Tuberculosis (TB) is a contagious infection caused by the bacterium Mycobacterium tuberculosis that primarily affects the lungs. While TB rates have declined in many areas, the infection remains a significant public health concern worldwide. For job seekers, particularly those entering environments with close human contact, pre-employment screening for TB is a standard, and often required, part of the hiring process. Understanding this screening process can help demystify the requirement for those beginning a new job.
Why Certain Jobs Require TB Screening
TB screening is a public health strategy driven by how the disease is transmitted. Tuberculosis bacteria are spread through the air when an infected person coughs, sneezes, or speaks, releasing microscopic droplets. In settings where people are in close proximity for extended periods, the risk of transmission increases.
Jobs in specific sectors routinely mandate this testing to prevent the spread of infection to others. High-risk environments include healthcare facilities, schools, childcare centers, and assisted living facilities, where employees interact with vulnerable populations like the elderly, children, or those with compromised immune systems. Public health policy dictates that individuals who have active, transmissible TB disease should not work in these settings. Screening helps ensure a safe environment for both the workforce and the people they serve.
The Different Methods of TB Testing
Two main types of tests are used for employment screening to determine if a person has been infected with Mycobacterium tuberculosis: the Tuberculin Skin Test (TST) and the Interferon-Gamma Release Assay (IGRA). Both tests measure the body’s immune response to the TB bacteria, but they do so through different mechanisms.
The Tuberculin Skin Test, also known as the Mantoux test or PPD test, involves injecting a small amount of purified protein derivative (PPD) just beneath the skin of the forearm. This solution contains proteins derived from the TB bacteria, which will trigger a reaction if the person has been previously infected. A key disadvantage of the TST is that a prior vaccination with the Bacille Calmette-Guérin (BCG) vaccine can cause a false-positive result.
The Interferon-Gamma Release Assay (IGRA) is a blood test that detects the cellular immune response to specific TB antigens. Commercial versions, such as QuantiFERON-TB Gold, require a single blood draw. The blood sample is mixed with TB antigens in a lab to see if immune cells release interferon-gamma (IFN-γ).
The IGRA is often preferred for those who have received the BCG vaccine because its results are not affected by the vaccination, making it more specific for Mycobacterium tuberculosis infection. While IGRAs are generally more expensive, they only require one visit, unlike the TST.
The Testing Procedure and Result Interpretation
The procedure for testing differs based on the method chosen for the screening. The Tuberculin Skin Test requires two separate visits to a healthcare provider. During the first visit, a small amount of PPD solution is injected into the top layer of the skin, creating a small bump or “wheal.” The test site must then be read by a healthcare professional 48 to 72 hours later. The clinician measures the diameter of any firm, raised swelling, called induration, not the redness, to determine the result.
Conversely, the IGRA procedure only requires a standard blood draw. The collected blood sample is sent to a laboratory for analysis, and results are typically available much sooner than the TST, often within 24 to 48 hours. A negative result from either test generally indicates that the person has not been infected with the TB bacteria.
A positive result from either the TST or the IGRA indicates that the individual has been exposed to the bacteria at some point. A positive screening result does not distinguish between Latent TB Infection (LTBI) and Active TB Disease. Latent TB means the bacteria are present in the body but are inactive, causing no symptoms and making the person non-contagious. Active TB means the bacteria are multiplying, causing illness, and the person can transmit the infection to others.
What Happens After a Positive TB Test
A positive initial screening test necessitates further evaluation to determine the status of the infection. The most common next step is a chest X-ray, which helps to identify any signs of active TB disease in the lungs.
If the chest X-ray is abnormal or if the person is experiencing symptoms like a persistent cough, unexplained weight loss, or night sweats, a sputum test may also be required. Sputum is the thick mucus coughed up from the lungs, and laboratory analysis of this sample can confirm the presence of active, contagious bacteria.
If the evaluation determines the person has Latent TB Infection (LTBI), they are generally not considered a transmission risk and can safely begin or continue working. Treatment for LTBI is usually recommended to prevent the inactive infection from progressing into active disease later.
Individuals with LTBI often receive medical clearance for employment, sometimes requiring periodic symptom screenings. If Active TB Disease is confirmed, the individual is contagious and will be temporarily excluded from the workplace. They must complete a course of treatment and be deemed non-infectious by public health authorities. They can return to work once they receive medical clearance, which typically happens after a few weeks of effective treatment.