Tuberculosis: Still a Modern Threat

Tuberculosis

For many people who live in developed countries, thoughts of Tuberculosis  harken back to the Industrial Revolution, with images of weary workers coughing into bloody rags, and eventually landing in sanatoriums to languish and often to die.  It was then, in the 19th century, that TB killed one out of seven people in the United States and Europe, according to the CDC. Compare those statistics to 2013, when there were only  9,582 new TB cases reported in the United States. It is fair to say that TB is still an infectious disease threat, but no longer preoccupies the minds of U.S. citizens.

Despite this shift in public consciousness about TB, there are statistics that indicate that TB is still very much an issue worth addressing in today’s society. For example, the Center for Disease Control and Prevention (CDC) reports that in 2013, 9 million people worldwide were infected with TB, and 1.5 million people died as a result of the infection. Tuberculosis is the second leading cause of death from all infectious diseases, lagging only behind HIV/AIDS.  Dr. Fred Kohanna, AllOne Health’s Corporate Medical Director, notes that “We must remain vigilant with regard to TB. The recent development of highly antibiotic resistant strains of TB is an immediate threat to public health, which makes the aggressive antibiotic treatment of active cases essential”.

It is important to understand that there is a difference between “active” TB and “latent” TB.

Latent TB

When someone is exposed to TB, the bacteria can enter the body but not actually cause illness. The body’s immune system is able to hold the bacteria at bay and prevent active infection. This is referred to as “Latent TB Infection” (LTBI). 90% of exposed individuals will never develop active TB infection. The exposed individual could develop a positive TB skin test within 2-10 weeks of the exposure. The risk of developing active TB infection is greatest in the first 2 years after the exposure. LTBI can reactivate and cause infection in 5-10% of people over the course of their lifetime. For this reason, people with LTBI are offered prophylactic antibiotics for up to 9 months to prevent reactivation of TB in the future. Treatment of latent TB infection is essential to controlling TB, because it substantially reduces the risk that TB infection will progress to active TB disease.  Treatment for LTBI is not required by public health authorities, but it is recommended.  Employees with LTBI (positive TB test but no symptoms and a negative chest x-ray) can continue to work and are not contagious.

Active TB Disease

For some individuals who are exposed to TB, the bacteria will begin to multiply and will cause an illness characterized by productive cough, fever, chills, fatigue, chest discomfort, night sweats, and weight loss. This is active TB and it is highly contagious. Active TB is reportable to public health authorities and requires isolation and mandatory antibiotic treatment.  Public health officials will typically provide advice regarding follow-up testing and monitoring for potentially exposed individuals both at work and outside of work.  An employee with active TB must not be at work until determined they are no longer infectious by public health authorities.

You might be surprised to know that 1/3 of the world’s population is infected with TB. The majority of these individuals have latent TB and not active TB. The most common way to test for TB is by means of a skin test. An extract of TB, Tuberculin, is injected into the skin and then the size of the resulting “bump” (known as induration) is measured after incubation for 48 to 72 hours. Induration greater than a predetermined diameter is considered “positive”. This test will not differentiate latent from active TB.

There are a number of ways that a TB skin test can result in a false positive. A false positive can occur as a result of the subjectivity of measuring the amount of induration, itching at the injection site, unrelated irritation, and perhaps surprisingly, as a result of previously receiving the BCG vaccine. The BCG vaccine is generally only administered in areas where individuals are at an increased risk of being infected with TB, and in those areas it is generally administered to children. In the United States individuals most likely to receive the BCG vaccine are those who frequently travel to foreign countries where TB infection is more common. The reported efficacy of the vaccine varies, however, the most commonly reported effectiveness rates are between 60 and 80 percent and are thought to vary by geographic location. It is common for those who have received the BCG vaccine to test positive on a TB skin test, although it cannot be determined if the result is due to the BCG vaccine, or because the individual has actually been exposed to TB. The best way to ensure an accurate result is to perform a blood test (e.g. Quantiferon Gold or T-Spot) on those who have a positive TB skin test. A blood test will provide accurate information regarding previous exposure to TB, and will not be affected by prior BCG vaccination.

For companies that employ individuals at high risk to become exposed and  / or infected with the disease, screening for active and latent TB is good medical practice and may be a regulatory requirement.  Examples of employees who might require TB monitoring are those who perform work in healthcare facilities, work and live in close quarters such as housing “camps” and off-shore oil rigs, and those who travel internationally to TB endemic countries.  Testing should be performed at the start of employment in a high risk environment and should be repeated annually as long as the risk remains, or more frequently if there has been a known exposure.  The newer testing methodologies have simplified the process by eliminating the need to return for medical assessment 2 – 3 days after the test was performed, like in a TB skin test.  With the newer blood tests, TB evaluation can be done in one visit. This one step test is a major advanced in simplifying the testing process and improving test accuracy.  The employer should be aware of the possible risk of TB exposure to their employees if their employees live or work in the situations mentioned above.  Testing is a simple way to protect your population. 

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