should be counselled regarding potential side effects, such as liver toxicity. The risk of having an adverse reaction from these medications is far less than the risk of developing tuberculosis.
TESTING FOR LATENT TB
According to government estimates, about 1 in 3 Koreans actually have latent TB. Testing for latent TB Infection consists of blood tests, called interferon gamma release assays (IGRAs). In the United States, two different IGRAs are commonly performed: the Quantiferon TB gold, and the T-spot Test. These tests differ from the older skin tests (PPD), because they will not react in patients who have had the BCG vaccine*.
A positive IGRA indicates that the patient has had some definite infection with TB. The IGRA could be positive due to latent TB, active infection or previous treatment. A CXR or sputum test is usually performed to make sure that there is no evidence of active disease, because treatment for active TB requires different medications (and taking a prophylactic treatment during active disease can actually lead to resistance). In some cases, the IGRA is positive due to previously treated TB, which does not require any further treatment. If the patient has no ongoing infection or previous treatment, the positive IGRA is due to Latent TB Infection and prophylactic treatment should be taken. Of note, the IGRA will always remain positive even after treatment.
Most patients who immigrate to the United States undergo testing for TB. TB testing is also performed in close contacts of active TB cases. When patients are identified with TB, the Department of Health will make recommendations for treatment and provide anti-tuberculosis medications for anyone who is infected. These policies have been effective at almost eliminating TB from people born in the United States. Korea is currently also undergoing policy changes to screen high-risk groups and provide treatments similar to the US policy.
Despite the deadly effects of TB, we do have hope that TB can someday be eliminated from both Koreans and Korean-Americans, but this will require a group effort. Treatment can help individuals who develop TB, but screening and prophylaxis are the keys to stopping this disease from spreading in the community.
*Of note, the BCG vaccine is usually given to Korean children. BCG has been shown to be partially effective, but the protective effects last approximately 10 to 15 years. The United States does not routinely administer BCG vaccine to children.
Paul Han, MD, FCCP
Pulmonary Specialists of North Jersey
Sethuraman, Nandini; Jeremiah, Sundararaj Stanleyraj.
Interpreting Diagnostic Tests for SARS-CoV-2. JAMA:
May 6, 2020.